Nix is a purely functional package manager. This means that it treats packages like values in purely functional programming languages such as Haskell — they are built by functions that don’t have side-effects, and they never change after they have been built. Nix stores packages in the Nix store, usually the directory /nix/store, where each package has its own unique subdirectory such as
/nix/store/b6gvzjyb2pg0kjfwrjmg1vfhh54ad73z-firefox-33.1/
where b6gvzjyb2pg0… is a unique identifier for the package that captures all its dependencies (it’s a cryptographic hash of the package’s build dependency graph). This enables many powerful features.
You can have multiple versions or variants of a package installed at the same time. This is especially important when different applications have dependencies on different versions of the same package — it prevents the “DLL hell”. Because of the hashing scheme, different versions of a package end up in different paths in the Nix store, so they don’t interfere with each other.
An important consequence is that operations like upgrading or uninstalling an application cannot break other applications, since these operations never “destructively” update or delete files that are used by other packages.
Nix helps you make sure that package dependency specifications are complete. In general, when you’re making a package for a package management system like RPM, you have to specify for each package what its dependencies are, but there are no guarantees that this specification is complete. If you forget a dependency, then the package will build and work correctly on your machine if you have the dependency installed, but not on the end user's machine if it's not there.
Since Nix on the other hand doesn’t install packages in “global” locations like /usr/bin but in package-specific directories, the risk of incomplete dependencies is greatly reduced. This is because tools such as compilers don’t search in per-packages directories such as /nix/store/5lbfaxb722zp…-openssl-0.9.8d/include, so if a package builds correctly on your system, this is because you specified the dependency explicitly. This takes care of the build-time dependencies.
Once a package is built, runtime dependencies are found by scanning binaries for the hash parts of Nix store paths (such as r8vvq9kq…). This sounds risky, but it works extremely well.
Nix has multi-user support. This means that non-privileged users can securely install software. Each user can have a different profile, a set of packages in the Nix store that appear in the user’s PATH. If a user installs a package that another user has already installed previously, the package won’t be built or downloaded a second time. At the same time, it is not possible for one user to inject a Trojan horse into a package that might be used by another user.
Since package management operations never overwrite packages in the Nix store but just add new versions in different paths, they are atomic. So during a package upgrade, there is no time window in which the package has some files from the old version and some files from the new version — which would be bad because a program might well crash if it’s started during that period.
And since packages aren’t overwritten, the old versions are still there after an upgrade. This means that you can roll back to the old version:
Nix $ nix-env --upgrade some-packages
$ nix-env --rollback
When you uninstall a package like this…
$ nix-env --uninstall firefox
the package isn’t deleted from the system right away (after all, you might want to do a rollback, or it might be in the profiles of other users). Instead, unused packages can be deleted safely by running the garbage collector:
$ nix-collect-garbage
This deletes all packages that aren’t in use by any user profile or by a currently running program.
Packages are built from Nix expressions, which is a simple functional language. A Nix expression describes everything that goes into a package build action (a “derivation”): other packages, sources, the build script, environment variables for the build script, etc. Nix tries very hard to ensure that Nix expressions are deterministic: building a Nix expression twice should yield the same result.
Because it’s a functional language, it’s easy to support building variants of a package: turn the Nix expression into a function and call it any number of times with the appropriate arguments. Due to the hashing scheme, variants don’t conflict with each other in the Nix store.
Nix expressions generally describe how to build a package from source, so an installation action like
$ nix-env --install firefox
could cause quite a bit of build activity, as not only Firefox but also all its dependencies (all the way up to the C library and the compiler) would have to built, at least if they are not already in the Nix store. This is a source deployment model. For most users, building from source is not very pleasant as it takes far too long. However, Nix can automatically skip building from source and instead use a binary cache, a web server that provides pre-built binaries. For instance, when asked to build /nix/store/b6gvzjyb2pg0…-firefox-33.1 from source, Nix would first check if the file https://cache.nixos.org/b6gvzjyb2pg0….narinfo exists, and if so, fetch the pre-built binary referenced from there; otherwise, it would fall back to building from source.
We provide a large set of Nix expressions containing hundreds of existing Unix packages, the Nix Packages collection (Nixpkgs).
Nix is extremely useful for developers as it makes it easy to automatically set up the build environment for a package. Given a Nix expression that describes the dependencies of your package, the command nix-shell will build or download those dependencies if they’re not already in your Nix store, and then start a Bash shell in which all necessary environment variables (such as compiler search paths) are set.
For example, the following command gets all dependencies of the Pan newsreader, as described by its Nix expression:
$ nix-shell '<nixpkgs>' -A pan
You’re then dropped into a shell where you can edit, build and test the package:
[nix-shell]$ tar xf $src [nix-shell]$ cd pan-* [nix-shell]$ ./configure [nix-shell]$ make [nix-shell]$ ./pan/gui/pan
NixOS is a Linux distribution based on Nix. It uses Nix not just for package management but also to manage the system configuration (e.g., to build configuration files in /etc). This means, among other things, that it is easy to roll back the entire configuration of the system to an earlier state. Also, users can install software without root privileges. For more information and downloads, see the NixOS homepage.
Nix is released under the terms of the GNU LGPLv2.1 or (at your option) any later version.
Nix uses the linenoise-ng library, which has the following license:
linenoise.cpp
=============
Copyright (c) 2010, Salvatore Sanfilippo <antirez at gmail dot com>
Copyright (c) 2010, Pieter Noordhuis <pcnoordhuis at gmail dot com>
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
* Neither the name of Redis nor the names of its contributors may be used
to endorse or promote products derived from this software without
specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
wcwidth.cpp
===========
Markus Kuhn -- 2007-05-26 (Unicode 5.0)
Permission to use, copy, modify, and distribute this software
for any purpose and without fee is hereby granted. The author
disclaims all warranties with regard to this software.
ConvertUTF.cpp
==============
Copyright 2001-2004 Unicode, Inc.
Disclaimer
This source code is provided as is by Unicode, Inc. No claims are
made as to fitness for any particular purpose. No warranties of any
kind are expressed or implied. The recipient agrees to determine
applicability of information provided. If this file has been
purchased on magnetic or optical media from Unicode, Inc., the
sole remedy for any claim will be exchange of defective media
within 90 days of receipt.
Limitations on Rights to Redistribute This Code
Unicode, Inc. hereby grants the right to freely use the information
supplied in this file in the creation of products supporting the
Unicode Standard, and to make copies of this file in any form
for internal or external distribution as long as this notice
remains attached.
This chapter is for impatient people who don't like reading documentation. For more in-depth information you are kindly referred to subsequent chapters.
Install single-user Nix by running the following:
$ bash <(curl https://nixos.org/nix/install)
This will install Nix in /nix. The install script will create /nix using sudo, so make sure you have sufficient rights. (For other installation methods, see Part II, “Installation”.)
See what installable packages are currently available in the channel:
$ nix-env -qa
docbook-xml-4.3
docbook-xml-4.5
firefox-33.0.2
hello-2.9
libxslt-1.1.28
...
Install some packages from the channel:
$ nix-env -i hello
This should download pre-built packages; it should not build them locally (if it does, something went wrong).
Test that they work:
$ which hello /home/eelco/.nix-profile/bin/hello $ hello Hello, world!
Uninstall a package:
$ nix-env -e hello
You can also test a package without installing it:
$ nix-shell -p hello
This builds or downloads GNU Hello and its dependencies, then drops you into a Bash shell where the hello command is present, all without affecting your normal environment:
[nix-shell:~]$ hello Hello, world! [nix-shell:~]$ exit $ hello hello: command not found
To keep up-to-date with the channel, do:
$ nix-channel --update nixpkgs $ nix-env -u '*'
The latter command will upgrade each installed package for which there is a “newer” version (as determined by comparing the version numbers).
If you're unhappy with the result of a nix-env action (e.g., an upgraded package turned out not to work properly), you can go back:
$ nix-env --rollback
You should periodically run the Nix garbage collector to get rid of unused packages, since uninstalls or upgrades don't actually delete them:
$ nix-collect-garbage -d
This section describes how to install and configure Nix for first-time use.
Nix is currently supported on the following platforms:
Linux (i686, x86_64, aarch64).
macOS (x86_64).
If you are using Linux or macOS, the easiest way to install Nix is to run the following command:
$ sh <(curl https://nixos.org/nix/install)
As of Nix 2.1.0, the Nix installer will always default to creating a single-user installation, however opting in to the multi-user installation is highly recommended.
To explicitly select a single-user installation on your system:
sh <(curl https://nixos.org/nix/install) --no-daemon
This will perform a single-user installation of Nix, meaning that /nix is owned by the invoking user. You should run this under your usual user account, not as root. The script will invoke sudo to create /nix if it doesn’t already exist. If you don’t have sudo, you should manually create /nix first as root, e.g.:
$ mkdir /nix $ chown alice /nix
The install script will modify the first writable file from amongst .bash_profile, .bash_login and .profile to source ~/.nix-profile/etc/profile.d/nix.sh. You can set the NIX_INSTALLER_NO_MODIFY_PROFILE environment variable before executing the install script to disable this behaviour.
You can uninstall Nix simply by running:
$ rm -rf /nix
The multi-user Nix installation creates system users, and a system service for the Nix daemon.
Supported Systems
Linux running systemd, with SELinux disabled
macOS
You can instruct the installer to perform a multi-user installation on your system:
sh <(curl https://nixos.org/nix/install) --daemon
The multi-user installation of Nix will create build users between the user IDs 30001 and 30032, and a group with the group ID 30000. You should run this under your usual user account, not as root. The script will invoke sudo as needed.
The installer will modify /etc/bashrc, and /etc/zshrc if they exist. The installer will first back up these files with a .backup-before-nix extension. The installer will also create /etc/profile.d/nix.sh.
You can uninstall Nix with the following commands:
sudo rm -rf /etc/profile/nix.sh /etc/nix /nix ~root/.nix-profile ~root/.nix-defexpr ~root/.nix-channels ~/.nix-profile ~/.nix-defexpr ~/.nix-channels # If you are on Linux with systemd, you will need to run: sudo systemctl stop nix-daemon.socket sudo systemctl stop nix-daemon.service sudo systemctl disable nix-daemon.socket sudo systemctl disable nix-daemon.service sudo systemctl daemon-reload # If you are on macOS, you will need to run: sudo launchctl unload /Library/LaunchDaemons/org.nixos.nix-daemon.plist sudo rm /Library/LaunchDaemons/org.nixos.nix-daemon.plist
There may also be references to Nix in /etc/profile, /etc/bashrc, and /etc/zshrc which you may remove.
NixOS.org hosts version-specific installation URLs for all Nix versions since 1.11.16, at https://nixos.org/releases/nix/nix-VERSION/install.
These install scripts can be used the same as the main NixOS.org installation script:
sh <(curl https://nixos.org/nix/install)
In the same directory of the install script are sha256 sums, and gpg signature files.
You can also download a binary tarball that contains Nix and all its dependencies. (This is what the install script at https://nixos.org/nix/install does automatically.) You should unpack it somewhere (e.g. in /tmp), and then run the script named install inside the binary tarball:
alice$ cd /tmp alice$ tar xfj nix-1.8-x86_64-darwin.tar.bz2 alice$ cd nix-1.8-x86_64-darwin alice$ ./install
If you need to edit the multi-user installation script to use different group ID or a different user ID range, modify the variables set in the file named install-multi-user.
If no binary package is available, you can download and compile a source distribution.
GNU Make.
Bash Shell. The ./configure script relies on bashisms, so Bash is required.
A version of GCC or Clang that supports C++14.
pkg-config to locate dependencies. If your distribution does not provide it, you can get it from http://www.freedesktop.org/wiki/Software/pkg-config.
The OpenSSL library to calculate cryptographic hashes. If your distribution does not provide it, you can get it from https://www.openssl.org.
The bzip2 compressor program and the libbz2 library. Thus you must have bzip2 installed, including development headers and libraries. If your distribution does not provide these, you can obtain bzip2 from https://web.archive.org/web/20180624184756/http://www.bzip.org/.
liblzma, which is provided by XZ Utils. If your distribution does not provide this, you can get it from https://tukaani.org/xz/.
cURL and its library. If your distribution does not provide it, you can get it from https://curl.haxx.se/.
The SQLite embedded database library, version 3.6.19 or higher. If your distribution does not provide it, please install it from http://www.sqlite.org/.
The Boehm garbage collector to reduce the evaluator’s memory consumption (optional). To enable it, install pkgconfig and the Boehm garbage collector, and pass the flag --enable-gc to configure.
The xmllint and xsltproc programs to build this manual and the man-pages. These are part of the libxml2 and libxslt packages, respectively. You also need the DocBook XSL stylesheets and optionally the DocBook 5.0 RELAX NG schemas. Note that these are only required if you modify the manual sources or when you are building from the Git repository.
Recent versions of Bison and Flex to build the parser. (This is because Nix needs GLR support in Bison and reentrancy support in Flex.) For Bison, you need version 2.6, which can be obtained from the GNU FTP server. For Flex, you need version 2.5.35, which is available on SourceForge. Slightly older versions may also work, but ancient versions like the ubiquitous 2.5.4a won't. Note that these are only required if you modify the parser or when you are building from the Git repository.
The source tarball of the most recent stable release can be downloaded from the Nix homepage. You can also grab the most recent development release.
Alternatively, the most recent sources of Nix can be obtained from its Git repository. For example, the following command will check out the latest revision into a directory called nix:
$ git clone https://github.com/NixOS/nix
Likewise, specific releases can be obtained from the tags of the repository.
After unpacking or checking out the Nix sources, issue the following commands:
$ ./configure options...
$ make
$ make installNix requires GNU Make so you may need to invoke gmake instead.
When building from the Git repository, these should be preceded by the command:
$ ./bootstrap.sh
The installation path can be specified by passing the --prefix= to configure. The default installation directory is prefix/usr/local. You can change this to any location you like. You must have write permission to the prefix path.
Nix keeps its store (the place where packages are stored) in /nix/store by default. This can be changed using --with-store-dir=.path
Nix keeps state (such as its database and log files) in /nix/var by default. This can be changed using --localstatedir=.path
Nix has two basic security models. First, it can be used in “single-user mode”, which is similar to what most other package management tools do: there is a single user (typically root) who performs all package management operations. All other users can then use the installed packages, but they cannot perform package management operations themselves.
Alternatively, you can configure Nix in “multi-user mode”. In this model, all users can perform package management operations — for instance, every user can install software without requiring root privileges. Nix ensures that this is secure. For instance, it’s not possible for one user to overwrite a package used by another user with a Trojan horse.
In single-user mode, all Nix operations that access the database in prefix/var/nix/dbprefix/storeroot. (If you install from RPM packages, that’s in fact the default ownership.) However, on single-user machines, it is often convenient to chown those directories to your normal user account so that you don’t have to su to root all the time.
To allow a Nix store to be shared safely among multiple users, it is important that users are not able to run builders that modify the Nix store or database in arbitrary ways, or that interfere with builds started by other users. If they could do so, they could install a Trojan horse in some package and compromise the accounts of other users.
To prevent this, the Nix store and database are owned by some privileged user (usually root) and builders are executed under special user accounts (usually named nixbld1, nixbld2, etc.). When a unprivileged user runs a Nix command, actions that operate on the Nix store (such as builds) are forwarded to a Nix daemon running under the owner of the Nix store/database that performs the operation.
root and a set of trusted users specified in nix.conf can specify arbitrary binary caches. So while unprivileged users may install packages from arbitrary Nix expressions, they may not get pre-built binaries.The build users are the special UIDs under which builds are performed. They should all be members of the build users group nixbld. This group should have no other members. The build users should not be members of any other group. On Linux, you can create the group and users as follows:
$ groupadd -r nixbld
$ for n in $(seq 1 10); do useradd -c "Nix build user $n" \
-d /var/empty -g nixbld -G nixbld -M -N -r -s "$(which nologin)" \
nixbld$n; done
This creates 10 build users. There can never be more concurrent builds than the number of build users, so you may want to increase this if you expect to do many builds at the same time.
The Nix daemon should be started as follows (as root):
$ nix-daemon
You’ll want to put that line somewhere in your system’s boot scripts.
To let unprivileged users use the daemon, they should set the NIX_REMOTE environment variable to daemon. So you should put a line like
export NIX_REMOTE=daemon
into the users’ login scripts.
To limit which users can perform Nix operations, you can use the permissions on the directory /nix/var/nix/daemon-socket. For instance, if you want to restrict the use of Nix to the members of a group called nix-users, do
$ chgrp nix-users /nix/var/nix/daemon-socket $ chmod ug=rwx,o= /nix/var/nix/daemon-socket
This way, users who are not in the nix-users group cannot connect to the Unix domain socket /nix/var/nix/daemon-socket/socket, so they cannot perform Nix operations.
To use Nix, some environment variables should be set. In particular, PATH should contain the directories prefix/bin~/.nix-profile/bin. The first directory contains the Nix tools themselves, while ~/.nix-profile is a symbolic link to the current user environment (an automatically generated package consisting of symlinks to installed packages). The simplest way to set the required environment variables is to include the file prefix/etc/profile.d/nix.sh~/.profile (or similar), like this:
source prefix/etc/profile.d/nix.shIf you need to specify a custom certificate bundle to account for an HTTPS-intercepting man in the middle proxy, you must specify the path to the certificate bundle in the environment variable NIX_SSL_CERT_FILE.
If you don't specify a NIX_SSL_CERT_FILE manually, Nix will install and use its own certificate bundle.
Set the environment variable and install Nix
$ export NIX_SSL_CERT_FILE=/etc/ssl/my-certificate-bundle.crt $ sh <(curl https://nixos.org/nix/install)
In the shell profile and rc files (for example, /etc/bashrc, /etc/zshrc), add the following line:
export NIX_SSL_CERT_FILE=/etc/ssl/my-certificate-bundle.crt
On macOS you must specify the environment variable for the Nix daemon service, then restart it:
$ sudo launchctl setenv NIX_SSL_CERT_FILE /etc/ssl/my-certificate-bundle.crt $ sudo launchctl kickstart -k system/org.nixos.nix-daemon
Multi-user Nix users on macOS can upgrade Nix by running: sudo -i sh -c 'nix-channel --update && nix-env -iA nixpkgs.nix && launchctl remove org.nixos.nix-daemon && launchctl load /Library/LaunchDaemons/org.nixos.nix-daemon.plist'
Single-user installations of Nix should run this: nix-channel --update; nix-env -iA nixpkgs.nix
This chapter discusses how to do package management with Nix, i.e., how to obtain, install, upgrade, and erase packages. This is the “user’s” perspective of the Nix system — people who want to create packages should consult Part IV, “Writing Nix Expressions”.
The main command for package management is nix-env. You can use it to install, upgrade, and erase packages, and to query what packages are installed or are available for installation.
In Nix, different users can have different “views” on the set of installed applications. That is, there might be lots of applications present on the system (possibly in many different versions), but users can have a specific selection of those active — where “active” just means that it appears in a directory in the user’s PATH. Such a view on the set of installed applications is called a user environment, which is just a directory tree consisting of symlinks to the files of the active applications.
Components are installed from a set of Nix expressions that tell Nix how to build those packages, including, if necessary, their dependencies. There is a collection of Nix expressions called the Nix Package collection that contains packages ranging from basic development stuff such as GCC and Glibc, to end-user applications like Mozilla Firefox. (Nix is however not tied to the Nix Package collection; you could write your own Nix expressions based on it, or completely new ones.)
You can manually download the latest version of Nixpkgs from http://nixos.org/nixpkgs/download.html. However, it’s much more convenient to use the Nixpkgs channel, since it makes it easy to stay up to date with new versions of Nixpkgs. (Channels are described in more detail in Chapter 12, Channels.) Nixpkgs is automatically added to your list of “subscribed” channels when you install Nix. If this is not the case for some reason, you can add it as follows:
$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable $ nix-channel --update
http://nixos.org/channels/nixos-14.12). A NixOS channel is identical to the Nixpkgs channel, except that it contains only Linux binaries and is updated only if a set of regression tests succeed.You can view the set of available packages in Nixpkgs:
$ nix-env -qa aterm-2.2 bash-3.0 binutils-2.15 bison-1.875d blackdown-1.4.2 bzip2-1.0.2 …
The flag -q specifies a query operation, and -a means that you want to show the “available” (i.e., installable) packages, as opposed to the installed packages. If you downloaded Nixpkgs yourself, or if you checked it out from GitHub, then you need to pass the path to your Nixpkgs tree using the -f flag:
$ nix-env -qaf /path/to/nixpkgs
where /path/to/nixpkgs is where you’ve unpacked or checked out Nixpkgs.
You can select specific packages by name:
$ nix-env -qa firefox firefox-34.0.5 firefox-with-plugins-34.0.5
and using regular expressions:
$ nix-env -qa 'firefox.*'
It is also possible to see the status of available packages, i.e., whether they are installed into the user environment and/or present in the system:
$ nix-env -qas … -PS bash-3.0 --S binutils-2.15 IPS bison-1.875d …
The first character (I) indicates whether the package is installed in your current user environment. The second (P) indicates whether it is present on your system (in which case installing it into your user environment would be a very quick operation). The last one (S) indicates whether there is a so-called substitute for the package, which is Nix’s mechanism for doing binary deployment. It just means that Nix knows that it can fetch a pre-built package from somewhere (typically a network server) instead of building it locally.
You can install a package using nix-env -i. For instance,
$ nix-env -i subversion
will install the package called subversion (which is, of course, the Subversion version management system).
https://cache.nixos.org; it contains binaries for most packages in Nixpkgs. Only if no binary is available in the binary cache, Nix will build the package from source. So if nix-env -i subversion results in Nix building stuff from source, then either the package is not built for your platform by the Nixpkgs build servers, or your version of Nixpkgs is too old or too new. For instance, if you have a very recent checkout of Nixpkgs, then the Nixpkgs build servers may not have had a chance to build everything and upload the resulting binaries to https://cache.nixos.org. The Nixpkgs channel is only updated after all binaries have been uploaded to the cache, so if you stick to the Nixpkgs channel (rather than using a Git checkout of the Nixpkgs tree), you will get binaries for most packages.Naturally, packages can also be uninstalled:
$ nix-env -e subversion
Upgrading to a new version is just as easy. If you have a new release of Nix Packages, you can do:
$ nix-env -u subversion
This will only upgrade Subversion if there is a “newer” version in the new set of Nix expressions, as defined by some pretty arbitrary rules regarding ordering of version numbers (which generally do what you’d expect of them). To just unconditionally replace Subversion with whatever version is in the Nix expressions, use -i instead of -u; -i will remove whatever version is already installed.
You can also upgrade all packages for which there are newer versions:
$ nix-env -u
Sometimes it’s useful to be able to ask what nix-env would do, without actually doing it. For instance, to find out what packages would be upgraded by nix-env -u, you can do
$ nix-env -u --dry-run (dry run; not doing anything) upgrading `libxslt-1.1.0' to `libxslt-1.1.10' upgrading `graphviz-1.10' to `graphviz-1.12' upgrading `coreutils-5.0' to `coreutils-5.2.1'
Profiles and user environments are Nix’s mechanism for implementing the ability to allow different users to have different configurations, and to do atomic upgrades and rollbacks. To understand how they work, it’s useful to know a bit about how Nix works. In Nix, packages are stored in unique locations in the Nix store (typically, /nix/store). For instance, a particular version of the Subversion package might be stored in a directory /nix/store/dpmvp969yhdqs7lm2r1a3gng7pyq6vy4-subversion-1.1.3/, while another version might be stored in /nix/store/5mq2jcn36ldlmh93yj1n8s9c95pj7c5s-subversion-1.1.2. The long strings prefixed to the directory names are cryptographic hashes[1] of all inputs involved in building the package — sources, dependencies, compiler flags, and so on. So if two packages differ in any way, they end up in different locations in the file system, so they don’t interfere with each other. Figure 10.1, “User environments” shows a part of a typical Nix store.
Of course, you wouldn’t want to type
$ /nix/store/dpmvp969yhdq...-subversion-1.1.3/bin/svn
every time you want to run Subversion. Of course we could set up the PATH environment variable to include the bin directory of every package we want to use, but this is not very convenient since changing PATH doesn’t take effect for already existing processes. The solution Nix uses is to create directory trees of symlinks to activated packages. These are called user environments and they are packages themselves (though automatically generated by nix-env), so they too reside in the Nix store. For instance, in Figure 10.1, “User environments” the user environment /nix/store/0c1p5z4kda11...-user-env contains a symlink to just Subversion 1.1.2 (arrows in the figure indicate symlinks). This would be what we would obtain if we had done
$ nix-env -i subversion
on a set of Nix expressions that contained Subversion 1.1.2.
This doesn’t in itself solve the problem, of course; you wouldn’t want to type /nix/store/0c1p5z4kda11...-user-env/bin/svn either. That’s why there are symlinks outside of the store that point to the user environments in the store; for instance, the symlinks default-42-link and default-43-link in the example. These are called generations since every time you perform a nix-env operation, a new user environment is generated based on the current one. For instance, generation 43 was created from generation 42 when we did
$ nix-env -i subversion firefox
on a set of Nix expressions that contained Firefox and a new version of Subversion.
Generations are grouped together into profiles so that different users don’t interfere with each other if they don’t want to. For example:
$ ls -l /nix/var/nix/profiles/ ... lrwxrwxrwx 1 eelco ... default-42-link -> /nix/store/0c1p5z4kda11...-user-env lrwxrwxrwx 1 eelco ... default-43-link -> /nix/store/3aw2pdyx2jfc...-user-env lrwxrwxrwx 1 eelco ... default -> default-43-link
This shows a profile called default. The file default itself is actually a symlink that points to the current generation. When we do a nix-env operation, a new user environment and generation link are created based on the current one, and finally the default symlink is made to point at the new generation. This last step is atomic on Unix, which explains how we can do atomic upgrades. (Note that the building/installing of new packages doesn’t interfere in any way with old packages, since they are stored in different locations in the Nix store.)
If you find that you want to undo a nix-env operation, you can just do
$ nix-env --rollback
which will just make the current generation link point at the previous link. E.g., default would be made to point at default-42-link. You can also switch to a specific generation:
$ nix-env --switch-generation 43
which in this example would roll forward to generation 43 again. You can also see all available generations:
$ nix-env --list-generations
You generally wouldn’t have /nix/var/nix/profiles/ in your some-profile/binPATH. Rather, there is a symlink ~/.nix-profile that points to your current profile. This means that you should put ~/.nix-profile/bin in your PATH (and indeed, that’s what the initialisation script /nix/etc/profile.d/nix.sh does). This makes it easier to switch to a different profile. You can do that using the command nix-env --switch-profile:
$ nix-env --switch-profile /nix/var/nix/profiles/my-profile $ nix-env --switch-profile /nix/var/nix/profiles/default
These commands switch to the my-profile and default profile, respectively. If the profile doesn’t exist, it will be created automatically. You should be careful about storing a profile in another location than the profiles directory, since otherwise it might not be used as a root of the garbage collector (see Chapter 11, Garbage Collection).
All nix-env operations work on the profile pointed to by ~/.nix-profile, but you can override this using the --profile option (abbreviation -p):
$ nix-env -p /nix/var/nix/profiles/other-profile -i subversion
This will not change the ~/.nix-profile symlink.
nix-env operations such as upgrades (-u) and uninstall (-e) never actually delete packages from the system. All they do (as shown above) is to create a new user environment that no longer contains symlinks to the “deleted” packages.
Of course, since disk space is not infinite, unused packages should be removed at some point. You can do this by running the Nix garbage collector. It will remove from the Nix store any package not used (directly or indirectly) by any generation of any profile.
Note however that as long as old generations reference a package, it will not be deleted. After all, we wouldn’t be able to do a rollback otherwise. So in order for garbage collection to be effective, you should also delete (some) old generations. Of course, this should only be done if you are certain that you will not need to roll back.
To delete all old (non-current) generations of your current profile:
$ nix-env --delete-generations old
Instead of old you can also specify a list of generations, e.g.,
$ nix-env --delete-generations 10 11 14
To delete all generations older than a specified number of days (except the current generation), use the d suffix. For example,
$ nix-env --delete-generations 14d
deletes all generations older than two weeks.
After removing appropriate old generations you can run the garbage collector as follows:
$ nix-store --gc
The behaviour of the gargage collector is affected by the keep- derivations (default: true) and keep-outputs (default: false) options in the Nix configuration file. The defaults will ensure that all derivations that are not build-time dependencies of garbage collector roots will be collected but that all output paths that are not runtime dependencies will be collected. (This is usually what you want, but while you are developing it may make sense to keep outputs to ensure that rebuild times are quick.) If you are feeling uncertain, you can also first view what files would be deleted:
$ nix-store --gc --print-dead
Likewise, the option --print-live will show the paths that won’t be deleted.
There is also a convenient little utility nix-collect-garbage, which when invoked with the -d (--delete-old) switch deletes all old generations of all profiles in /nix/var/nix/profiles. So
$ nix-collect-garbage -d
is a quick and easy way to clean up your system.
The roots of the garbage collector are all store paths to which there are symlinks in the directory prefix/nix/var/nix/gcroots/nix/store/d718ef...-foo a root of the collector:
$ ln -s /nix/store/d718ef...-foo /nix/var/nix/gcroots/bar
That is, after this command, the garbage collector will not remove /nix/store/d718ef...-foo or any of its dependencies.
Subdirectories of prefix/nix/var/nix/gcroots
If you want to stay up to date with a set of packages, it’s not very convenient to manually download the latest set of Nix expressions for those packages and upgrade using nix-env. Fortunately, there’s a better way: Nix channels.
A Nix channel is just a URL that points to a place that contains a set of Nix expressions and a manifest. Using the command nix-channel you can automatically stay up to date with whatever is available at that URL.
You can “subscribe” to a channel using nix-channel --add, e.g.,
$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
subscribes you to a channel that always contains that latest version of the Nix Packages collection. (Subscribing really just means that the URL is added to the file ~/.nix-channels, where it is read by subsequent calls to nix-channel --update.) You can “unsubscribe” using nix-channel --remove:
$ nix-channel --remove nixpkgs
To obtain the latest Nix expressions available in a channel, do
$ nix-channel --update
This downloads and unpacks the Nix expressions in every channel (downloaded from url/nixexprs.tar.bz2~/.nix-defexpr/channels). Consequently, you can then say
$ nix-env -u
to upgrade all packages in your profile to the latest versions available in the subscribed channels.
Sometimes you want to copy a package from one machine to another. Or, you want to install some packages and you know that another machine already has some or all of those packages or their dependencies. In that case there are mechanisms to quickly copy packages between machines.
You can easily share the Nix store of a machine via HTTP. This allows other machines to fetch store paths from that machine to speed up installations. It uses the same binary cache mechanism that Nix usually uses to fetch pre-built binaries from https://cache.nixos.org.
The daemon that handles binary cache requests via HTTP, nix-serve, is not part of the Nix distribution, but you can install it from Nixpkgs:
$ nix-env -i nix-serve
You can then start the server, listening for HTTP connections on whatever port you like:
$ nix-serve -p 8080
To check whether it works, try the following on the client:
$ curl http://avalon:8080/nix-cache-info
which should print something like:
StoreDir: /nix/store WantMassQuery: 1 Priority: 30
On the client side, you can tell Nix to use your binary cache using --option extra-binary-caches, e.g.:
$ nix-env -i firefox --option extra-binary-caches http://avalon:8080/
The option extra-binary-caches tells Nix to use this binary cache in addition to your default caches, such as https://cache.nixos.org. Thus, for any path in the closure of Firefox, Nix will first check if the path is available on the server avalon or another binary caches. If not, it will fall back to building from source.
You can also tell Nix to always use your binary cache by adding a line to the nix.conf configuration file like this:
binary-caches = http://avalon:8080/ https://cache.nixos.org/
The command nix-copy-closure copies a Nix store path along with all its dependencies to or from another machine via the SSH protocol. It doesn’t copy store paths that are already present on the target machine. For example, the following command copies Firefox with all its dependencies:
$ nix-copy-closure --to alice@itchy.example.org $(type -p firefox)
See nix-copy-closure(1) for details.
With nix-store --export and nix-store --import you can write the closure of a store path (that is, the path and all its dependencies) to a file, and then unpack that file into another Nix store. For example,
$ nix-store --export $(nix-store -qR $(type -p firefox)) > firefox.closure
writes the closure of Firefox to a file. You can then copy this file to another machine and install the closure:
$ nix-store --import < firefox.closure
Any store paths in the closure that are already present in the target store are ignored. It is also possible to pipe the export into another command, e.g. to copy and install a closure directly to/on another machine:
$ nix-store --export $(nix-store -qR $(type -p firefox)) | bzip2 | \
ssh alice@itchy.example.org "bunzip2 | nix-store --import"However, nix-copy-closure is generally more efficient because it only copies paths that are not already present in the target Nix store.
You can tell Nix to automatically fetch needed binaries from a remote Nix store via SSH. For example, the following installs Firefox, automatically fetching any store paths in Firefox’s closure if they are available on the server avalon:
$ nix-env -i firefox --substituters ssh://alice@avalon
This works similar to the binary cache substituter that Nix usually uses, only using SSH instead of HTTP: if a store path P is needed, Nix will first check if it’s available in the Nix store on avalon. If not, it will fall back to using the binary cache substituter, and then to building from source.
You can also copy the closure of some store path, without installing it into your profile, e.g.
$ nix-store -r /nix/store/m85bxg…-firefox-34.0.5 --substituters ssh://alice@avalon
This is essentially equivalent to doing
$ nix-copy-closure --from alice@avalon /nix/store/m85bxg…-firefox-34.0.5
You can use SSH’s forced command feature to set up a restricted user account for SSH substituter access, allowing read-only access to the local Nix store, but nothing more. For example, add the following lines to sshd_config to restrict the user nix-ssh:
Match User nix-ssh AllowAgentForwarding no AllowTcpForwarding no PermitTTY no PermitTunnel no X11Forwarding no ForceCommand nix-store --serve Match All
On NixOS, you can accomplish the same by adding the following to your configuration.nix:
nix.sshServe.enable = true; nix.sshServe.keys = [ "ssh-dss AAAAB3NzaC1k... bob@example.org" ];
where the latter line lists the public keys of users that are allowed to connect.
Nix has built-in support for storing and fetching store paths from Amazon S3 and S3 compatible services. This uses the same binary cache mechanism that Nix usually uses to fetch prebuilt binaries from cache.nixos.org.
The following options can be specified as URL parameters to the S3 URL:
profile The name of the AWS configuration profile to use. By default Nix will use the default profile.
region The region of the S3 bucket. us–east-1 by default.
If your bucket is not in us–east-1, you should always explicitly specify the region parameter.
endpointThe URL to your S3-compatible service, for when not using Amazon S3. Do not specify this value if you're using Amazon S3.
In this example we will use the bucket named example-nix-cache.
If your binary cache is publicly accessible and does not require authentication, the simplest and easiest way to use Nix with your S3 compatible binary cache is to use the HTTP URL for that cache.
For AWS S3 the binary cache URL for example bucket will be exactly https://example-nix-cache.s3.amazonaws.com or s3://example-nix-cache. For S3 compatible binary caches, consult that cache's documentation.
Your bucket will need the following bucket policy:
{
"Id": "DirectReads",
"Version": "2012-10-17",
"Statement": [
{
"Sid": "AlowDirectReads",
"Action": [
"s3:GetObject",
"s3:GetBucketLocation"
],
"Effect": "Allow",
"Resource": [
"arn:aws:s3:::example-nix-cache",
"arn:aws:s3:::example-nix-cache/*"
],
"Principal": "*"
}
]
}
For AWS S3 the binary cache URL for example bucket will be exactly s3://example-nix-cache.
Nix will use the default credential provider chain for authenticating requests to Amazon S3.
Nix supports authenticated reads from Amazon S3 and S3 compatible binary caches.
Your bucket will need a bucket policy allowing the desired users to perform the s3:GetObject and s3:GetBucketLocation action on all objects in the bucket. The anonymous policy in Section 13.4.1, “Anonymous Reads to your S3-compatible binary cache” can be updated to have a restricted Principal to support this.
Nix support fully supports writing to Amazon S3 and S3 compatible buckets. The binary cache URL for our example bucket will be s3://example-nix-cache.
Nix will use the default credential provider chain for authenticating requests to Amazon S3.
Your account will need the following IAM policy to upload to the cache:
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "UploadToCache",
"Effect": "Allow",
"Action": [
"s3:AbortMultipartUpload",
"s3:GetBucketLocation",
"s3:GetObject",
"s3:ListBucket",
"s3:ListBucketMultipartUploads",
"s3:ListMultipartUploadParts",
"s3:ListObjects",
"s3:PutObject"
],
"Resource": [
"arn:aws:s3:::example-nix-cache",
"arn:aws:s3:::example-nix-cache/*"
]
}
]
}
Example 13.1. Uploading with a specific credential profile for Amazon S3
nix copy --to 's3://example-nix-cache?profile=cache-upload®ion=eu-west-2' nixpkgs.hello
Example 13.2. Uploading to an S3-Compatible Binary Cache
nix copy --to 's3://example-nix-cache?profile=cache-upload&endpoint=minio.example.com' nixpkgs.hello
This chapter shows you how to write Nix expressions, which instruct Nix how to build packages. It starts with a simple example (a Nix expression for GNU Hello), and then moves on to a more in-depth look at the Nix expression language.
This section shows how to add and test the GNU Hello package to the Nix Packages collection. Hello is a program that prints out the text “Hello, world!”.
To add a package to the Nix Packages collection, you generally need to do three things:
Write a Nix expression for the package. This is a file that describes all the inputs involved in building the package, such as dependencies, sources, and so on.
Write a builder. This is a shell script[2] that actually builds the package from the inputs.
Add the package to the file pkgs/top-level/all-packages.nix. The Nix expression written in the first step is a function; it requires other packages in order to build it. In this step you put it all together, i.e., you call the function with the right arguments to build the actual package.
Example 14.1, “Nix expression for GNU Hello (default.nix)” shows a Nix expression for GNU Hello. It's actually already in the Nix Packages collection in pkgs/applications/misc/hello/ex-1/default.nix. It is customary to place each package in a separate directory and call the single Nix expression in that directory default.nix. The file has the following elements (referenced from the figure by number):
| This states that the expression is a function that expects to be called with three arguments: Nix functions generally have the form |
| So we have to build a package. Building something from other stuff is called a derivation in Nix (as opposed to sources, which are built by humans instead of computers). We perform a derivation by calling |
| The attribute |
| The attribute |
| The builder has to know what the sources of the package are. Here, the attribute Instead of |
| Since the derivation requires Perl, we have to pass the value of the perl = perl; will do the trick: it binds an attribute |
Example 14.2, “Build script for GNU Hello (builder.sh)” shows the builder referenced from Hello's Nix expression (stored in pkgs/applications/misc/hello/ex-1/builder.sh). The builder can actually be made a lot shorter by using the generic builder functions provided by stdenv, but here we write out the build steps to elucidate what a builder does. It performs the following steps:
| When Nix runs a builder, it initially completely clears the environment (except for the attributes declared in the derivation). For instance, the So the first step is to set up the environment. This is done by calling the |
| Since Hello needs Perl, we have to make sure that Perl is in the |
| Now we have to unpack the sources. The The whole build is performed in a temporary directory created in |
| GNU Hello is a typical Autoconf-based package, so we first have to run its |
| Finally we build Hello ( |
If you are wondering about the absence of error checking on the result of various commands called in the builder: this is because the shell script is evaluated with Bash's -e option, which causes the script to be aborted if any command fails without an error check.
The Nix expression in Example 14.1, “Nix expression for GNU Hello (default.nix)” is a function; it is missing some arguments that have to be filled in somewhere. In the Nix Packages collection this is done in the file pkgs/top-level/all-packages.nix, where all Nix expressions for packages are imported and called with the appropriate arguments. Example 14.3, “Composing GNU Hello (all-packages.nix)” shows some fragments of all-packages.nix.
| This file defines a set of attributes, all of which are concrete derivations (i.e., not functions). In fact, we define a mutually recursive set of attributes. That is, the attributes can refer to each other. This is precisely what we want since we want to “plug” the various packages into each other. |
| Here we import the Nix expression for GNU Hello. The import operation just loads and returns the specified Nix expression. In fact, we could just have put the contents of Example 14.1, “Nix expression for GNU Hello ( Note that we refer to |
| This is where the actual composition takes place. Here we call the function imported from The result of this function call is an actual derivation that can be built by Nix (since when we fill in the arguments of the function, what we get is its body, which is the call to NoteNixpkgs has a convenience function hello = callPackage ../applications/misc/hello/ex-1 { };
If necessary, you can set or override arguments: hello = callPackage ../applications/misc/hello/ex-1 { stdenv = myStdenv; };
|
| Likewise, we have to instantiate Perl, |
You can now try to build Hello. Of course, you could do nix-env -i hello, but you may not want to install a possibly broken package just yet. The best way to test the package is by using the command nix-build, which builds a Nix expression and creates a symlink named result in the current directory:
$ nix-build -A hello
building path `/nix/store/632d2b22514d...-hello-2.1.1'
hello-2.1.1/
hello-2.1.1/intl/
hello-2.1.1/intl/ChangeLog
...
$ ls -l result
lrwxrwxrwx ... 2006-09-29 10:43 result -> /nix/store/632d2b22514d...-hello-2.1.1
$ ./result/bin/hello
Hello, world! The -A option selects the hello attribute. This is faster than using the symbolic package name specified by the name attribute (which also happens to be hello) and is unambiguous (there can be multiple packages with the symbolic name hello, but there can be only one attribute in a set named hello).
nix-build registers the ./result symlink as a garbage collection root, so unless and until you delete the ./result symlink, the output of the build will be safely kept on your system. You can use nix-build’s -o switch to give the symlink another name.
Nix has a transactional semantics. Once a build finishes successfully, Nix makes a note of this in its database: it registers that the path denoted by out is now “valid”. If you try to build the derivation again, Nix will see that the path is already valid and finish immediately. If a build fails, either because it returns a non-zero exit code, because Nix or the builder are killed, or because the machine crashes, then the output paths will not be registered as valid. If you try to build the derivation again, Nix will remove the output paths if they exist (e.g., because the builder died half-way through make install) and try again. Note that there is no “negative caching”: Nix doesn't remember that a build failed, and so a failed build can always be repeated. This is because Nix cannot distinguish between permanent failures (e.g., a compiler error due to a syntax error in the source) and transient failures (e.g., a disk full condition).
Nix also performs locking. If you run multiple Nix builds simultaneously, and they try to build the same derivation, the first Nix instance that gets there will perform the build, while the others block (or perform other derivations if available) until the build finishes:
$ nix-build -A hello waiting for lock on `/nix/store/0h5b7hp8d4hqfrw8igvx97x1xawrjnac-hello-2.1.1x'
So it is always safe to run multiple instances of Nix in parallel (which isn’t the case with, say, make).
If you have a system with multiple CPUs, you may want to have Nix build different derivations in parallel (insofar as possible). Just pass the option -j , where NN is the maximum number of jobs to be run in parallel, or set. Typically this should be the number of CPUs.
Recall from Example 14.2, “Build script for GNU Hello (builder.sh)” that the builder looked something like this:
PATH=$perl/bin:$PATH tar xvfz $src cd hello-* ./configure --prefix=$out make make install
The builders for almost all Unix packages look like this — set up some environment variables, unpack the sources, configure, build, and install. For this reason the standard environment provides some Bash functions that automate the build process. A builder using the generic build facilities in shown in Example 14.4, “Build script using the generic build functions”.
| The |
| The function |
| The final step calls the shell function |
Discerning readers will note that the buildInputs could just as well have been set in the Nix expression, like this:
buildInputs = [ perl ];
The perl attribute can then be removed, and the builder becomes even shorter:
source $stdenv/setup genericBuild
In fact, mkDerivation provides a default builder that looks exactly like that, so it is actually possible to omit the builder for Hello entirely.
[2] In fact, it can be written in any language, but typically it's a bash shell script.
[3] Actually, it's initialised to /path-not-set to prevent Bash from setting it to a default value.
[4] How does it work? setup tries to source the file pkg/nix-support/setup-hookPERL5LIB environment variable to contain the lib/site_perl directories of all inputs.
The Nix expression language is a pure, lazy, functional language. Purity means that operations in the language don't have side-effects (for instance, there is no variable assignment). Laziness means that arguments to functions are evaluated only when they are needed. Functional means that functions are “normal” values that can be passed around and manipulated in interesting ways. The language is not a full-featured, general purpose language. Its main job is to describe packages, compositions of packages, and the variability within packages.
This section presents the various features of the language.
Nix has the following basic data types:
Strings can be written in three ways.
The most common way is to enclose the string between double quotes, e.g., "foo bar". Strings can span multiple lines. The special characters " and \ and the character sequence ${ must be escaped by prefixing them with a backslash (\). Newlines, carriage returns and tabs can be written as \n, \r and \t, respectively.
You can include the result of an expression into a string by enclosing it in ${, a feature known as antiquotation. The enclosed expression must evaluate to something that can be coerced into a string (meaning that it must be a string, a path, or a derivation). For instance, rather than writing ...}
"--with-freetype2-library=" + freetype + "/lib"
(where freetype is a derivation), you can instead write the more natural
"--with-freetype2-library=${freetype}/lib"The latter is automatically translated to the former. A more complicated example (from the Nix expression for Qt):
configureFlags = "
-system-zlib -system-libpng -system-libjpeg
${if openglSupport then "-dlopen-opengl
-L${mesa}/lib -I${mesa}/include
-L${libXmu}/lib -I${libXmu}/include" else ""}
${if threadSupport then "-thread" else "-no-thread"}
"; Note that Nix expressions and strings can be arbitrarily nested; in this case the outer string contains various antiquotations that themselves contain strings (e.g., "-thread"), some of which in turn contain expressions (e.g., ${mesa}).
The second way to write string literals is as an indented string, which is enclosed between pairs of double single-quotes, like so:
''
This is the first line.
This is the second line.
This is the third line.
''This kind of string literal intelligently strips indentation from the start of each line. To be precise, it strips from each line a number of spaces equal to the minimal indentation of the string as a whole (disregarding the indentation of empty lines). For instance, the first and second line are indented two space, while the third line is indented four spaces. Thus, two spaces are stripped from each line, so the resulting string is
"This is the first line.\nThis is the second line.\n This is the third line.\n"
Note that the whitespace and newline following the opening '' is ignored if there is no non-whitespace text on the initial line.
Antiquotation (${) is supported in indented strings.expr}
Since ${ and '' have special meaning in indented strings, you need a way to quote them. $ can be escaped by prefixing it with '' (that is, two single quotes), i.e., ''$. '' can be escaped by prefixing it with ', i.e., '''. $ removes any special meaning from the following $. Linefeed, carriage-return and tab characters can be written as ''\n, ''\r, ''\t, and ''\ escapes any other character.
Indented strings are primarily useful in that they allow multi-line string literals to follow the indentation of the enclosing Nix expression, and that less escaping is typically necessary for strings representing languages such as shell scripts and configuration files because '' is much less common than ". Example:
stdenv.mkDerivation {
...
postInstall =
''
mkdir $out/bin $out/etc
cp foo $out/bin
echo "Hello World" > $out/etc/foo.conf
${if enableBar then "cp bar $out/bin" else ""}
'';
...
}
Finally, as a convenience, URIs as defined in appendix B of RFC 2396 can be written as is, without quotes. For instance, the string "http://example.org/foo.tar.bz2" can also be written as http://example.org/foo.tar.bz2.
Numbers, which can be integers (like 123) or floating point (like 123.43 or .27e13).
Numbers are type-compatible: pure integer operations will always return integers, whereas any operation involving at least one floating point number will have a floating point number as a result.
Paths, e.g., /bin/sh or ./builder.sh. A path must contain at least one slash to be recognised as such; for instance, builder.sh is not a path[5]. If the file name is relative, i.e., if it does not begin with a slash, it is made absolute at parse time relative to the directory of the Nix expression that contained it. For instance, if a Nix expression in /foo/bar/bla.nix refers to ../xyzzy/fnord.nix, the absolute path is /foo/xyzzy/fnord.nix.
If the first component of a path is a ~, it is interpreted as if the rest of the path were relative to the user's home directory. e.g. ~/foo would be equivalent to /home/edolstra/foo for a user whose home directory is /home/edolstra.
Paths can also be specified between angle brackets, e.g. <nixpkgs>. This means that the directories listed in the environment variable NIX_PATH will be searched for the given file or directory name.
Booleans with values true and false.
The null value, denoted as null.
Lists are formed by enclosing a whitespace-separated list of values between square brackets. For example,
[ 123 ./foo.nix "abc" (f { x = y; }) ] defines a list of four elements, the last being the result of a call to the function f. Note that function calls have to be enclosed in parentheses. If they had been omitted, e.g.,
[ 123 ./foo.nix "abc" f { x = y; } ]the result would be a list of five elements, the fourth one being a function and the fifth being a set.
Note that lists are only lazy in values, and they are strict in length.
Sets are really the core of the language, since ultimately the Nix language is all about creating derivations, which are really just sets of attributes to be passed to build scripts.
Sets are just a list of name/value pairs (called attributes) enclosed in curly brackets, where each value is an arbitrary expression terminated by a semicolon. For example:
{ x = 123;
text = "Hello";
y = f { bla = 456; };
} This defines a set with attributes named x, text, y. The order of the attributes is irrelevant. An attribute name may only occur once.
Attributes can be selected from a set using the . operator. For instance,
{ a = "Foo"; b = "Bar"; }.a evaluates to "Foo". It is possible to provide a default value in an attribute selection using the or keyword. For example,
{ a = "Foo"; b = "Bar"; }.c or "Xyzzy" will evaluate to "Xyzzy" because there is no c attribute in the set.
You can use arbitrary double-quoted strings as attribute names:
{ "foo ${bar}" = 123; "nix-1.0" = 456; }."foo ${bar}"
This will evaluate to 123 (Assuming bar is antiquotable). In the case where an attribute name is just a single antiquotation, the quotes can be dropped:
{ foo = 123; }.${bar} or 456 This will evaluate to 123 if bar evaluates to "foo" when coerced to a string and 456 otherwise (again assuming bar is antiquotable).
In the special case where an attribute name inside of a set declaration evaluates to null (which is normally an error, as null is not antiquotable), that attribute is simply not added to the set:
{ ${if foo then "bar" else null} = true; } This will evaluate to {} if foo evaluates to false.
A set that has a __functor attribute whose value is callable (i.e. is itself a function or a set with a __functor attribute whose value is callable) can be applied as if it were a function, with the set itself passed in first , e.g.,
let add = { __functor = self: x: x + self.x; };
inc = add // { x = 1; };
in inc 1
evaluates to 2. This can be used to attach metadata to a function without the caller needing to treat it specially, or to implement a form of object-oriented programming, for example.
Recursive sets are just normal sets, but the attributes can refer to each other. For example,
rec {
x = y;
y = 123;
}.x
evaluates to 123. Note that without rec the binding x = y; would refer to the variable y in the surrounding scope, if one exists, and would be invalid if no such variable exists. That is, in a normal (non-recursive) set, attributes are not added to the lexical scope; in a recursive set, they are.
Recursive sets of course introduce the danger of infinite recursion. For example,
rec {
x = y;
y = x;
}.xdoes not terminate[6].
A let-expression allows you define local variables for an expression. For instance,
let x = "foo"; y = "bar"; in x + y
evaluates to "foobar".
When defining a set or in a let-expression it is often convenient to copy variables from the surrounding lexical scope (e.g., when you want to propagate attributes). This can be shortened using the inherit keyword. For instance,
let x = 123; in
{ inherit x;
y = 456;
}is equivalent to
let x = 123; in
{ x = x;
y = 456;
} and both evaluate to { x = 123; y = 456; }. (Note that this works because x is added to the lexical scope by the let construct.) It is also possible to inherit attributes from another set. For instance, in this fragment from all-packages.nix,
graphviz = (import ../tools/graphics/graphviz) {
inherit fetchurl stdenv libpng libjpeg expat x11 yacc;
inherit (xlibs) libXaw;
};
xlibs = {
libX11 = ...;
libXaw = ...;
...
}
libpng = ...;
libjpg = ...;
... the set used in the function call to the function defined in ../tools/graphics/graphviz inherits a number of variables from the surrounding scope (fetchurl ... yacc), but also inherits libXaw (the X Athena Widgets) from the xlibs (X11 client-side libraries) set.
Summarizing the fragment
... inherit x y z; inherit (src-set) a b c; ...
is equivalent to
... x = x; y = y; z = z; a = src-set.a; b = src-set.b; c = src-set.c; ...
when used while defining local variables in a let-expression or while defining a set.
Functions have the following form:
pattern:body
The pattern specifies what the argument of the function must look like, and binds variables in the body to (parts of) the argument. There are three kinds of patterns:
If a pattern is a single identifier, then the function matches any argument. Example:
let negate = x: !x;
concat = x: y: x + y;
in if negate true then concat "foo" "bar" else "" Note that concat is a function that takes one argument and returns a function that takes another argument. This allows partial parameterisation (i.e., only filling some of the arguments of a function); e.g.,
map (concat "foo") [ "bar" "bla" "abc" ]
evaluates to [ "foobar" "foobla" "fooabc" ].
A set pattern of the form { name1, name2, …, nameN } matches a set containing the listed attributes, and binds the values of those attributes to variables in the function body. For example, the function
{ x, y, z }: z + y + x can only be called with a set containing exactly the attributes x, y and z. No other attributes are allowed. If you want to allow additional arguments, you can use an ellipsis (...):
{ x, y, z, ... }: z + y + xThis works on any set that contains at least the three named attributes.
It is possible to provide default values for attributes, in which case they are allowed to be missing. A default value is specified by writing name ? ee is an arbitrary expression. For example,
{ x, y ? "foo", z ? "bar" }: z + y + x specifies a function that only requires an attribute named x, but optionally accepts y and z.
An @-pattern provides a means of referring to the whole value being matched:
args@{ x, y, z, ... }: z + y + x + args.abut can also be written as:
{ x, y, z, ... } @ args: z + y + x + args.a Here args is bound to the entire argument, which is further matched against the pattern { x, y, z, ... }. @-pattern makes mainly sense with an ellipsis(...) as you can access attribute names as a, using args.a, which was given as an additional attribute to the function.
Note that functions do not have names. If you want to give them a name, you can bind them to an attribute, e.g.,
let concat = { x, y }: x + y;
in concat { x = "foo"; y = "bar"; }
Conditionals look like this:
ife1thene2elsee3
where e1 is an expression that should evaluate to a Boolean value (true or false).
Assertions are generally used to check that certain requirements on or between features and dependencies hold. They look like this:
asserte1;e2
where e1 is an expression that should evaluate to a Boolean value. If it evaluates to true, e2 is returned; otherwise expression evaluation is aborted and a backtrace is printed.
Example 15.1. Nix expression for Subversion
{ localServer ? false
, httpServer ? false
, sslSupport ? false
, pythonBindings ? false
, javaSwigBindings ? false
, javahlBindings ? false
, stdenv, fetchurl
, openssl ? null, httpd ? null, db4 ? null, expat, swig ? null, j2sdk ? null
}:
assert localServer -> db4 != null; 
assert httpServer -> httpd != null && httpd.expat == expat; 
assert sslSupport -> openssl != null && (httpServer -> httpd.openssl == openssl); 
assert pythonBindings -> swig != null && swig.pythonSupport;
assert javaSwigBindings -> swig != null && swig.javaSupport;
assert javahlBindings -> j2sdk != null;
stdenv.mkDerivation {
name = "subversion-1.1.1";
...
openssl = if sslSupport then openssl else null; 
...
}Example 15.1, “Nix expression for Subversion” show how assertions are used in the Nix expression for Subversion.
| This assertion states that if Subversion is to have support for local repositories, then Berkeley DB is needed. So if the Subversion function is called with the |
| This is a more subtle condition: if Subversion is built with Apache ( |
| This assertion says that in order for Subversion to have SSL support (so that it can access |
| The conditional here is not really related to assertions, but is worth pointing out: it ensures that if SSL support is disabled, then the Subversion derivation is not dependent on OpenSSL, even if a non- |
A with-expression,
withe1;e2
introduces the set e1 into the lexical scope of the expression e2. For instance,
let as = { x = "foo"; y = "bar"; };
in with as; x + y evaluates to "foobar" since the with adds the x and y attributes of as to the lexical scope in the expression x + y. The most common use of with is in conjunction with the import function. E.g.,
with (import ./definitions.nix); ...
makes all attributes defined in the file definitions.nix available as if they were defined locally in a let-expression.
The bindings introduced by with do not shadow bindings introduced by other means, e.g.
let a = 3; in with { a = 1; }; let a = 4; in with { a = 2; }; ...establishes the same scope as
let a = 1; in let a = 2; in let a = 3; in let a = 4; in ...
Table 15.1, “Operators” lists the operators in the Nix expression language, in order of precedence (from strongest to weakest binding).
Table 15.1. Operators
| Syntax | Associativity | Description |
|---|---|---|
e . attrpath [ or def ] | none | Select attribute denoted by the attribute path attrpath from set e. (An attribute path is a dot-separated list of attribute names.) If the attribute doesn’t exist, return def if provided, otherwise abort evaluation. |
e1 e2 | left | Call function e1 with argument e2. |
- e | none | Arithmetic negation. |
e ? attrpath | none | Test whether set e contains the attribute denoted by attrpath; return true or false. |
e1 ++ e2 | right | List concatenation. |
e1 * e2, e1 / e2 | left | Arithmetic multiplication and division. |
e1 + e2, e1 - e2 | left | Arithmetic addition and subtraction. String or path concatenation (only by +). |
! e | none | Boolean negation. |
e1 // e2 | right | Return a set consisting of the attributes in e1 and e2 (with the latter taking precedence over the former in case of equally named attributes). |
e1 < e2, e1 > e2, e1 <= e2, e1 >= e2 | none | Arithmetic comparison. |
e1 == e2, e1 != e2 | none | Equality and inequality. |
e1 && e2 | left | Logical AND. |
e1 || e2 | left | Logical OR. |
e1 -> e2 | none | Logical implication (equivalent to !). |
The most important built-in function is derivation, which is used to describe a single derivation (a build action). It takes as input a set, the attributes of which specify the inputs of the build.
There must be an attribute named system whose value must be a string specifying a Nix platform identifier, such as "i686-linux" or "x86_64-darwin"[7] The build can only be performed on a machine and operating system matching the platform identifier. (Nix can automatically forward builds for other platforms by forwarding them to other machines; see Chapter 16, Remote Builds.)
There must be an attribute named name whose value must be a string. This is used as a symbolic name for the package by nix-env, and it is appended to the output paths of the derivation.
There must be an attribute named builder that identifies the program that is executed to perform the build. It can be either a derivation or a source (a local file reference, e.g., ./builder.sh).
Every attribute is passed as an environment variable to the builder. Attribute values are translated to environment variables as follows:
Strings and numbers are just passed verbatim.
A path (e.g., ../foo/sources.tar) causes the referenced file to be copied to the store; its location in the store is put in the environment variable. The idea is that all sources should reside in the Nix store, since all inputs to a derivation should reside in the Nix store.
A derivation causes that derivation to be built prior to the present derivation; its default output path is put in the environment variable.
Lists of the previous types are also allowed. They are simply concatenated, separated by spaces.
true is passed as the string 1, false and null are passed as an empty string.
The optional attribute args specifies command-line arguments to be passed to the builder. It should be a list.
The optional attribute outputs specifies a list of symbolic outputs of the derivation. By default, a derivation produces a single output path, denoted as out. However, derivations can produce multiple output paths. This is useful because it allows outputs to be downloaded or garbage-collected separately. For instance, imagine a library package that provides a dynamic library, header files, and documentation. A program that links against the library doesn’t need the header files and documentation at runtime, and it doesn’t need the documentation at build time. Thus, the library package could specify:
outputs = [ "lib" "headers" "doc" ];
This will cause Nix to pass environment variables lib, headers and doc to the builder containing the intended store paths of each output. The builder would typically do something like
./configure --libdir=$lib/lib --includedir=$headers/include --docdir=$doc/share/doc
for an Autoconf-style package. You can refer to each output of a derivation by selecting it as an attribute, e.g.
buildInputs = [ pkg.lib pkg.headers ];
The first element of outputs determines the default output. Thus, you could also write
buildInputs = [ pkg pkg.headers ];
since pkg is equivalent to pkg.lib.
The function mkDerivation in the Nixpkgs standard environment is a wrapper around derivation that adds a default value for system and always uses Bash as the builder, to which the supplied builder is passed as a command-line argument. See the Nixpkgs manual for details.
The builder is executed as follows:
A temporary directory is created under the directory specified by TMPDIR (default /tmp) where the build will take place. The current directory is changed to this directory.
The environment is cleared and set to the derivation attributes, as specified above.
In addition, the following variables are set:
NIX_BUILD_TOP contains the path of the temporary directory for this build.
Also, TMPDIR, TEMPDIR, TMP, TEMP are set to point to the temporary directory. This is to prevent the builder from accidentally writing temporary files anywhere else. Doing so might cause interference by other processes.
PATH is set to /path-not-set to prevent shells from initialising it to their built-in default value.
HOME is set to /homeless-shelter to prevent programs from using /etc/passwd or the like to find the user's home directory, which could cause impurity. Usually, when HOME is set, it is used as the location of the home directory, even if it points to a non-existent path.
NIX_STORE is set to the path of the top-level Nix store directory (typically, /nix/store).
For each output declared in outputs, the corresponding environment variable is set to point to the intended path in the Nix store for that output. Each output path is a concatenation of the cryptographic hash of all build inputs, the name attribute and the output name. (The output name is omitted if it’s out.)
If an output path already exists, it is removed. Also, locks are acquired to prevent multiple Nix instances from performing the same build at the same time.
A log of the combined standard output and error is written to /nix/var/log/nix.
The builder is executed with the arguments specified by the attribute args. If it exits with exit code 0, it is considered to have succeeded.
The temporary directory is removed (unless the -K option was specified).
If the build was successful, Nix scans each output path for references to input paths by looking for the hash parts of the input paths. Since these are potential runtime dependencies, Nix registers them as dependencies of the output paths.
After the build, Nix sets the last-modified timestamp on all files in the build result to 1 (00:00:01 1/1/1970 UTC), sets the group to the default group, and sets the mode of the file to 0444 or 0555 (i.e., read-only, with execute permission enabled if the file was originally executable). Note that possible setuid and setgid bits are cleared. Setuid and setgid programs are not currently supported by Nix. This is because the Nix archives used in deployment have no concept of ownership information, and because it makes the build result dependent on the user performing the build.
Derivations can declare some infrequently used optional attributes.
allowedReferencesThe optional attribute allowedReferences specifies a list of legal references (dependencies) of the output of the builder. For example,
allowedReferences = [];
enforces that the output of a derivation cannot have any runtime dependencies on its inputs. To allow an output to have a runtime dependency on itself, use "out" as a list item. This is used in NixOS to check that generated files such as initial ramdisks for booting Linux don’t have accidental dependencies on other paths in the Nix store.
allowedRequisitesThis attribute is similar to allowedReferences, but it specifies the legal requisites of the whole closure, so all the dependencies recursively. For example,
allowedRequisites = [ foobar ];
enforces that the output of a derivation cannot have any other runtime dependency than foobar, and in addition it enforces that foobar itself doesn't introduce any other dependency itself.
disallowedReferencesThe optional attribute disallowedReferences specifies a list of illegal references (dependencies) of the output of the builder. For example,
disallowedReferences = [ foo ];
enforces that the output of a derivation cannot have a direct runtime dependencies on the derivation foo.
disallowedRequisitesThis attribute is similar to disallowedReferences, but it specifies illegal requisites for the whole closure, so all the dependencies recursively. For example,
disallowedRequisites = [ foobar ];
enforces that the output of a derivation cannot have any runtime dependency on foobar or any other derivation depending recursively on foobar.
exportReferencesGraphThis attribute allows builders access to the references graph of their inputs. The attribute is a list of inputs in the Nix store whose references graph the builder needs to know. The value of this attribute should be a list of pairs [ . The references graph of each name1 path1 name2 path2 ... ]pathN will be stored in a text file nameN in the temporary build directory. The text files have the format used by nix-store --register-validity (with the deriver fields left empty). For example, when the following derivation is built:
derivation {
...
exportReferencesGraph = [ "libfoo-graph" libfoo ];
};
the references graph of libfoo is placed in the file libfoo-graph in the temporary build directory.
exportReferencesGraph is useful for builders that want to do something with the closure of a store path. Examples include the builders in NixOS that generate the initial ramdisk for booting Linux (a cpio archive containing the closure of the boot script) and the ISO-9660 image for the installation CD (which is populated with a Nix store containing the closure of a bootable NixOS configuration).
impureEnvVarsThis attribute allows you to specify a list of environment variables that should be passed from the environment of the calling user to the builder. Usually, the environment is cleared completely when the builder is executed, but with this attribute you can allow specific environment variables to be passed unmodified. For example, fetchurl in Nixpkgs has the line
impureEnvVars = [ "http_proxy" "https_proxy" ... ];
to make it use the proxy server configuration specified by the user in the environment variables http_proxy and friends.
This attribute is only allowed in fixed-output derivations, where impurities such as these are okay since (the hash of) the output is known in advance. It is ignored for all other derivations.
impureEnvVars implementation takes environment variables from the current builder process. When a daemon is building its environmental variables are used. Without the daemon, the environmental variables come from the environment of the nix-build.outputHash, outputHashAlgo, outputHashModeThese attributes declare that the derivation is a so-called fixed-output derivation, which means that a cryptographic hash of the output is already known in advance. When the build of a fixed-output derivation finishes, Nix computes the cryptographic hash of the output and compares it to the hash declared with these attributes. If there is a mismatch, the build fails.
The rationale for fixed-output derivations is derivations such as those produced by the fetchurl function. This function downloads a file from a given URL. To ensure that the downloaded file has not been modified, the caller must also specify a cryptographic hash of the file. For example,
fetchurl {
url = http://ftp.gnu.org/pub/gnu/hello/hello-2.1.1.tar.gz;
sha256 = "1md7jsfd8pa45z73bz1kszpp01yw6x5ljkjk2hx7wl800any6465";
}
It sometimes happens that the URL of the file changes, e.g., because servers are reorganised or no longer available. We then must update the call to fetchurl, e.g.,
fetchurl {
url = ftp://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz;
sha256 = "1md7jsfd8pa45z73bz1kszpp01yw6x5ljkjk2hx7wl800any6465";
}
If a fetchurl derivation was treated like a normal derivation, the output paths of the derivation and all derivations depending on it would change. For instance, if we were to change the URL of the Glibc source distribution in Nixpkgs (a package on which almost all other packages depend) massive rebuilds would be needed. This is unfortunate for a change which we know cannot have a real effect as it propagates upwards through the dependency graph.
For fixed-output derivations, on the other hand, the name of the output path only depends on the outputHash* and name attributes, while all other attributes are ignored for the purpose of computing the output path. (The name attribute is included because it is part of the path.)
As an example, here is the (simplified) Nix expression for fetchurl:
{ stdenv, curl }: # The curl program is used for downloading.
{ url, md5 }:
stdenv.mkDerivation {
name = baseNameOf (toString url);
builder = ./builder.sh;
buildInputs = [ curl ];
# This is a fixed-output derivation; the output must be a regular
# file with MD5 hash md5.
outputHashMode = "flat";
outputHashAlgo = "md5";
outputHash = md5;
inherit url;
}
The outputHashAlgo attribute specifies the hash algorithm used to compute the hash. It can currently be "md5", "sha1" or "sha256".
The outputHashMode attribute determines how the hash is computed. It must be one of the following two values:
"flat"The output must be a non-executable regular file. If it isn’t, the build fails. The hash is simply computed over the contents of that file (so it’s equal to what Unix commands like md5sum or sha1sum produce).
This is the default.
"recursive"The hash is computed over the NAR archive dump of the output (i.e., the result of nix-store --dump). In this case, the output can be anything, including a directory tree.
The outputHash attribute, finally, must be a string containing the hash in either hexadecimal or base-32 notation. (See the nix-hash command for information about converting to and from base-32 notation.)
passAsFileA list of names of attributes that should be passed via files rather than environment variables. For example, if you have
passAsFile = ["big"];
big = "a very long string";
then when the builder runs, the environment variable bigPath will contain the absolute path to a temporary file containing a very long string. That is, for any attribute x listed in passAsFile, Nix will pass an environment variable xPathx. This is useful when you need to pass large strings to a builder, since most operating systems impose a limit on the size of the environment (typically, a few hundred kilobyte).
preferLocalBuildIf this attribute is set to true, it has two effects. First, the derivation will always be built, not substituted, even if a substitute is available. Second, if distributed building is enabled, then, if possible, the derivaton will be built locally instead of forwarded to a remote machine. This is appropriate for trivial builders where the cost of doing a download or remote build would exceed the cost of building locally.
This section lists the functions and constants built into the Nix expression evaluator. (The built-in function derivation is discussed above.) Some built-ins, such as derivation, are always in scope of every Nix expression; you can just access them right away. But to prevent polluting the namespace too much, most built-ins are not in scope. Instead, you can access them through the builtins built-in value, which is a set that contains all built-in functions and values. For instance, derivation is also available as builtins.derivation.
abort sAbort Nix expression evaluation, print error message s.
builtins.add e1 e2Return the sum of the numbers e1 and e2.
builtins.all pred listReturn true if the function pred returns true for all elements of list, and false otherwise.
builtins.any pred listReturn true if the function pred returns true for at least one element of list, and false otherwise.
builtins.attrNames setReturn the names of the attributes in the set set in an alphabetically sorted list. For instance, builtins.attrNames { y = 1; x = "foo"; } evaluates to [ "x" "y" ].
builtins.attrValues setReturn the values of the attributes in the set set in the order corresponding to the sorted attribute names.
baseNameOf sReturn the base name of the string s, that is, everything following the final slash in the string. This is similar to the GNU basename command.
builtins.bitAnd e1 e2Return the bitwise AND of the integers e1 and e2.
builtins.bitOr e1 e2Return the bitwise OR of the integers e1 and e2.
builtins.bitXor e1 e2Return the bitwise XOR of the integers e1 and e2.
builtinsThe set builtins contains all the built-in functions and values. You can use builtins to test for the availability of features in the Nix installation, e.g.,
if builtins ? getEnv then builtins.getEnv "PATH" else ""
This allows a Nix expression to fall back gracefully on older Nix installations that don’t have the desired built-in function.
builtins.compareVersions s1 s2Compare two strings representing versions and return -1 if version s1 is older than version s2, 0 if they are the same, and 1 if s1 is newer than s2. The version comparison algorithm is the same as the one used by nix-env -u.
builtins.splitVersion sSplit a string representing a version into its components, by the same version splitting logic underlying the version comparison in nix-env -u.
builtins.concatLists listsConcatenate a list of lists into a single list.
builtins.concatStringsSep separator listConcatenate a list of strings with a separator between each element, e.g. concatStringsSep "/" ["usr" "local" "bin"] == "usr/local/bin"
builtins.currentSystemThe built-in value currentSystem evaluates to the Nix platform identifier for the Nix installation on which the expression is being evaluated, such as "i686-linux" or "x86_64-darwin".
builtins.deepSeq e1 e2This is like seq , except that e1 e2e1 is evaluated deeply: if it’s a list or set, its elements or attributes are also evaluated recursively.
derivation attrsderivation is described in Section 15.4, “Derivations”.
dirOf sReturn the directory part of the string s, that is, everything before the final slash in the string. This is similar to the GNU dirname command.
builtins.div e1 e2Return the quotient of the numbers e1 and e2.
builtins.elem x xsReturn true if a value equal to x occurs in the list xs, and false otherwise.
builtins.elemAt xs nReturn element n from the list xs. Elements are counted starting from 0. A fatal error occurs in the index is out of bounds.
builtins.fetchurl urlDownload the specified URL and return the path of the downloaded file. This function is not available if restricted evaluation mode is enabled.
fetchTarball urlDownload the specified URL, unpack it and return the path of the unpacked tree. The file must be a tape archive (.tar) compressed with gzip, bzip2 or xz. The top-level path component of the files in the tarball is removed, so it is best if the tarball contains a single directory at top level. The typical use of the function is to obtain external Nix expression dependencies, such as a particular version of Nixpkgs, e.g.
with import (fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz) {};
stdenv.mkDerivation { … }
The fetched tarball is cached for a certain amount of time (1 hour by default) in ~/.cache/nix/tarballs/. You can change the cache timeout either on the command line with --option tarball-ttl or in the Nix configuration file with this option: number of secondstarball-ttl . number of seconds to cache
Note that when obtaining the hash with nix-prefetch-url the option --unpack is required.
This function can also verify the contents against a hash. In that case, the function takes a set instead of a URL. The set requires the attribute url and the attribute sha256, e.g.
with import (fetchTarball {
url = https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz;
sha256 = "1jppksrfvbk5ypiqdz4cddxdl8z6zyzdb2srq8fcffr327ld5jj2";
}) {};
stdenv.mkDerivation { … }
This function is not available if restricted evaluation mode is enabled.
builtins.fetchGit args Fetch a path from git. args can be a URL, in which case the HEAD of the repo at that URL is fetched. Otherwise, it can be an attribute with the following attributes (all except url optional):
The URL of the repo.
The name of the directory the repo should be exported to in the store. Defaults to the basename of the URL.
The git revision to fetch. Defaults to the tip of ref.
The git ref to look for the requested revision under. This is often a branch or tag name. Defaults to HEAD.
Example 15.2. Fetching a private repository over SSH
builtins.fetchGit {
url = "git@github.com:my-secret/repository.git";
ref = "master";
rev = "adab8b916a45068c044658c4158d81878f9ed1c3";
}Example 15.3. Fetching a repository's specific commit on an arbitrary branch
If the revision you're looking for is in the default branch of the gift repository you don't strictly need to specify the branch name in the ref attribute.
However, if the revision you're looking for is in a future branch for the non-default branch you will need to specify the the ref attribute as well.
builtins.fetchGit {
url = "https://github.com/nixos/nix.git";
rev = "841fcbd04755c7a2865c51c1e2d3b045976b7452";
ref = "1.11-maintenance";
}Example 15.4. Fetching a repository's specific commit on the default branch
If the revision you're looking for is in the default branch of the gift repository you may omit the ref attribute.
builtins.fetchGit {
url = "https://github.com/nixos/nix.git";
rev = "841fcbd04755c7a2865c51c1e2d3b045976b7452";
}Example 15.5. Fetching a tag
builtins.fetchGit {
url = "https://github.com/nixos/nix.git";
ref = "tags/1.9";
}Example 15.6. Fetching the latest version of a remote branch
builtins.fetchGit can behave impurely fetch the latest version of a remote branch.
tarball-ttl.builtins.fetchGit {
url = "ssh://git@github.com/nixos/nix.git";
ref = "master";
}builtins.filter f xsReturn a list consisting of the elements of xs for which the function f returns true.
builtins.filterSource e1 e2This function allows you to copy sources into the Nix store while filtering certain files. For instance, suppose that you want to use the directory source-dir as an input to a Nix expression, e.g.
stdenv.mkDerivation {
...
src = ./source-dir;
}
However, if source-dir is a Subversion working copy, then all those annoying .svn subdirectories will also be copied to the store. Worse, the contents of those directories may change a lot, causing lots of spurious rebuilds. With filterSource you can filter out the .svn directories:
src = builtins.filterSource
(path: type: type != "directory" || baseNameOf path != ".svn")
./source-dir;
Thus, the first argument e1 must be a predicate function that is called for each regular file, directory or symlink in the source tree e2. If the function returns true, the file is copied to the Nix store, otherwise it is omitted. The function is called with two arguments. The first is the full path of the file. The second is a string that identifies the type of the file, which is either "regular", "directory", "symlink" or "unknown" (for other kinds of files such as device nodes or fifos — but note that those cannot be copied to the Nix store, so if the predicate returns true for them, the copy will fail). If you exclude a directory, the entire corresponding subtree of e2 will be excluded.
builtins.foldl’ op nul listReduce a list by applying a binary operator, from left to right, e.g. foldl’ op nul [x0 x1 x2 ...] = op (op (op nul x0) x1) x2) .... The operator is applied strictly, i.e., its arguments are evaluated first. For example, foldl’ (x: y: x + y) 0 [1 2 3] evaluates to 6.
builtins.functionArgs f Return a set containing the names of the formal arguments expected by the function f. The value of each attribute is a Boolean denoting whether the corresponding argument has a default value. For instance, functionArgs ({ x, y ? 123}: ...) = { x = false; y = true; }.
"Formal argument" here refers to the attributes pattern-matched by the function. Plain lambdas are not included, e.g. functionArgs (x: ...) = { }.
builtins.fromJSON eConvert a JSON string to a Nix value. For example,
builtins.fromJSON ''{"x": [1, 2, 3], "y": null}''
returns the value { x = [ 1 2 3 ]; y = null; }.
builtins.genList generator lengthGenerate list of size length, with each element i equal to the value returned by generator i. For example,
builtins.genList (x: x * x) 5
returns the list [ 0 1 4 9 16 ].
builtins.getAttr s setgetAttr returns the attribute named s from set. Evaluation aborts if the attribute doesn’t exist. This is a dynamic version of the . operator, since s is an expression rather than an identifier.
builtins.getEnv sgetEnv returns the value of the environment variable s, or an empty string if the variable doesn’t exist. This function should be used with care, as it can introduce all sorts of nasty environment dependencies in your Nix expression.
getEnv is used in Nix Packages to locate the file ~/.nixpkgs/config.nix, which contains user-local settings for Nix Packages. (That is, it does a getEnv "HOME" to locate the user’s home directory.)
builtins.hasAttr s sethasAttr returns true if set has an attribute named s, and false otherwise. This is a dynamic version of the ? operator, since s is an expression rather than an identifier.
builtins.hashString type sReturn a base-16 representation of the cryptographic hash of string s. The hash algorithm specified by type must be one of "md5", "sha1" or "sha256".
builtins.head listReturn the first element of a list; abort evaluation if the argument isn’t a list or is an empty list. You can test whether a list is empty by comparing it with [].
import pathLoad, parse and return the Nix expression in the file path. If path is a directory, the file default.nix in that directory is loaded. Evaluation aborts if the file doesn’t exist or contains an incorrect Nix expression. import implements Nix’s module system: you can put any Nix expression (such as a set or a function) in a separate file, and use it from Nix expressions in other files.
A Nix expression loaded by import must not contain any free variables (identifiers that are not defined in the Nix expression itself and are not built-in). Therefore, it cannot refer to variables that are in scope at the call site. For instance, if you have a calling expression
rec {
x = 123;
y = import ./foo.nix;
} then the following foo.nix will give an error:
x + 456
since x is not in scope in foo.nix. If you want x to be available in foo.nix, you should pass it as a function argument:
rec {
x = 123;
y = import ./foo.nix x;
}and
x: x + 456
(The function argument doesn’t have to be called x in foo.nix; any name would work.)
builtins.intersectAttrs e1 e2Return a set consisting of the attributes in the set e2 that also exist in the set e1.
builtins.isAttrs eReturn true if e evaluates to a set, and false otherwise.
builtins.isList eReturn true if e evaluates to a list, and false otherwise.
builtins.isFunction eReturn true if e evaluates to a function, and false otherwise.
builtins.isString eReturn true if e evaluates to a string, and false otherwise.
builtins.isInt eReturn true if e evaluates to an int, and false otherwise.
builtins.isFloat eReturn true if e evaluates to a float, and false otherwise.
builtins.isBool eReturn true if e evaluates to a bool, and false otherwise.
isNull eReturn true if e evaluates to null, and false otherwise.
e == null instead.builtins.length eReturn the length of the list e.
builtins.lessThan e1 e2Return true if the number e1 is less than the number e2, and false otherwise. Evaluation aborts if either e1 or e2 does not evaluate to a number.
builtins.listToAttrs eConstruct a set from a list specifying the names and values of each attribute. Each element of the list should be a set consisting of a string-valued attribute name specifying the name of the attribute, and an attribute value specifying its value. Example:
builtins.listToAttrs
[ { name = "foo"; value = 123; }
{ name = "bar"; value = 456; }
]
evaluates to
{ foo = 123; bar = 456; }
map f listApply the function f to each element in the list list. For example,
map (x: "foo" + x) [ "bar" "bla" "abc" ]
evaluates to [ "foobar" "foobla" "fooabc" ].
builtins.match regex strReturns a list if the extended POSIX regular expression regex matches str precisely, otherwise returns null. Each item in the list is a regex group.
builtins.match "ab" "abc"
Evaluates to null.
builtins.match "abc" "abc"
Evaluates to [ ].
builtins.match "a(b)(c)" "abc"
Evaluates to [ "b" "c" ].
builtins.match "[[:space:]]+([[:upper:]]+)[[:space:]]+" " FOO "
Evaluates to [ "foo" ].
builtins.mul e1 e2Return the product of the numbers e1 and e2.
builtins.parseDrvName sSplit the string s into a package name and version. The package name is everything up to but not including the first dash followed by a digit, and the version is everything following that dash. The result is returned in a set { name, version }. Thus, builtins.parseDrvName "nix-0.12pre12876" returns { name = "nix"; version = "0.12pre12876"; }.
builtins.path args An enrichment of the built-in path type, based on the attributes present in args. All are optional except path:
The underlying path.
The name of the path when added to the store. This can used to reference paths that have nix-illegal characters in their names, like @.
A function of the type expected by builtins.filterSource, with the same semantics.
When false, when path is added to the store it is with a flat hash, rather than a hash of the NAR serialization of the file. Thus, path must refer to a regular file, not a directory. This allows similar behavior to fetchurl. Defaults to true.
When provided, this is the expected hash of the file at the path. Evaluation will fail if the hash is incorrect, and providing a hash allows builtins.path to be used even when the pure-eval nix config option is on.
builtins.pathExists pathReturn true if the path path exists, and false otherwise. One application of this function is to conditionally include a Nix expression containing user configuration:
let
fileName = builtins.getEnv "CONFIG_FILE";
config =
if fileName != "" && builtins.pathExists (builtins.toPath fileName)
then import (builtins.toPath fileName)
else { someSetting = false; }; # default configuration
in config.someSetting (Note that CONFIG_FILE must be an absolute path for this to work.)
builtins.readDir pathReturn the contents of the directory path as a set mapping directory entries to the corresponding file type. For instance, if directory A contains a regular file B and another directory C, then builtins.readDir ./A will return the set
{ B = "regular"; C = "directory"; } The possible values for the file type are "regular", "directory", "symlink" and "unknown".
builtins.readFile pathReturn the contents of the file path as a string.
removeAttrs set listRemove the attributes listed in list from set. The attributes don’t have to exist in set. For instance,
removeAttrs { x = 1; y = 2; z = 3; } [ "a" "x" "z" ] evaluates to { y = 2; }.
builtins.replaceStrings from to sGiven string s, replace every occurrence of the strings in from with the corresponding string in to. For example,
builtins.replaceStrings ["oo" "a"] ["a" "i"] "foobar"
evaluates to "fabir".
builtins.seq e1 e2Evaluate e1, then evaluate and return e2. This ensures that a computation is strict in the value of e1.
builtins.sort comparator listReturn list in sorted order. It repeatedly calls the function comparator with two elements. The comparator should return true if the first element is less than the second, and false otherwise. For example,
builtins.sort builtins.lessThan [ 483 249 526 147 42 77 ]
produces the list [ 42 77 147 249 483 526 ].
This is a stable sort: it preserves the relative order of elements deemed equal by the comparator.
builtins.split regex strReturns a list composed of non matched strings interleaved with the lists of the extended POSIX regular expression regex matches of str. Each item in the lists of matched sequences is a regex group.
builtins.split "(a)b" "abc"
Evaluates to [ "" [ "a" ] "c" ].
builtins.split "([ac])" "abc"
Evaluates to [ "" [ "a" ] "b" [ "c" ] "" ].
builtins.split "(a)|(c)" "abc"
Evaluates to [ "" [ "a" null ] "b" [ null "c" ] "" ].
builtins.split "([[:upper:]]+)" " FOO "
Evaluates to [ " " [ "FOO" ] " " ].
builtins.stringLength eReturn the length of the string e. If e is not a string, evaluation is aborted.
builtins.sub e1 e2Return the difference between the numbers e1 and e2.
builtins.substring start len sReturn the substring of s from character position start (zero-based) up to but not including start + len. If start is greater than the length of the string, an empty string is returned, and if start + len lies beyond the end of the string, only the substring up to the end of the string is returned. start must be non-negative. For example,
builtins.substring 0 3 "nixos"
evaluates to "nix".
builtins.tail listReturn the second to last elements of a list; abort evaluation if the argument isn’t a list or is an empty list.
throw sThrow an error message s. This usually aborts Nix expression evaluation, but in nix-env -qa and other commands that try to evaluate a set of derivations to get information about those derivations, a derivation that throws an error is silently skipped (which is not the case for abort).
builtins.toFile name sStore the string s in a file in the Nix store and return its path. The file has suffix name. This file can be used as an input to derivations. One application is to write builders “inline”. For instance, the following Nix expression combines Example 14.1, “Nix expression for GNU Hello (default.nix)” and Example 14.2, “Build script for GNU Hello (builder.sh)” into one file:
{ stdenv, fetchurl, perl }:
stdenv.mkDerivation {
name = "hello-2.1.1";
builder = builtins.toFile "builder.sh" "
source $stdenv/setup
PATH=$perl/bin:$PATH
tar xvfz $src
cd hello-*
./configure --prefix=$out
make
make install
";
src = fetchurl {
url = http://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz;
sha256 = "1md7jsfd8pa45z73bz1kszpp01yw6x5ljkjk2hx7wl800any6465";
};
inherit perl;
}
It is even possible for one file to refer to another, e.g.,
builder = let
configFile = builtins.toFile "foo.conf" "
# This is some dummy configuration file.
...
";
in builtins.toFile "builder.sh" "
source $stdenv/setup
...
cp ${configFile} $out/etc/foo.conf
"; Note that ${configFile} is an antiquotation (see Section 15.1, “Values”), so the result of the expression configFile (i.e., a path like /nix/store/m7p7jfny445k...-foo.conf) will be spliced into the resulting string.
It is however not allowed to have files mutually referring to each other, like so:
let
foo = builtins.toFile "foo" "...${bar}...";
bar = builtins.toFile "bar" "...${foo}...";
in foo This is not allowed because it would cause a cyclic dependency in the computation of the cryptographic hashes for foo and bar.
It is also not possible to reference the result of a derivation. If you are using Nixpkgs, the writeTextFile function is able to do that.
builtins.toJSON eReturn a string containing a JSON representation of e. Strings, integers, floats, booleans, nulls and lists are mapped to their JSON equivalents. Sets (except derivations) are represented as objects. Derivations are translated to a JSON string containing the derivation’s output path. Paths are copied to the store and represented as a JSON string of the resulting store path.
builtins.toPath sConvert the string value s into a path value. The string s must represent an absolute path (i.e., must start with /). The path need not exist. The resulting path is canonicalised, e.g., builtins.toPath "//foo/xyzzy/../bar/" returns /foo/bar.
toString eConvert the expression e to a string. e can be:
A string (in which case the string is returned unmodified).
A path (e.g., toString /foo/bar yields "/foo/bar".
A set containing { __toString = self: ...; }.
An integer.
A list, in which case the string representations of its elements are joined with spaces.
A Boolean (false yields "", true yields "1".
null, which yields the empty string.
builtins.toXML eReturn a string containing an XML representation of e. The main application for toXML is to communicate information with the builder in a more structured format than plain environment variables.
Example 15.7, “Passing information to a builder using toXML” shows an example where this is the case. The builder is supposed to generate the configuration file for a Jetty servlet container. A servlet container contains a number of servlets (*.war files) each exported under a specific URI prefix. So the servlet configuration is a list of sets containing the path and war of the servlet (). This kind of information is difficult to communicate with the normal method of passing information through an environment variable, which just concatenates everything together into a string (which might just work in this case, but wouldn’t work if fields are optional or contain lists themselves). Instead the Nix expression is converted to an XML representation with toXML, which is unambiguous and can easily be processed with the appropriate tools. For instance, in the example an XSLT stylesheet () is applied to it () to generate the XML configuration file for the Jetty server. The XML representation produced from by toXML is shown in Example 15.8, “XML representation produced by toXML”.
Note that Example 15.7, “Passing information to a builder using toXML” uses the toFile built-in to write the builder and the stylesheet “inline” in the Nix expression. The path of the stylesheet is spliced into the builder at xsltproc ${stylesheet} ....
Example 15.7. Passing information to a builder using toXML
{ stdenv, fetchurl, libxslt, jira, uberwiki }:
stdenv.mkDerivation (rec {
name = "web-server";
buildInputs = [ libxslt ];
builder = builtins.toFile "builder.sh" "
source $stdenv/setup
mkdir $out
echo $servlets | xsltproc ${stylesheet} - > $out/server-conf.xml
";
stylesheet = builtins.toFile "stylesheet.xsl"
"<?xml version='1.0' encoding='UTF-8'?>
<xsl:stylesheet xmlns:xsl='http://www.w3.org/1999/XSL/Transform' version='1.0'>
<xsl:template match='/'>
<Configure>
<xsl:for-each select='/expr/list/attrs'>
<Call name='addWebApplication'>
<Arg><xsl:value-of select=\"attr[@name = 'path']/string/@value\" /></Arg>
<Arg><xsl:value-of select=\"attr[@name = 'war']/path/@value\" /></Arg>
</Call>
</xsl:for-each>
</Configure>
</xsl:template>
</xsl:stylesheet>
";
servlets = builtins.toXML [
{ path = "/bugtracker"; war = jira + "/lib/atlassian-jira.war"; }
{ path = "/wiki"; war = uberwiki + "/uberwiki.war"; }
];
})Example 15.8. XML representation produced by toXML
<?xml version='1.0' encoding='utf-8'?>
<expr>
<list>
<attrs>
<attr name="path">
<string value="/bugtracker" />
</attr>
<attr name="war">
<path value="/nix/store/d1jh9pasa7k2...-jira/lib/atlassian-jira.war" />
</attr>
</attrs>
<attrs>
<attr name="path">
<string value="/wiki" />
</attr>
<attr name="war">
<path value="/nix/store/y6423b1yi4sx...-uberwiki/uberwiki.war" />
</attr>
</attrs>
</list>
</expr>builtins.trace e1 e2Evaluate e1 and print its abstract syntax representation on standard error. Then return e2. This function is useful for debugging.
builtins.tryEval eTry to evaluate e. Return a set containing the attributes success (true if e evaluated successfully, false if an error was thrown) and value, equalling e if successful and false otherwise.
builtins.typeOf eReturn a string representing the type of the value e, namely "int", "bool", "string", "path", "null", "set", "list", "lambda" or "float".
[5] It's parsed as an expression that selects the attribute sh from the variable builder.
[6] Actually, Nix detects infinite recursion in this case and aborts (“infinite recursion encountered”).
[7] To figure out your platform identifier, look at the line “Checking for the canonical Nix system name” in the output of Nix's configure script.
Nix supports remote builds, where a local Nix installation can forward Nix builds to other machines. This allows multiple builds to be performed in parallel and allows Nix to perform multi-platform builds in a semi-transparent way. For instance, if you perform a build for a x86_64-darwin on an i686-linux machine, Nix can automatically forward the build to a x86_64-darwin machine, if available.
To forward a build to a remote machine, it’s required that the remote machine is accessible via SSH and that it has Nix installed. You can test whether connecting to the remote Nix instance works, e.g.
$ nix ping-store --store ssh://mac
will try to connect to the machine named mac. It is possible to specify an SSH identity file as part of the remote store URI, e.g.
$ nix ping-store --store ssh://mac?ssh-key=/home/alice/my-key
Since builds should be non-interactive, the key should not have a passphrase. Alternatively, you can load identities ahead of time into ssh-agent or gpg-agent.
If you get the error
bash: nix-store: command not found error: cannot connect to 'mac'
then you need to ensure that the PATH of non-interactive login shells contains Nix.
root) that should have SSH access to the remote machine. If you can’t or don’t want to configure root to be able to access to remote machine, you can use a private Nix store instead by passing e.g. --store ~/my-nix.The list of remote machines can be specified on the command line or in the Nix configuration file. The former is convenient for testing. For example, the following command allows you to build a derivation for x86_64-darwin on a Linux machine:
$ uname
Linux
$ nix build \
'(with import <nixpkgs> { system = "x86_64-darwin"; }; runCommand "foo" {} "uname > $out")' \
--builders 'ssh://mac x86_64-darwin'
[1/0/1 built, 0.0 MiB DL] building foo on ssh://mac
$ cat ./result
Darwin
It is possible to specify multiple builders separated by a semicolon or a newline, e.g.
--builders 'ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd'
Each machine specification consists of the following elements, separated by spaces. Only the first element is required. To leave a field at its default, set it to -.
The URI of the remote store in the format ssh://[, e.g. username@]hostnamessh://nix@mac or ssh://mac. For backward compatibility, ssh:// may be omitted. The hostname may be an alias defined in your ~/.ssh/config.
A comma-separated list of Nix platform type identifiers, such as x86_64-darwin. It is possible for a machine to support multiple platform types, e.g., i686-linux,x86_64-linux. If omitted, this defaults to the local platform type.
The SSH identity file to be used to log in to the remote machine. If omitted, SSH will use its regular identities.
The maximum number of builds that Nix will execute in parallel on the machine. Typically this should be equal to the number of CPU cores. For instance, the machine itchy in the example will execute up to 8 builds in parallel.
The “speed factor”, indicating the relative speed of the machine. If there are multiple machines of the right type, Nix will prefer the fastest, taking load into account.
A comma-separated list of supported features. If a derivation has the requiredSystemFeatures attribute, then Nix will only perform the derivation on a machine that has the specified features. For instance, the attribute
requiredSystemFeatures = [ "kvm" ];
will cause the build to be performed on a machine that has the kvm feature.
A comma-separated list of mandatory features. A machine will only be used to build a derivation if all of the machine’s mandatory features appear in the derivation’s requiredSystemFeatures attribute..
For example, the machine specification
nix@scratchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 1 kvm nix@itchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 2 nix@poochie.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 1 2 kvm benchmark
specifies several machines that can perform i686-linux builds. However, poochie will only do builds that have the attribute
requiredSystemFeatures = [ "benchmark" ];
or
requiredSystemFeatures = [ "benchmark" "kvm" ];
itchy cannot do builds that require kvm, but scratchy does support such builds. For regular builds, itchy will be preferred over scratchy because it has a higher speed factor.
Remote builders can also be configured in nix.conf, e.g.
builders = ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd
Finally, remote builders can be configured in a separate configuration file included in builders via the syntax @. For example, file
builders = @/etc/nix/machines
causes the list of machines in /etc/nix/machines to be included. (This is the default.)
This section lists commands and options that you can use when you work with Nix.
Most Nix commands accept the following command-line options:
--helpPrints out a summary of the command syntax and exits.
--versionPrints out the Nix version number on standard output and exits.
--verbose / -vIncreases the level of verbosity of diagnostic messages printed on standard error. For each Nix operation, the information printed on standard output is well-defined; any diagnostic information is printed on standard error, never on standard output.
This option may be specified repeatedly. Currently, the following verbosity levels exist:
“Errors only”: only print messages explaining why the Nix invocation failed.
“Informational”: print useful messages about what Nix is doing. This is the default.
“Talkative”: print more informational messages.
“Chatty”: print even more informational messages.
“Debug”: print debug information.
“Vomit”: print vast amounts of debug information.
--quietDecreases the level of verbosity of diagnostic messages printed on standard error. This is the inverse option to -v / --verbose.
This option may be specified repeatedly. See the previous verbosity levels list.
--no-build-output / -QBy default, output written by builders to standard output and standard error is echoed to the Nix command's standard error. This option suppresses this behaviour. Note that the builder's standard output and error are always written to a log file in prefix/nix/var/log/nix
--max-jobs / -j numberSets the maximum number of build jobs that Nix will perform in parallel to the specified number. Specify auto to use the number of CPUs in the system. The default is specified by the max-jobs configuration setting, which itself defaults to 1. A higher value is useful on SMP systems or to exploit I/O latency.
--coresSets the value of the NIX_BUILD_CORES environment variable in the invocation of builders. Builders can use this variable at their discretion to control the maximum amount of parallelism. For instance, in Nixpkgs, if the derivation attribute enableParallelBuilding is set to true, the builder passes the -j flag to GNU Make. It defaults to the value of the Ncores configuration setting, if set, or 1 otherwise. The value 0 means that the builder should use all available CPU cores in the system.
--max-silent-timeSets the maximum number of seconds that a builder can go without producing any data on standard output or standard error. The default is specified by the max-silent-time configuration setting. 0 means no time-out.
--timeoutSets the maximum number of seconds that a builder can run. The default is specified by the timeout configuration setting. 0 means no timeout.
--keep-going / -kKeep going in case of failed builds, to the greatest extent possible. That is, if building an input of some derivation fails, Nix will still build the other inputs, but not the derivation itself. Without this option, Nix stops if any build fails (except for builds of substitutes), possibly killing builds in progress (in case of parallel or distributed builds).
--keep-failed / -KSpecifies that in case of a build failure, the temporary directory (usually in /tmp) in which the build takes place should not be deleted. The path of the build directory is printed as an informational message.
--fallbackWhenever Nix attempts to build a derivation for which substitutes are known for each output path, but realising the output paths through the substitutes fails, fall back on building the derivation.
The most common scenario in which this is useful is when we have registered substitutes in order to perform binary distribution from, say, a network repository. If the repository is down, the realisation of the derivation will fail. When this option is specified, Nix will build the derivation instead. Thus, installation from binaries falls back on installation from source. This option is not the default since it is generally not desirable for a transient failure in obtaining the substitutes to lead to a full build from source (with the related consumption of resources).
--no-build-hookDisables the build hook mechanism. This allows to ignore remote builders if they are setup on the machine.
It's useful in cases where the bandwidth between the client and the remote builder is too low. In that case it can take more time to upload the sources to the remote builder and fetch back the result than to do the computation locally.
--readonly-modeWhen this option is used, no attempt is made to open the Nix database. Most Nix operations do need database access, so those operations will fail.
--arg name valueThis option is accepted by nix-env, nix-instantiate and nix-build. When evaluating Nix expressions, the expression evaluator will automatically try to call functions that it encounters. It can automatically call functions for which every argument has a default value (e.g., { ). With argName ? defaultValue }: ...--arg, you can also call functions that have arguments without a default value (or override a default value). That is, if the evaluator encounters a function with an argument named name, it will call it with value value.
For instance, the top-level default.nix in Nixpkgs is actually a function:
{ # The system (e.g., `i686-linux') for which to build the packages.
system ? builtins.currentSystem
...
}: ... So if you call this Nix expression (e.g., when you do nix-env -i ), the function will be called automatically using the value pkgnamebuiltins.currentSystem for the system argument. You can override this using --arg, e.g., nix-env -i . (Note that since the argument is a Nix string literal, you have to escape the quotes.)pkgname --arg system \"i686-freebsd\"
--argstr name valueThis option is like --arg, only the value is not a Nix expression but a string. So instead of --arg system \"i686-linux\" (the outer quotes are to keep the shell happy) you can say --argstr system i686-linux.
--attr / -A attrPathSelect an attribute from the top-level Nix expression being evaluated. (nix-env, nix-instantiate, nix-build and nix-shell only.) The attribute path attrPath is a sequence of attribute names separated by dots. For instance, given a top-level Nix expression e, the attribute path xorg.xorgserver would cause the expression e.xorg.xorgserver
In addition to attribute names, you can also specify array indices. For instance, the attribute path foo.3.bar selects the bar attribute of the fourth element of the array in the foo attribute of the top-level expression.
--expr / -EInterpret the command line arguments as a list of Nix expressions to be parsed and evaluated, rather than as a list of file names of Nix expressions. (nix-instantiate, nix-build and nix-shell only.)
-I pathAdd a path to the Nix expression search path. This option may be given multiple times. See the NIX_PATH environment variable for information on the semantics of the Nix search path. Paths added through -I take precedence over NIX_PATH.
--option name valueSet the Nix configuration option name to value. This overrides settings in the Nix configuration file (see nix.conf(5)).
--repairFix corrupted or missing store paths by redownloading or rebuilding them. Note that this is slow because it requires computing a cryptographic hash of the contents of every path in the closure of the build. Also note the warning under nix-store --repair-path.
Most Nix commands interpret the following environment variables:
IN_NIX_SHELLIndicator that tells if the current environment was set up by nix-shell.
NIX_PATHA colon-separated list of directories used to look up Nix expressions enclosed in angle brackets (i.e., <). For instance, the value path>
/home/eelco/Dev:/etc/nixos
will cause Nix to look for paths relative to /home/eelco/Dev and /etc/nixos, in that order. It is also possible to match paths against a prefix. For example, the value
nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos
will cause Nix to search for <nixpkgs/ in path>/home/eelco/Dev/nixpkgs-branch/ and path/etc/nixos/nixpkgs/.path
If a path in the Nix search path starts with http:// or https://, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must consist of a single top-level directory. For example, setting NIX_PATH to
nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz
tells Nix to download the latest revision in the Nixpkgs/NixOS 14.12 channel.
The search path can be extended using the -I option, which takes precedence over NIX_PATH.
NIX_IGNORE_SYMLINK_STORENormally, the Nix store directory (typically /nix/store) is not allowed to contain any symlink components. This is to prevent “impure” builds. Builders sometimes “canonicalise” paths by resolving all symlink components. Thus, builds on different machines (with /nix/store resolving to different locations) could yield different results. This is generally not a problem, except when builds are deployed to machines where /nix/store resolves differently. If you are sure that you’re not going to do that, you can set NIX_IGNORE_SYMLINK_STORE to 1.
Note that if you’re symlinking the Nix store so that you can put it on another file system than the root file system, on Linux you’re better off using bind mount points, e.g.,
$ mkdir /nix $ mount -o bind /mnt/otherdisk/nix /nix
Consult the mount(8) manual page for details.
NIX_STORE_DIROverrides the location of the Nix store (default prefix/store
NIX_DATA_DIROverrides the location of the Nix static data directory (default prefix/share
NIX_LOG_DIROverrides the location of the Nix log directory (default prefix/log/nix
NIX_STATE_DIROverrides the location of the Nix state directory (default prefix/var/nix
NIX_CONF_DIROverrides the location of the Nix configuration directory (default prefix/etc/nix
TMPDIRUse the specified directory to store temporary files. In particular, this includes temporary build directories; these can take up substantial amounts of disk space. The default is /tmp.
NIX_REMOTEThis variable should be set to daemon if you want to use the Nix daemon to execute Nix operations. This is necessary in multi-user Nix installations. If the Nix daemon's Unix socket is at some non-standard path, this variable should be set to unix://path/to/socket. Otherwise, it should be left unset.
NIX_SHOW_STATSIf set to 1, Nix will print some evaluation statistics, such as the number of values allocated.
NIX_COUNT_CALLSIf set to 1, Nix will print how often functions were called during Nix expression evaluation. This is useful for profiling your Nix expressions.
GC_INITIAL_HEAP_SIZEIf Nix has been configured to use the Boehm garbage collector, this variable sets the initial size of the heap in bytes. It defaults to 384 MiB. Setting it to a low value reduces memory consumption, but will increase runtime due to the overhead of garbage collection.
This section lists commands and options that you can use when you work with Nix.
nix-env [--help] [--version] [ { --verbose | -v } ...] [ --quiet ] [ --no-build-output | -Q ] [ { --max-jobs | -j } number ] [ --cores number ] [ --max-silent-time number ] [ --timeout number ] [ --keep-going | -k ] [ --keep-failed | -K ] [--fallback] [--readonly-mode] [ -I path ] [ --option name value ]
[--arg name value] [--argstr name value] [ { --file | -f } path ] [ { --profile | -p } path ] [ --system-filter system ] [--dry-run] operation [options...] [arguments...]
The command nix-env is used to manipulate Nix user environments. User environments are sets of software packages available to a user at some point in time. In other words, they are a synthesised view of the programs available in the Nix store. There may be many user environments: different users can have different environments, and individual users can switch between different environments.
nix-env takes exactly one operation flag which indicates the subcommand to be performed. These are documented below.
Several commands, such as nix-env -q and nix-env -i, take a list of arguments that specify the packages on which to operate. These are extended regular expressions that must match the entire name of the package. (For details on regular expressions, see regex(7).) The match is case-sensitive. The regular expression can optionally be followed by a dash and a version number; if omitted, any version of the package will match. Here are some examples:
firefoxMatches the package name firefox and any version.
firefox-32.0Matches the package name firefox and version 32.0.
gtk\\+Matches the package name gtk+. The + character must be escaped using a backslash to prevent it from being interpreted as a quantifier, and the backslash must be escaped in turn with another backslash to ensure that the shell passes it on.
.\*Matches any package name. This is the default for most commands.
'.*zip.*'Matches any package name containing the string zip. Note the dots: '*zip*' does not work, because in a regular expression, the character * is interpreted as a quantifier.
'.*(firefox|chromium).*'Matches any package name containing the strings firefox or chromium.
This section lists the options that are common to all operations. These options are allowed for every subcommand, though they may not always have an effect. See also Chapter 17, Common Options.
--file / -f pathSpecifies the Nix expression (designated below as the active Nix expression) used by the --install, --upgrade, and --query --available operations to obtain derivations. The default is ~/.nix-defexpr.
If the argument starts with http:// or https://, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must include a single top-level directory containing at least a file named default.nix.
--profile / -p pathSpecifies the profile to be used by those operations that operate on a profile (designated below as the active profile). A profile is a sequence of user environments called generations, one of which is the current generation.
--dry-runFor the --install, --upgrade, --uninstall, --switch-generation, --delete-generations and --rollback operations, this flag will cause nix-env to print what would be done if this flag had not been specified, without actually doing it.
--dry-run also prints out which paths will be substituted (i.e., downloaded) and which paths will be built from source (because no substitute is available).
--system-filter systemBy default, operations such as --query --available show derivations matching any platform. This option allows you to use derivations for the specified platform system.
~/.nix-defexprA directory that contains the default Nix expressions used by the --install, --upgrade, and --query --available operations to obtain derivations. The --file option may be used to override this default.
The Nix expressions in this directory are combined into a single set, with each file as an attribute that has the name of the file. Thus, if ~/.nix-defexpr contains two files, foo and bar, then the default Nix expression will essentially be
{
foo = import ~/.nix-defexpr/foo;
bar = import ~/.nix-defexpr/bar;
}
The command nix-channel places symlinks to the downloaded Nix expressions from each subscribed channel in this directory.
~/.nix-profileA symbolic link to the user's current profile. By default, this symlink points to prefix/var/nix/profiles/defaultPATH environment variable should include ~/.nix-profile/bin for the user environment to be visible to the user.
--installnix-env { --install | -i } [ { --prebuilt-only | -b } ] [ { --attr | -A } ] [--from-expression] [-E] [--from-profile path] [ --preserve-installed | -P ] [ --remove-all | -r ] args...
The install operation creates a new user environment, based on the current generation of the active profile, to which a set of store paths described by args is added. The arguments args map to store paths in a number of possible ways:
By default, args is a set of derivation names denoting derivations in the active Nix expression. These are realised, and the resulting output paths are installed. Currently installed derivations with a name equal to the name of a derivation being added are removed unless the option --preserve-installed is specified.
If there are multiple derivations matching a name in args that have the same name (e.g., gcc-3.3.6 and gcc-4.1.1), then the derivation with the highest priority is used. A derivation can define a priority by declaring the meta.priority attribute. This attribute should be a number, with a higher value denoting a lower priority. The default priority is 0.
If there are multiple matching derivations with the same priority, then the derivation with the highest version will be installed.
You can force the installation of multiple derivations with the same name by being specific about the versions. For instance, nix-env -i gcc-3.3.6 gcc-4.1.1 will install both version of GCC (and will probably cause a user environment conflict!).
If --attr (-A) is specified, the arguments are attribute paths that select attributes from the top-level Nix expression. This is faster than using derivation names and unambiguous. To find out the attribute paths of available packages, use nix-env -qaP.
If --from-profile path is given, args is a set of names denoting installed store paths in the profile path. This is an easy way to copy user environment elements from one profile to another.
If --from-expression is given, args are Nix functions that are called with the active Nix expression as their single argument. The derivations returned by those function calls are installed. This allows derivations to be specified in an unambiguous way, which is necessary if there are multiple derivations with the same name.
If args are store derivations, then these are realised, and the resulting output paths are installed.
If args are store paths that are not store derivations, then these are realised and installed.
By default all outputs are installed for each derivation. That can be reduced by setting meta.outputsToInstall.
--prebuilt-only / -bUse only derivations for which a substitute is registered, i.e., there is a pre-built binary available that can be downloaded in lieu of building the derivation. Thus, no packages will be built from source.
--preserve-installed, -PDo not remove derivations with a name matching one of the derivations being installed. Usually, trying to have two versions of the same package installed in the same generation of a profile will lead to an error in building the generation, due to file name clashes between the two versions. However, this is not the case for all packages.
--remove-all, -rRemove all previously installed packages first. This is equivalent to running nix-env -e '.*' first, except that everything happens in a single transaction.
To install a specific version of gcc from the active Nix expression:
$ nix-env --install gcc-3.3.2 installing `gcc-3.3.2' uninstalling `gcc-3.1'
Note the previously installed version is removed, since --preserve-installed was not specified.
To install an arbitrary version:
$ nix-env --install gcc installing `gcc-3.3.2'
To install using a specific attribute:
$ nix-env -i -A gcc40mips $ nix-env -i -A xorg.xorgserver
To install all derivations in the Nix expression foo.nix:
$ nix-env -f ~/foo.nix -i '.*'
To copy the store path with symbolic name gcc from another profile:
$ nix-env -i --from-profile /nix/var/nix/profiles/foo gcc
To install a specific store derivation (typically created by nix-instantiate):
$ nix-env -i /nix/store/fibjb1bfbpm5mrsxc4mh2d8n37sxh91i-gcc-3.4.3.drv
To install a specific output path:
$ nix-env -i /nix/store/y3cgx0xj1p4iv9x0pnnmdhr8iyg741vk-gcc-3.4.3
To install from a Nix expression specified on the command-line:
$ nix-env -f ./foo.nix -i -E \
'f: (f {system = "i686-linux";}).subversionWithJava' I.e., this evaluates to (f: (f {system = "i686-linux";}).subversionWithJava) (import ./foo.nix), thus selecting the subversionWithJava attribute from the set returned by calling the function defined in ./foo.nix.
A dry-run tells you which paths will be downloaded or built from source:
$ nix-env -f '<nixpkgs>' -iA hello --dry-run
(dry run; not doing anything)
installing ‘hello-2.10’
these paths will be fetched (0.04 MiB download, 0.19 MiB unpacked):
/nix/store/wkhdf9jinag5750mqlax6z2zbwhqb76n-hello-2.10
...
To install Firefox from the latest revision in the Nixpkgs/NixOS 14.12 channel:
$ nix-env -f https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz -iA firefox
(The GitHub repository nixpkgs-channels is updated automatically from the main nixpkgs repository after certain tests have succeeded and binaries have been built and uploaded to the binary cache at cache.nixos.org.)
--upgradenix-env { --upgrade | -u } [ { --prebuilt-only | -b } ] [ { --attr | -A } ] [--from-expression] [-E] [--from-profile path] [ --lt | --leq | --eq | --always ] args...
The upgrade operation creates a new user environment, based on the current generation of the active profile, in which all store paths are replaced for which there are newer versions in the set of paths described by args. Paths for which there are no newer versions are left untouched; this is not an error. It is also not an error if an element of args matches no installed derivations.
For a description of how args is mapped to a set of store paths, see --install. If args describes multiple store paths with the same symbolic name, only the one with the highest version is installed.
--ltOnly upgrade a derivation to newer versions. This is the default.
--leqIn addition to upgrading to newer versions, also “upgrade” to derivations that have the same version. Version are not a unique identification of a derivation, so there may be many derivations that have the same version. This flag may be useful to force “synchronisation” between the installed and available derivations.
--eqOnly “upgrade” to derivations that have the same version. This may not seem very useful, but it actually is, e.g., when there is a new release of Nixpkgs and you want to replace installed applications with the same versions built against newer dependencies (to reduce the number of dependencies floating around on your system).
--alwaysIn addition to upgrading to newer versions, also “upgrade” to derivations that have the same or a lower version. I.e., derivations may actually be downgraded depending on what is available in the active Nix expression.
For the other flags, see --install.
$ nix-env --upgrade gcc upgrading `gcc-3.3.1' to `gcc-3.4' $ nix-env -u gcc-3.3.2 --always (switch to a specific version) upgrading `gcc-3.4' to `gcc-3.3.2' $ nix-env --upgrade pan (no upgrades available, so nothing happens) $ nix-env -u (try to upgrade everything) upgrading `hello-2.1.2' to `hello-2.1.3' upgrading `mozilla-1.2' to `mozilla-1.4'
The upgrade operation determines whether a derivation y is an upgrade of a derivation x by looking at their respective name attributes. The names (e.g., gcc-3.3.1 are split into two parts: the package name (gcc), and the version (3.3.1). The version part starts after the first dash not following by a letter. x is considered an upgrade of y if their package names match, and the version of y is higher that that of x.
The versions are compared by splitting them into contiguous components of numbers and letters. E.g., 3.3.1pre5 is split into [3, 3, 1, "pre", 5]. These lists are then compared lexicographically (from left to right). Corresponding components a and b are compared as follows. If they are both numbers, integer comparison is used. If a is an empty string and b is a number, a is considered less than b. The special string component pre (for pre-release) is considered to be less than other components. String components are considered less than number components. Otherwise, they are compared lexicographically (i.e., using case-sensitive string comparison).
This is illustrated by the following examples:
1.0 < 2.3 2.1 < 2.3 2.3 = 2.3 2.5 > 2.3 3.1 > 2.3 2.3.1 > 2.3 2.3.1 > 2.3a 2.3pre1 < 2.3 2.3pre3 < 2.3pre12 2.3a < 2.3c 2.3pre1 < 2.3c 2.3pre1 < 2.3q
--uninstall--set--set-flagThe --set-flag operation allows meta attributes of installed packages to be modified. There are several attributes that can be usefully modified, because they affect the behaviour of nix-env or the user environment build script:
priority can be changed to resolve filename clashes. The user environment build script uses the meta.priority attribute of derivations to resolve filename collisions between packages. Lower priority values denote a higher priority. For instance, the GCC wrapper package and the Binutils package in Nixpkgs both have a file bin/ld, so previously if you tried to install both you would get a collision. Now, on the other hand, the GCC wrapper declares a higher priority than Binutils, so the former’s bin/ld is symlinked in the user environment.
keep can be set to true to prevent the package from being upgraded or replaced. This is useful if you want to hang on to an older version of a package.
active can be set to false to “disable” the package. That is, no symlinks will be generated to the files of the package, but it remains part of the profile (so it won’t be garbage-collected). It can be set back to true to re-enable the package.
To prevent the currently installed Firefox from being upgraded:
$ nix-env --set-flag keep true firefox
After this, nix-env -u will ignore Firefox.
To disable the currently installed Firefox, then install a new Firefox while the old remains part of the profile:
$ nix-env -q firefox-2.0.0.9 (the current one) $ nix-env --preserve-installed -i firefox-2.0.0.11 installing `firefox-2.0.0.11' building path(s) `/nix/store/myy0y59q3ig70dgq37jqwg1j0rsapzsl-user-environment' collision between `/nix/store/...-firefox-2.0.0.11/bin/firefox' and `/nix/store/...-firefox-2.0.0.9/bin/firefox'. (i.e., can’t have two active at the same time) $ nix-env --set-flag active false firefox setting flag on `firefox-2.0.0.9' $ nix-env --preserve-installed -i firefox-2.0.0.11 installing `firefox-2.0.0.11' $ nix-env -q firefox-2.0.0.11 (the enabled one) firefox-2.0.0.9 (the disabled one)
To make files from binutils take precedence over files from gcc:
$ nix-env --set-flag priority 5 binutils $ nix-env --set-flag priority 10 gcc
--querynix-env { --query | -q } [ --installed | --available | -a ]
[ { --status | -s } ] [ { --attr-path | -P } ] [--no-name] [ { --compare-versions | -c } ] [--system] [--drv-path] [--out-path] [--description] [--meta]
[--xml] [--json] [ { --prebuilt-only | -b } ] [ { --attr | -A } attribute-path ]
names...
The query operation displays information about either the store paths that are installed in the current generation of the active profile (--installed), or the derivations that are available for installation in the active Nix expression (--available). It only prints information about derivations whose symbolic name matches one of names.
The derivations are sorted by their name attributes.
The following flags specify the set of things on which the query operates.
--installedThe query operates on the store paths that are installed in the current generation of the active profile. This is the default.
--available, -aThe query operates on the derivations that are available in the active Nix expression.
The following flags specify what information to display about the selected derivations. Multiple flags may be specified, in which case the information is shown in the order given here. Note that the name of the derivation is shown unless --no-name is specified.
--xmlPrint the result in an XML representation suitable for automatic processing by other tools. The root element is called items, which contains a item element for each available or installed derivation. The fields discussed below are all stored in attributes of the item elements.
--jsonPrint the result in a JSON representation suitable for automatic processing by other tools.
--prebuilt-only / -bShow only derivations for which a substitute is registered, i.e., there is a pre-built binary available that can be downloaded in lieu of building the derivation. Thus, this shows all packages that probably can be installed quickly.
--status, -sPrint the status of the derivation. The status consists of three characters. The first is I or -, indicating whether the derivation is currently installed in the current generation of the active profile. This is by definition the case for --installed, but not for --available. The second is P or -, indicating whether the derivation is present on the system. This indicates whether installation of an available derivation will require the derivation to be built. The third is S or -, indicating whether a substitute is available for the derivation.
--attr-path, -PPrint the attribute path of the derivation, which can be used to unambiguously select it using the --attr option available in commands that install derivations like nix-env --install.
--no-nameSuppress printing of the name attribute of each derivation.
--compare-versions / -cCompare installed versions to available versions, or vice versa (if --available is given). This is useful for quickly seeing whether upgrades for installed packages are available in a Nix expression. A column is added with the following meaning:
< versionA newer version of the package is available or installed.
= versionAt most the same version of the package is available or installed.
> versionOnly older versions of the package are available or installed.
- ?No version of the package is available or installed.
--systemPrint the system attribute of the derivation.
--drv-pathPrint the path of the store derivation.
--out-pathPrint the output path of the derivation.
--descriptionPrint a short (one-line) description of the derivation, if available. The description is taken from the meta.description attribute of the derivation.
--metaPrint all of the meta-attributes of the derivation. This option is only available with --xml or --json.
To show installed packages:
$ nix-env -q
bison-1.875c
docbook-xml-4.2
firefox-1.0.4
MPlayer-1.0pre7
ORBit2-2.8.3
…
To show available packages:
$ nix-env -qa
firefox-1.0.7
GConf-2.4.0.1
MPlayer-1.0pre7
ORBit2-2.8.3
…
To show the status of available packages:
$ nix-env -qas
-P- firefox-1.0.7 (not installed but present)
--S GConf-2.4.0.1 (not present, but there is a substitute for fast installation)
--S MPlayer-1.0pre3 (i.e., this is not the installed MPlayer, even though the version is the same!)
IP- ORBit2-2.8.3 (installed and by definition present)
…
To show available packages in the Nix expression foo.nix:
$ nix-env -f ./foo.nix -qa foo-1.2.3
To compare installed versions to what’s available:
$ nix-env -qc...acrobat-reader-7.0 - ? (package is not available at all) autoconf-2.59 = 2.59 (same version) firefox-1.0.4 < 1.0.7 (a more recent version is available)...
To show all packages with “zip” in the name:
$ nix-env -qa '.*zip.*'
bzip2-1.0.6
gzip-1.6
zip-3.0
…
To show all packages with “firefox” or “chromium” in the name:
$ nix-env -qa '.*(firefox|chromium).*'
chromium-37.0.2062.94
chromium-beta-38.0.2125.24
firefox-32.0.3
firefox-with-plugins-13.0.1
…
To show all packages in the latest revision of the Nixpkgs repository:
$ nix-env -f https://github.com/NixOS/nixpkgs/archive/master.tar.gz -qa
--switch-profile--list-generations--delete-generationsThis operation deletes the specified generations of the current profile. The generations can be a list of generation numbers, the special value old to delete all non-current generations, a value such as 30d to delete all generations older than the specified number of days (except for the generation that was active at that point in time), or a value such as. +5 to only keep the specified items older than the current generation. Periodically deleting old generations is important to make garbage collection effective.
--switch-generationThis operation makes generation number generation the current generation of the active profile. That is, if the profileprofileprofile-generation-link
Switching will fail if the specified generation does not exist.
nix-build [--help] [--version] [ { --verbose | -v } ...] [ --quiet ] [ --no-build-output | -Q ] [ { --max-jobs | -j } number ] [ --cores number ] [ --max-silent-time number ] [ --timeout number ] [ --keep-going | -k ] [ --keep-failed | -K ] [--fallback] [--readonly-mode] [ -I path ] [ --option name value ]
[--arg name value] [--argstr name value] [ { --attr | -A } attrPath ] [--no-out-link] [ { --out-link | -o } outlink ] paths...
The nix-build command builds the derivations described by the Nix expressions in paths. If the build succeeds, it places a symlink to the result in the current directory. The symlink is called result. If there are multiple Nix expressions, or the Nix expressions evaluate to multiple derivations, multiple sequentially numbered symlinks are created (result, result-2, and so on).
If no paths are specified, then nix-build will use default.nix in the current directory, if it exists.
If an element of paths starts with http:// or https://, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must include a single top-level directory containing at least a file named default.nix.
nix-build is essentially a wrapper around nix-instantiate (to translate a high-level Nix expression to a low-level store derivation) and nix-store --realise (to build the store derivation).
result symlink is deleted or renamed. So don’t rename the symlink.All options not listed here are passed to nix-store --realise, except for --arg and --attr / -A which are passed to nix-instantiate. See also Chapter 17, Common Options.
The following common options are supported:
$ nix-build '<nixpkgs>' -A firefox
store derivation is /nix/store/qybprl8sz2lc...-firefox-1.5.0.7.drv
/nix/store/d18hyl92g30l...-firefox-1.5.0.7
$ ls -l result
lrwxrwxrwx ... result -> /nix/store/d18hyl92g30l...-firefox-1.5.0.7
$ ls ./result/bin/
firefox firefox-configIf a derivation has multiple outputs, nix-build will build the default (first) output. You can also build all outputs:
$ nix-build '<nixpkgs>' -A openssl.all
This will create a symlink for each output named result-. The suffix is omitted if the output name is outputnameout. So if openssl has outputs out, bin and man, nix-build will create symlinks result, result-bin and result-man. It’s also possible to build a specific output:
$ nix-build '<nixpkgs>' -A openssl.man
This will create a symlink result-man.
Build a Nix expression given on the command line:
$ nix-build -E 'with import <nixpkgs> { }; runCommand "foo" { } "echo bar > $out"'
$ cat ./result
bar
Build the GNU Hello package from the latest revision of the master branch of Nixpkgs:
$ nix-build https://github.com/NixOS/nixpkgs/archive/master.tar.gz -A hello
nix-shell [--arg name value] [--argstr name value] [ { --attr | -A } attrPath ] [--command cmd] [--run cmd] [--exclude regexp] [--pure] [--keep name] { { --packages | -p } packages... | [path]}
The command nix-shell will build the dependencies of the specified derivation, but not the derivation itself. It will then start an interactive shell in which all environment variables defined by the derivation path have been set to their corresponding values, and the script $stdenv/setup has been sourced. This is useful for reproducing the environment of a derivation for development.
If path is not given, nix-shell defaults to shell.nix if it exists, and default.nix otherwise.
If path starts with http:// or https://, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must include a single top-level directory containing at least a file named default.nix.
If the derivation defines the variable shellHook, it will be evaluated after $stdenv/setup has been sourced. Since this hook is not executed by regular Nix builds, it allows you to perform initialisation specific to nix-shell. For example, the derivation attribute
shellHook =
''
echo "Hello shell"
'';
will cause nix-shell to print Hello shell.
All options not listed here are passed to nix-store --realise, except for --arg and --attr / -A which are passed to nix-instantiate. See also Chapter 17, Common Options.
--command cmdIn the environment of the derivation, run the shell command cmd. This command is executed in an interactive shell. (Use --run to use a non-interactive shell instead.) However, a call to exit is implicitly added to the command, so the shell will exit after running the command. To prevent this, add return at the end; e.g. --command "echo Hello; return" will print Hello and then drop you into the interactive shell. This can be useful for doing any additional initialisation.
--run cmdLike --command, but executes the command in a non-interactive shell. This means (among other things) that if you hit Ctrl-C while the command is running, the shell exits.
--exclude regexpDo not build any dependencies whose store path matches the regular expression regexp. This option may be specified multiple times.
--pureIf this flag is specified, the environment is almost entirely cleared before the interactive shell is started, so you get an environment that more closely corresponds to the “real” Nix build. A few variables, in particular HOME, USER and DISPLAY, are retained. Note that ~/.bashrc and (depending on your Bash installation) /etc/bashrc are still sourced, so any variables set there will affect the interactive shell.
--packages / -p packages…Set up an environment in which the specified packages are present. The command line arguments are interpreted as attribute names inside the Nix Packages collection. Thus, nix-shell -p libjpeg openjdk will start a shell in which the packages denoted by the attribute names libjpeg and openjdk are present.
-i interpreterThe chained script interpreter to be invoked by nix-shell. Only applicable in #!-scripts (described below).
--keep nameWhen a --pure shell is started, keep the listed environment variables.
The following common options are supported:
NIX_BUILD_SHELLShell used to start the interactive environment. Defaults to the bash found in PATH.
To build the dependencies of the package Pan, and start an interactive shell in which to build it:
$ nix-shell '<nixpkgs>' -A pan [nix-shell]$ unpackPhase [nix-shell]$ cd pan-* [nix-shell]$ configurePhase [nix-shell]$ buildPhase [nix-shell]$ ./pan/gui/pan
To clear the environment first, and do some additional automatic initialisation of the interactive shell:
$ nix-shell '<nixpkgs>' -A pan --pure \
--command 'export NIX_DEBUG=1; export NIX_CORES=8; return'
Nix expressions can also be given on the command line. For instance, the following starts a shell containing the packages sqlite and libX11:
$ nix-shell -E 'with import <nixpkgs> { }; runCommand "dummy" { buildInputs = [ sqlite xorg.libX11 ]; } ""'
A shorter way to do the same is:
$ nix-shell -p sqlite xorg.libX11 [nix-shell]$ echo $NIX_LDFLAGS … -L/nix/store/j1zg5v…-sqlite-3.8.0.2/lib -L/nix/store/0gmcz9…-libX11-1.6.1/lib …
The -p flag looks up Nixpkgs in the Nix search path. You can override it by passing -I or setting NIX_PATH. For example, the following gives you a shell containing the Pan package from a specific revision of Nixpkgs:
$ nix-shell -p pan -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/8a3eea054838b55aca962c3fbde9c83c102b8bf2.tar.gz [nix-shell:~]$ pan --version Pan 0.139
#!-interpreterYou can use nix-shell as a script interpreter to allow scripts written in arbitrary languages to obtain their own dependencies via Nix. This is done by starting the script with the following lines:
#! /usr/bin/env nix-shell #! nix-shell -ireal-interpreter-ppackages
where real-interpreter is the “real” script interpreter that will be invoked by nix-shell after it has obtained the dependencies and initialised the environment, and packages are the attribute names of the dependencies in Nixpkgs.
The lines starting with #! nix-shell specify nix-shell options (see above). Note that you cannot write #! /usr/bin/env nix-shell -i ... because many operating systems only allow one argument in #! lines.
For example, here is a Python script that depends on Python and the prettytable package:
#! /usr/bin/env nix-shell #! nix-shell -i python -p python pythonPackages.prettytable import prettytable # Print a simple table. t = prettytable.PrettyTable(["N", "N^2"]) for n in range(1, 10): t.add_row([n, n * n]) print t
Similarly, the following is a Perl script that specifies that it requires Perl and the HTML::TokeParser::Simple and LWP packages:
#! /usr/bin/env nix-shell
#! nix-shell -i perl -p perl perlPackages.HTMLTokeParserSimple perlPackages.LWP
use HTML::TokeParser::Simple;
# Fetch nixos.org and print all hrefs.
my $p = HTML::TokeParser::Simple->new(url => 'http://nixos.org/');
while (my $token = $p->get_tag("a")) {
my $href = $token->get_attr("href");
print "$href\n" if $href;
}
Sometimes you need to pass a simple Nix expression to customize a package like Terraform:
#! /usr/bin/env nix-shell #! nix-shell -i bash -p "terraform.withPlugins (plugins: [ plugins.openstack ])" terraform apply
") when passing a simple Nix expression in a nix-shell shebang.
Finally, using the merging of multiple nix-shell shebangs the following Haskell script uses a specific branch of Nixpkgs/NixOS (the 18.03 stable branch):
#! /usr/bin/env nix-shell #! nix-shell -i runghc -p haskellPackages.ghc haskellPackages.HTTP haskellPackages.tagsoup #! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.03.tar.gz import Network.HTTP import Text.HTML.TagSoup -- Fetch nixos.org and print all hrefs. main = do resp <- Network.HTTP.simpleHTTP (getRequest "http://nixos.org/") body <- getResponseBody resp let tags = filter (isTagOpenName "a") $ parseTags body let tags' = map (fromAttrib "href") tags mapM_ putStrLn $ filter (/= "") tags'
If you want to be even more precise, you can specify a specific revision of Nixpkgs:
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/0672315759b3e15e2121365f067c1c8c56bb4722.tar.gz
The examples above all used -p to get dependencies from Nixpkgs. You can also use a Nix expression to build your own dependencies. For example, the Python example could have been written as:
#! /usr/bin/env nix-shell #! nix-shell deps.nix -i python
where the file deps.nix in the same directory as the #!-script contains:
with import <nixpkgs> {};
runCommand "dummy" { buildInputs = [ python pythonPackages.prettytable ]; } ""
nix-store [--help] [--version] [ { --verbose | -v } ...] [ --quiet ] [ --no-build-output | -Q ] [ { --max-jobs | -j } number ] [ --cores number ] [ --max-silent-time number ] [ --timeout number ] [ --keep-going | -k ] [ --keep-failed | -K ] [--fallback] [--readonly-mode] [ -I path ] [ --option name value ]
[--add-root path] [--indirect] operation [options...] [arguments...]
The command nix-store performs primitive operations on the Nix store. You generally do not need to run this command manually.
nix-store takes exactly one operation flag which indicates the subcommand to be performed. These are documented below.
This section lists the options that are common to all operations. These options are allowed for every subcommand, though they may not always have an effect. See also Chapter 17, Common Options for a list of common options.
--add-root pathCauses the result of a realisation (--realise and --force-realise) to be registered as a root of the garbage collector (see Section 11.1, “Garbage Collector Roots”). The root is stored in path, which must be inside a directory that is scanned for roots by the garbage collector (i.e., typically in a subdirectory of /nix/var/nix/gcroots/) unless the --indirect flag is used.
If there are multiple results, then multiple symlinks will be created by sequentially numbering symlinks beyond the first one (e.g., foo, foo-2, foo-3, and so on).
--indirectIn conjunction with --add-root, this option allows roots to be stored outside of the GC roots directory. This is useful for commands such as nix-build that place a symlink to the build result in the current directory; such a build result should not be garbage-collected unless the symlink is removed.
The --indirect flag causes a uniquely named symlink to path to be stored in /nix/var/nix/gcroots/auto/. For instance,
$ nix-store --add-root /home/eelco/bla/result --indirect -r ...
$ ls -l /nix/var/nix/gcroots/auto
lrwxrwxrwx 1 ... 2005-03-13 21:10 dn54lcypm8f8... -> /home/eelco/bla/result
$ ls -l /home/eelco/bla/result
lrwxrwxrwx 1 ... 2005-03-13 21:10 /home/eelco/bla/result -> /nix/store/1r11343n6qd4...-f-spot-0.0.10 Thus, when /home/eelco/bla/result is removed, the GC root in the auto directory becomes a dangling symlink and will be ignored by the collector.
auto directory will still point to the old location.--realiseThe operation --realise essentially “builds” the specified store paths. Realisation is a somewhat overloaded term:
If the store path is a derivation, realisation ensures that the output paths of the derivation are valid (i.e., the output path and its closure exist in the file system). This can be done in several ways. First, it is possible that the outputs are already valid, in which case we are done immediately. Otherwise, there may be substitutes that produce the outputs (e.g., by downloading them). Finally, the outputs can be produced by performing the build action described by the derivation.
If the store path is not a derivation, realisation ensures that the specified path is valid (i.e., it and its closure exist in the file system). If the path is already valid, we are done immediately. Otherwise, the path and any missing paths in its closure may be produced through substitutes. If there are no (successful) subsitutes, realisation fails.
The output path of each derivation is printed on standard output. (For non-derivations argument, the argument itself is printed.)
The following flags are available:
--dry-runPrint on standard error a description of what packages would be built or downloaded, without actually performing the operation.
--ignore-unknownIf a non-derivation path does not have a substitute, then silently ignore it.
--checkThis option allows you to check whether a derivation is deterministic. It rebuilds the specified derivation and checks whether the result is bitwise-identical with the existing outputs, printing an error if that’s not the case. The outputs of the specified derivation must already exist. When used with -K, if an output path is not identical to the corresponding output from the previous build, the new output path is left in /nix/store/name.check.
See also the build-repeat configuration option, which repeats a derivation a number of times and prevents its outputs from being registered as “valid” in the Nix store unless they are identical.
This operation is typically used to build store derivations produced by nix-instantiate:
$ nix-store -r $(nix-instantiate ./test.nix) /nix/store/31axcgrlbfsxzmfff1gyj1bf62hvkby2-aterm-2.3.1
This is essentially what nix-build does.
To test whether a previously-built derivation is deterministic:
$ nix-build '<nixpkgs>' -A hello --check -K
--serveThe operation --serve provides access to the Nix store over stdin and stdout, and is intended to be used as a means of providing Nix store access to a restricted ssh user.
The following flags are available:
--writeAllow the connected client to request the realization of derivations. In effect, this can be used to make the host act as a build slave.
--gcnix-store --gc [ --print-roots | --print-live | --print-dead | --delete ] [--max-freed bytes]
Without additional flags, the operation --gc performs a garbage collection on the Nix store. That is, all paths in the Nix store not reachable via file system references from a set of “roots”, are deleted.
The following suboperations may be specified:
--print-rootsThis operation prints on standard output the set of roots used by the garbage collector. What constitutes a root is described in Section 11.1, “Garbage Collector Roots”.
--print-liveThis operation prints on standard output the set of “live” store paths, which are all the store paths reachable from the roots. Live paths should never be deleted, since that would break consistency — it would become possible that applications are installed that reference things that are no longer present in the store.
--print-deadThis operation prints out on standard output the set of “dead” store paths, which is just the opposite of the set of live paths: any path in the store that is not live (with respect to the roots) is dead.
--deleteThis operation performs an actual garbage collection. All dead paths are removed from the store. This is the default.
By default, all unreachable paths are deleted. The following options control what gets deleted and in what order:
--max-freed bytesKeep deleting paths until at least bytes bytes have been deleted, then stop. The argument bytes can be followed by the multiplicative suffix K, M, G or T, denoting KiB, MiB, GiB or TiB units.
The behaviour of the collector is also influenced by the keep-outputs and keep-derivations variables in the Nix configuration file.
With --delete, the collector prints the total number of freed bytes when it finishes (or when it is interrupted). With --print-dead, it prints the number of bytes that would be freed.
--deleteThe operation --delete deletes the store paths paths from the Nix store, but only if it is safe to do so; that is, when the path is not reachable from a root of the garbage collector. This means that you can only delete paths that would also be deleted by nix-store --gc. Thus, --delete is a more targeted version of --gc.
With the option --ignore-liveness, reachability from the roots is ignored. However, the path still won’t be deleted if there are other paths in the store that refer to it (i.e., depend on it).
--querynix-store { --query | -q } { --outputs | --requisites | -R | --references | --referrers | --referrers-closure | --deriver | -d | --graph | --tree | --binding name | -b name | --hash | --size | --roots } [--use-output] [-u] [--force-realise] [-f] paths...
The operation --query displays various bits of information about the store paths . The queries are described below. At most one query can be specified. The default query is --outputs.
The paths paths may also be symlinks from outside of the Nix store, to the Nix store. In that case, the query is applied to the target of the symlink.
--use-output, -uFor each argument to the query that is a store derivation, apply the query to the output path of the derivation instead.
--force-realise, -fRealise each argument to the query first (see nix-store --realise).
--outputsPrints out the output paths of the store derivations paths. These are the paths that will be produced when the derivation is built.
--requisites, -RPrints out the closure of the store path paths.
This query has one option:
--include-outputsAlso include the output path of store derivations, and their closures.
This query can be used to implement various kinds of deployment. A source deployment is obtained by distributing the closure of a store derivation. A binary deployment is obtained by distributing the closure of an output path. A cache deployment (combined source/binary deployment, including binaries of build-time-only dependencies) is obtained by distributing the closure of a store derivation and specifying the option --include-outputs.
--referencesPrints the set of references of the store paths paths, that is, their immediate dependencies. (For all dependencies, use --requisites.)
--referrersPrints the set of referrers of the store paths paths, that is, the store paths currently existing in the Nix store that refer to one of paths. Note that contrary to the references, the set of referrers is not constant; it can change as store paths are added or removed.
--referrers-closurePrints the closure of the set of store paths paths under the referrers relation; that is, all store paths that directly or indirectly refer to one of paths. These are all the path currently in the Nix store that are dependent on paths.
--deriver, -dPrints the deriver of the store paths paths. If the path has no deriver (e.g., if it is a source file), or if the deriver is not known (e.g., in the case of a binary-only deployment), the string unknown-deriver is printed.
--graphPrints the references graph of the store paths paths in the format of the dot tool of AT&T's Graphviz package. This can be used to visualise dependency graphs. To obtain a build-time dependency graph, apply this to a store derivation. To obtain a runtime dependency graph, apply it to an output path.
--treePrints the references graph of the store paths paths as a nested ASCII tree. References are ordered by descending closure size; this tends to flatten the tree, making it more readable. The query only recurses into a store path when it is first encountered; this prevents a blowup of the tree representation of the graph.
--binding name, -b namePrints the value of the attribute name (i.e., environment variable) of the store derivations paths. It is an error for a derivation to not have the specified attribute.
--hashPrints the SHA-256 hash of the contents of the store paths paths (that is, the hash of the output of nix-store --dump on the given paths). Since the hash is stored in the Nix database, this is a fast operation.
--sizePrints the size in bytes of the contents of the store paths paths — to be precise, the size of the output of nix-store --dump on the given paths. Note that the actual disk space required by the store paths may be higher, especially on filesystems with large cluster sizes.
--rootsPrints the garbage collector roots that point, directly or indirectly, at the store paths paths.
Print the closure (runtime dependencies) of the svn program in the current user environment:
$ nix-store -qR $(which svn)
/nix/store/5mbglq5ldqld8sj57273aljwkfvj22mc-subversion-1.1.4
/nix/store/9lz9yc6zgmc0vlqmn2ipcpkjlmbi51vv-glibc-2.3.4
...
Print the build-time dependencies of svn:
$ nix-store -qR $(nix-store -qd $(which svn))
/nix/store/02iizgn86m42q905rddvg4ja975bk2i4-grep-2.5.1.tar.bz2.drv
/nix/store/07a2bzxmzwz5hp58nf03pahrv2ygwgs3-gcc-wrapper.sh
/nix/store/0ma7c9wsbaxahwwl04gbw3fcd806ski4-glibc-2.3.4.drv
... lots of other paths ... The difference with the previous example is that we ask the closure of the derivation (-qd), not the closure of the output path that contains svn.
Show the build-time dependencies as a tree:
$ nix-store -q --tree $(nix-store -qd $(which svn))
/nix/store/7i5082kfb6yjbqdbiwdhhza0am2xvh6c-subversion-1.1.4.drv
+---/nix/store/d8afh10z72n8l1cr5w42366abiblgn54-builder.sh
+---/nix/store/fmzxmpjx2lh849ph0l36snfj9zdibw67-bash-3.0.drv
| +---/nix/store/570hmhmx3v57605cqg9yfvvyh0nnb8k8-bash
| +---/nix/store/p3srsbd8dx44v2pg6nbnszab5mcwx03v-builder.sh
...
Show all paths that depend on the same OpenSSL library as svn:
$ nix-store -q --referrers $(nix-store -q --binding openssl $(nix-store -qd $(which svn))) /nix/store/23ny9l9wixx21632y2wi4p585qhva1q8-sylpheed-1.0.0 /nix/store/5mbglq5ldqld8sj57273aljwkfvj22mc-subversion-1.1.4 /nix/store/dpmvp969yhdqs7lm2r1a3gng7pyq6vy4-subversion-1.1.3 /nix/store/l51240xqsgg8a7yrbqdx1rfzyv6l26fx-lynx-2.8.5
Show all paths that directly or indirectly depend on the Glibc (C library) used by svn:
$ nix-store -q --referrers-closure $(ldd $(which svn) | grep /libc.so | awk '{print $3}')
/nix/store/034a6h4vpz9kds5r6kzb9lhh81mscw43-libgnomeprintui-2.8.2
/nix/store/15l3yi0d45prm7a82pcrknxdh6nzmxza-gawk-3.1.4
...Note that ldd is a command that prints out the dynamic libraries used by an ELF executable.
Make a picture of the runtime dependency graph of the current user environment:
$ nix-store -q --graph ~/.nix-profile | dot -Tps > graph.ps $ gv graph.ps
Show every garbage collector root that points to a store path that depends on svn:
$ nix-store -q --roots $(which svn) /nix/var/nix/profiles/default-81-link /nix/var/nix/profiles/default-82-link /nix/var/nix/profiles/per-user/eelco/profile-97-link
--add--verifyThe operation --verify verifies the internal consistency of the Nix database, and the consistency between the Nix database and the Nix store. Any inconsistencies encountered are automatically repaired. Inconsistencies are generally the result of the Nix store or database being modified by non-Nix tools, or of bugs in Nix itself.
This operation has the following options:
--check-contentsChecks that the contents of every valid store path has not been altered by computing a SHA-256 hash of the contents and comparing it with the hash stored in the Nix database at build time. Paths that have been modified are printed out. For large stores, --check-contents is obviously quite slow.
--repairIf any valid path is missing from the store, or (if --check-contents is given) the contents of a valid path has been modified, then try to repair the path by redownloading it. See nix-store --repair-path for details.
--verify-path--repair-pathThe operation --repair-path attempts to “repair” the specified paths by redownloading them using the available substituters. If no substitutes are available, then repair is not possible.
$ nix-store --verify-path /nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13 path `/nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13' was modified! expected hash `2db57715ae90b7e31ff1f2ecb8c12ec1cc43da920efcbe3b22763f36a1861588', got `481c5aa5483ebc97c20457bb8bca24deea56550d3985cda0027f67fe54b808e4' $ nix-store --repair-path /nix/store/dj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13 fetching path `/nix/store/d7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13'... …
--dumpThe operation --dump produces a NAR (Nix ARchive) file containing the contents of the file system tree rooted at path. The archive is written to standard output.
A NAR archive is like a TAR or Zip archive, but it contains only the information that Nix considers important. For instance, timestamps are elided because all files in the Nix store have their timestamp set to 0 anyway. Likewise, all permissions are left out except for the execute bit, because all files in the Nix store have 644 or 755 permission.
Also, a NAR archive is canonical, meaning that “equal” paths always produce the same NAR archive. For instance, directory entries are always sorted so that the actual on-disk order doesn’t influence the result. This means that the cryptographic hash of a NAR dump of a path is usable as a fingerprint of the contents of the path. Indeed, the hashes of store paths stored in Nix’s database (see nix-store -q --hash) are SHA-256 hashes of the NAR dump of each store path.
NAR archives support filenames of unlimited length and 64-bit file sizes. They can contain regular files, directories, and symbolic links, but not other types of files (such as device nodes).
A Nix archive can be unpacked using nix-store --restore.
--exportThe operation --export writes a serialisation of the specified store paths to standard output in a format that can be imported into another Nix store with nix-store --import. This is like nix-store --dump, except that the NAR archive produced by that command doesn’t contain the necessary meta-information to allow it to be imported into another Nix store (namely, the set of references of the path).
This command does not produce a closure of the specified paths, so if a store path references other store paths that are missing in the target Nix store, the import will fail. To copy a whole closure, do something like:
$ nix-store --export $(nix-store -qR paths) > outTo import the whole closure again, run:
$ nix-store --import < out
--importThe operation --import reads a serialisation of a set of store paths produced by nix-store --export from standard input and adds those store paths to the Nix store. Paths that already exist in the Nix store are ignored. If a path refers to another path that doesn’t exist in the Nix store, the import fails.
--optimiseThe operation --optimise reduces Nix store disk space usage by finding identical files in the store and hard-linking them to each other. It typically reduces the size of the store by something like 25-35%. Only regular files and symlinks are hard-linked in this manner. Files are considered identical when they have the same NAR archive serialisation: that is, regular files must have the same contents and permission (executable or non-executable), and symlinks must have the same contents.
After completion, or when the command is interrupted, a report on the achieved savings is printed on standard error.
Use -vv or -vvv to get some progress indication.
--read-logThe operation --read-log prints the build log of the specified store paths on standard output. The build log is whatever the builder of a derivation wrote to standard output and standard error. If a store path is not a derivation, the deriver of the store path is used.
Build logs are kept in /nix/var/log/nix/drvs. However, there is no guarantee that a build log is available for any particular store path. For instance, if the path was downloaded as a pre-built binary through a substitute, then the log is unavailable.
--print-envThe operation --print-env prints out the environment of a derivation in a format that can be evaluated by a shell. The command line arguments of the builder are placed in the variable _args.
$ nix-store --print-env $(nix-instantiate '<nixpkgs>' -A firefox)
…
export src; src='/nix/store/plpj7qrwcz94z2psh6fchsi7s8yihc7k-firefox-12.0.source.tar.bz2'
export stdenv; stdenv='/nix/store/7c8asx3yfrg5dg1gzhzyq2236zfgibnn-stdenv'
export system; system='x86_64-linux'
export _args; _args='-e /nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25c-default-builder.sh'
--generate-binary-cache-keyThis command generates an Ed25519 key pair that can be used to create a signed binary cache. It takes three mandatory parameters:
A key name, such as cache.example.org-1, that is used to look up keys on the client when it verifies signatures. It can be anything, but it’s suggested to use the host name of your cache (e.g. cache.example.org) with a suffix denoting the number of the key (to be incremented every time you need to revoke a key).
The file name where the secret key is to be stored.
The file name where the public key is to be stored.
This section lists utilities that you can use when you work with Nix.
nix-channel { --add url [name] | --remove name | --list | --update [names...] | --rollback [generation] }
A Nix channel is a mechanism that allows you to automatically stay up-to-date with a set of pre-built Nix expressions. A Nix channel is just a URL that points to a place containing both a set of Nix expressions and a pointer to a binary cache. See also Chapter 12, Channels.
This command has the following operations:
--add url [name]Adds a channel named name with URL url to the list of subscribed channels. If name is omitted, it defaults to the last component of url, with the suffixes -stable or -unstable removed.
--remove nameRemoves the channel named name from the list of subscribed channels.
--listPrints the names and URLs of all subscribed channels on standard output.
--update [names…]Downloads the Nix expressions of all subscribed channels (or only those included in names if specified) and makes them the default for nix-env operations (by symlinking them from the directory ~/.nix-defexpr).
--rollback [generation]Reverts the previous call to nix-channel --update. Optionally, you can specify a specific channel generation number to restore.
Note that --add does not automatically perform an update.
The list of subscribed channels is stored in ~/.nix-channels.
To subscribe to the Nixpkgs channel and install the GNU Hello package:
$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable $ nix-channel --update $ nix-env -iA nixpkgs.hello
You can revert channel updates using --rollback:
$ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.nixpkgsVersion'
"14.04.527.0e935f1"
$ nix-channel --rollback
switching from generation 483 to 482
$ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.nixpkgsVersion'
"14.04.526.dbadfad"
/nix/var/nix/profiles/per-user/username/channelsnix-channel uses a nix-env profile to keep track of previous versions of the subscribed channels. Every time you run nix-channel --update, a new channel generation (that is, a symlink to the channel Nix expressions in the Nix store) is created. This enables nix-channel --rollback to revert to previous versions.
~/.nix-defexpr/channelsThis is a symlink to /nix/var/nix/profiles/per-user/. It ensures that nix-env can find your channels. In a multi-user installation, you may also have username/channels~/.nix-defexpr/channels_root, which links to the channels of the root user.
A channel URL should point to a directory containing the following files:
nixexprs.tar.xzA tarball containing Nix expressions and files referenced by them (such as build scripts and patches). At the top level, the tarball should contain a single directory. That directory must contain a file default.nix that serves as the channel’s “entry point”.
binary-cache-urlA file containing the URL to a binary cache (such as https://cache.nixos.org). Nix will automatically check this cache for pre-built binaries, if the user has sufficient rights to add binary caches. For instance, in a multi-user Nix setup, the binary caches provided by the channels of the root user are used automatically, but caches corresponding to the channels of non-root users are ignored.
nix-collect-garbage [--delete-old] [-d] [--delete-older-than period] [--max-freed bytes] [--dry-run]
The command nix-collect-garbage is mostly an alias of nix-store --gc, that is, it deletes all unreachable paths in the Nix store to clean up your system. However, it provides two additional options: -d (--delete-old), which deletes all old generations of all profiles in /nix/var/nix/profiles by invoking nix-env --delete-generations old on all profiles (of course, this makes rollbacks to previous configurations impossible); and --delete-older-than period, where period is a value such as 30d, which deletes all generations older than the specified number of days in all profiles in /nix/var/nix/profiles (except for the generations that were active at that point in time).
nix-copy-closure [ --to | --from ] [--gzip] [--include-outputs] [ --use-substitutes | -s ] [-v] user@machine paths
nix-copy-closure gives you an easy and efficient way to exchange software between machines. Given one or more Nix store paths on the local machine, nix-copy-closure computes the closure of those paths (i.e. all their dependencies in the Nix store), and copies all paths in the closure to the remote machine via the ssh (Secure Shell) command. With the --from, the direction is reversed: the closure of paths on a remote machine is copied to the Nix store on the local machine.
This command is efficient because it only sends the store paths that are missing on the target machine.
Since nix-copy-closure calls ssh, you may be asked to type in the appropriate password or passphrase. In fact, you may be asked twice because nix-copy-closure currently connects twice to the remote machine, first to get the set of paths missing on the target machine, and second to send the dump of those paths. If this bothers you, use ssh-agent.
--toCopy the closure of paths from the local Nix store to the Nix store on machine. This is the default.
--fromCopy the closure of paths from the Nix store on machine to the local Nix store.
--gzipEnable compression of the SSH connection.
--include-outputsAlso copy the outputs of store derivations included in the closure.
--use-substitutes / -sAttempt to download missing paths on the target machine using Nix’s substitute mechanism. Any paths that cannot be substituted on the target are still copied normally from the source. This is useful, for instance, if the connection between the source and target machine is slow, but the connection between the target machine and nixos.org (the default binary cache server) is fast.
-vShow verbose output.
Copy Firefox with all its dependencies to a remote machine:
$ nix-copy-closure --to alice@itchy.labs $(type -tP firefox)
Copy Subversion from a remote machine and then install it into a user environment:
$ nix-copy-closure --from alice@itchy.labs \
/nix/store/0dj0503hjxy5mbwlafv1rsbdiyx1gkdy-subversion-1.4.4
$ nix-env -i /nix/store/0dj0503hjxy5mbwlafv1rsbdiyx1gkdy-subversion-1.4.4
nix-hash [--flat] [--base32] [--truncate] [--type hashAlgo] path...
nix-hash --to-base16 hash...
nix-hash --to-base32 hash...
The command nix-hash computes the cryptographic hash of the contents of each path and prints it on standard output. By default, it computes an MD5 hash, but other hash algorithms are available as well. The hash is printed in hexadecimal. To generate the same hash as nix-prefetch-url you have to specify multiple arguments, see below for an example.
The hash is computed over a serialisation of each path: a dump of the file system tree rooted at the path. This allows directories and symlinks to be hashed as well as regular files. The dump is in the NAR format produced by nix-store --dump. Thus, nix-hash yields the same cryptographic hash as pathnix-store --dump .path | md5sum
--flatPrint the cryptographic hash of the contents of each regular file path. That is, do not compute the hash over the dump of path. The result is identical to that produced by the GNU commands md5sum and sha1sum.
--base32Print the hash in a base-32 representation rather than hexadecimal. This base-32 representation is more compact and can be used in Nix expressions (such as in calls to fetchurl).
--truncateTruncate hashes longer than 160 bits (such as SHA-256) to 160 bits.
--type hashAlgoUse the specified cryptographic hash algorithm, which can be one of md5, sha1, and sha256.
--to-base16Don’t hash anything, but convert the base-32 hash representation hash to hexadecimal.
--to-base32Don’t hash anything, but convert the hexadecimal hash representation hash to base-32.
Computing the same hash as nix-prefetch-url:
$ nix-prefetch-url file://<(echo test) 1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj $ nix-hash --type sha256 --flat --base32 <(echo test) 1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
Computing hashes:
$ mkdir test $ echo "hello" > test/world $ nix-hash test/ (MD5 hash; default) 8179d3caeff1869b5ba1744e5a245c04 $ nix-store --dump test/ | md5sum (for comparison) 8179d3caeff1869b5ba1744e5a245c04 - $ nix-hash --type sha1 test/ e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6 $ nix-hash --type sha1 --base32 test/ nvd61k9nalji1zl9rrdfmsmvyyjqpzg4 $ nix-hash --type sha256 --flat test/ error: reading file `test/': Is a directory $ nix-hash --type sha256 --flat test/world 5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03
Converting between hexadecimal and base-32:
$ nix-hash --type sha1 --to-base32 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4 $ nix-hash --type sha1 --to-base16 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
nix-instantiate [ --parse | --eval [--strict] [--json] [--xml] ] [--read-write-mode] [--arg name value] [ { --attr | -A } attrPath ] [--add-root path] [--indirect] [ --expr | -E ] files...
nix-instantiate --find-file files...
The command nix-instantiate generates store derivations from (high-level) Nix expressions. It evaluates the Nix expressions in each of files (which defaults to ./default.nix). Each top-level expression should evaluate to a derivation, a list of derivations, or a set of derivations. The paths of the resulting store derivations are printed on standard output.
If files is the character -, then a Nix expression will be read from standard input.
See also Chapter 17, Common Options for a list of common options.
--add-root path, --indirectSee the corresponding options in nix-store.
--parseJust parse the input files, and print their abstract syntax trees on standard output in ATerm format.
--evalJust parse and evaluate the input files, and print the resulting values on standard output. No instantiation of store derivations takes place.
--find-fileLook up the given files in Nix’s search path (as specified by the NIX_PATH environment variable). If found, print the corresponding absolute paths on standard output. For instance, if NIX_PATH is nixpkgs=/home/alice/nixpkgs, then nix-instantiate --find-file nixpkgs/default.nix will print /home/alice/nixpkgs/default.nix.
--strictWhen used with --eval, recursively evaluate list elements and attributes. Normally, such sub-expressions are left unevaluated (since the Nix expression language is lazy).
--jsonWhen used with --eval, print the resulting value as an JSON representation of the abstract syntax tree rather than as an ATerm.
--xmlWhen used with --eval, print the resulting value as an XML representation of the abstract syntax tree rather than as an ATerm. The schema is the same as that used by the toXML built-in.
--read-write-modeWhen used with --eval, perform evaluation in read/write mode so nix language features that require it will still work (at the cost of needing to do instantiation of every evaluated derivation).
Instantiating store derivations from a Nix expression, and building them using nix-store:
$ nix-instantiate test.nix (instantiate)
/nix/store/cigxbmvy6dzix98dxxh9b6shg7ar5bvs-perl-BerkeleyDB-0.26.drv
$ nix-store -r $(nix-instantiate test.nix) (build)
...
/nix/store/qhqk4n8ci095g3sdp93x7rgwyh9rdvgk-perl-BerkeleyDB-0.26 (output path)
$ ls -l /nix/store/qhqk4n8ci095g3sdp93x7rgwyh9rdvgk-perl-BerkeleyDB-0.26
dr-xr-xr-x 2 eelco users 4096 1970-01-01 01:00 lib
...
You can also give a Nix expression on the command line:
$ nix-instantiate -E 'with import <nixpkgs> { }; hello'
/nix/store/j8s4zyv75a724q38cb0r87rlczaiag4y-hello-2.8.drv
This is equivalent to:
$ nix-instantiate '<nixpkgs>' -A hello
Parsing and evaluating Nix expressions:
$ nix-instantiate --parse -E '1 + 2' 1 + 2 $ nix-instantiate --eval -E '1 + 2' 3 $ nix-instantiate --eval --xml -E '1 + 2' <?xml version='1.0' encoding='utf-8'?> <expr> <int value="3" /> </expr>
The difference between non-strict and strict evaluation:
$ nix-instantiate --eval --xml -E 'rec { x = "foo"; y = x; }'
...
<attr name="x">
<string value="foo" />
</attr>
<attr name="y">
<unevaluated />
</attr>
... Note that y is left unevaluated (the XML representation doesn’t attempt to show non-normal forms).
$ nix-instantiate --eval --xml --strict -E 'rec { x = "foo"; y = x; }'
...
<attr name="x">
<string value="foo" />
</attr>
<attr name="y">
<string value="foo" />
</attr>
...
nix-prefetch-url [--version] [--type hashAlgo] [--print-path] [--unpack] [--name name] url [hash]
The command nix-prefetch-url downloads the file referenced by the URL url, prints its cryptographic hash, and copies it into the Nix store. The file name in the store is hash-baseNamebaseName is everything following the final slash in url.
This command is just a convenience for Nix expression writers. Often a Nix expression fetches some source distribution from the network using the fetchurl expression contained in Nixpkgs. However, fetchurl requires a cryptographic hash. If you don't know the hash, you would have to download the file first, and then fetchurl would download it again when you build your Nix expression. Since fetchurl uses the same name for the downloaded file as nix-prefetch-url, the redundant download can be avoided.
If hash is specified, then a download is not performed if the Nix store already contains a file with the same hash and base name. Otherwise, the file is downloaded, and an error if signaled if the actual hash of the file does not match the specified hash.
This command prints the hash on standard output. Additionally, if the option --print-path is used, the path of the downloaded file in the Nix store is also printed.
--type hashAlgoUse the specified cryptographic hash algorithm, which can be one of md5, sha1, and sha256.
--print-pathPrint the store path of the downloaded file on standard output.
--unpackUnpack the archive (which must be a tarball or zip file) and add the result to the Nix store. The resulting hash can be used with functions such as Nixpkgs’s fetchzip or fetchFromGitHub.
--name nameOverride the name of the file in the Nix store. By default, this is hash-basenamebasename is the last component of url. Overriding the name is necessary when basename contains characters that are not allowed in Nix store paths.
$ nix-prefetch-url ftp://ftp.gnu.org/pub/gnu/hello/hello-2.10.tar.gz 0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i $ nix-prefetch-url --print-path mirror://gnu/hello/hello-2.10.tar.gz 0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i /nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz $ nix-prefetch-url --unpack --print-path https://github.com/NixOS/patchelf/archive/0.8.tar.gz 079agjlv0hrv7fxnx9ngipx14gyncbkllxrp9cccnh3a50fxcmy7 /nix/store/19zrmhm3m40xxaw81c8cqm6aljgrnwj2-0.8.tar.gz
This section lists configuration files that you can use when you work with Nix.
Nix reads settings from two configuration files:
The system-wide configuration file sysconfdir/nix/nix.conf/etc/nix/nix.conf on most systems), or $NIX_CONF_DIR/nix.conf if NIX_CONF_DIR is set.
The user configuration file $XDG_CONFIG_HOME/nix/nix.conf, or ~/.config/nix/nix.conf if XDG_CONFIG_HOME is not set.
The configuration files consist of name = valueinclude , where pathpath is interpreted relative to the current conf file and a missing file is an error unless !include is used instead. Comments start with a # character. Here is an example configuration file:
keep-outputs = true # Nice for developers keep-derivations = true # Idem
You can override settings on the command line using the --option flag, e.g. --option keep-outputs false.
The following settings are currently available:
allowed-urisA list of URI prefixes to which access is allowed in restricted evaluation mode. For example, when set to https://github.com/NixOS, builtin functions such as fetchGit are allowed to access https://github.com/NixOS/patchelf.git.
allow-import-from-derivationBy default, Nix allows you to import from a derivation, allowing building at evaluation time. With this option set to false, Nix will throw an error when evaluating an expression that uses this feature, allowing users to ensure their evaluation will not require any builds to take place.
allow-new-privileges(Linux-specific.) By default, builders on Linux cannot acquire new privileges by calling setuid/setgid programs or programs that have file capabilities. For example, programs such as sudo or ping will fail. (Note that in sandbox builds, no such programs are available unless you bind-mount them into the sandbox via the sandbox-paths option.) You can allow the use of such programs by enabling this option. This is impure and usually undesirable, but may be useful in certain scenarios (e.g. to spin up containers or set up userspace network interfaces in tests).
allowed-usersA list of names of users (separated by whitespace) that are allowed to connect to the Nix daemon. As with the trusted-users option, you can specify groups by prefixing them with @. Also, you can allow all users by specifying *. The default is *.
Note that trusted users are always allowed to connect.
auto-optimise-storeIf set to true, Nix automatically detects files in the store that have identical contents, and replaces them with hard links to a single copy. This saves disk space. If set to false (the default), you can still run nix-store --optimise to get rid of duplicate files.
buildersA list of machines on which to perform builds. See Chapter 16, Remote Builds for details.
builders-use-substitutesIf set to true, Nix will instruct remote build machines to use their own binary substitutes if available. In practical terms, this means that remote hosts will fetch as many build dependencies as possible from their own substitutes (e.g, from cache.nixos.org), instead of waiting for this host to upload them all. This can drastically reduce build times if the network connection between this computer and the remote build host is slow. Defaults to false.
build-users-groupThis options specifies the Unix group containing the Nix build user accounts. In multi-user Nix installations, builds should not be performed by the Nix account since that would allow users to arbitrarily modify the Nix store and database by supplying specially crafted builders; and they cannot be performed by the calling user since that would allow him/her to influence the build result.
Therefore, if this option is non-empty and specifies a valid group, builds will be performed under the user accounts that are a member of the group specified here (as listed in /etc/group). Those user accounts should not be used for any other purpose!
Nix will never run two builds under the same user account at the same time. This is to prevent an obvious security hole: a malicious user writing a Nix expression that modifies the build result of a legitimate Nix expression being built by another user. Therefore it is good to have as many Nix build user accounts as you can spare. (Remember: uids are cheap.)
The build users should have permission to create files in the Nix store, but not delete them. Therefore, /nix/store should be owned by the Nix account, its group should be the group specified here, and its mode should be 1775.
If the build users group is empty, builds will be performed under the uid of the Nix process (that is, the uid of the caller if NIX_REMOTE is empty, the uid under which the Nix daemon runs if NIX_REMOTE is daemon). Obviously, this should not be used in multi-user settings with untrusted users.
compress-build-logIf set to true (the default), build logs written to /nix/var/log/nix/drvs will be compressed on the fly using bzip2. Otherwise, they will not be compressed.
connect-timeoutThe timeout (in seconds) for establishing connections in the binary cache substituter. It corresponds to curl’s --connect-timeout option.
coresSets the value of the NIX_BUILD_CORES environment variable in the invocation of builders. Builders can use this variable at their discretion to control the maximum amount of parallelism. For instance, in Nixpkgs, if the derivation attribute enableParallelBuilding is set to true, the builder passes the -j flag to GNU Make. It can be overridden using the N--cores command line switch and defaults to 1. The value 0 means that the builder should use all available CPU cores in the system.
extra-sandbox-pathsA list of additional paths appended to sandbox-paths. Useful if you want to extend its default value.
extra-platformsPlatforms other than the native one which this machine is capable of building for. This can be useful for supporting additional architectures on compatible machines: i686-linux can be built on x86_64-linux machines (and the default for this setting reflects this); armv7 is backwards-compatible with armv6 and armv5tel; some aarch64 machines can also natively run 32-bit ARM code; and qemu-user may be used to support non-native platforms (though this may be slow and buggy). Most values for this are not enabled by default because build systems will often misdetect the target platform and generate incompatible code, so you may wish to cross-check the results of using this option against proper natively-built versions of your derivations.
extra-substitutersAdditional binary caches appended to those specified in substituters. When used by unprivileged users, untrusted substituters (i.e. those not listed in trusted-substituters) are silently ignored.
fallbackIf set to true, Nix will fall back to building from source if a binary substitute fails. This is equivalent to the --fallback flag. The default is false.
fsync-metadataIf set to true, changes to the Nix store metadata (in /nix/var/nix/db) are synchronously flushed to disk. This improves robustness in case of system crashes, but reduces performance. The default is true.
hashed-mirrorsA list of web servers used by builtins.fetchurl to obtain files by hash. The default is http://tarballs.nixos.org/. Given a hash type ht and a base-16 hash h, Nix will try to download the file from hashed-mirror/. This allows files to be downloaded even if they have disappeared from their original URI. For example, given the default mirror ht/hhttp://tarballs.nixos.org/, when building the derivation
builtins.fetchurl {
url = https://example.org/foo-1.2.3.tar.xz;
sha256 = "2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae";
}
Nix will attempt to download this file from http://tarballs.nixos.org/sha256/2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae first. If it is not available there, if will try the original URI.
http-connectionsThe maximum number of parallel TCP connections used to fetch files from binary caches and by other downloads. It defaults to 25. 0 means no limit.
keep-build-logIf set to true (the default), Nix will write the build log of a derivation (i.e. the standard output and error of its builder) to the directory /nix/var/log/nix/drvs. The build log can be retrieved using the command nix-store -l path.
keep-derivationsIf true (default), the garbage collector will keep the derivations from which non-garbage store paths were built. If false, they will be deleted unless explicitly registered as a root (or reachable from other roots).
Keeping derivation around is useful for querying and traceability (e.g., it allows you to ask with what dependencies or options a store path was built), so by default this option is on. Turn it off to save a bit of disk space (or a lot if keep-outputs is also turned on).
keep-env-derivationsIf false (default), derivations are not stored in Nix user environments. That is, the derivation any build-time-only dependencies may be garbage-collected.
If true, when you add a Nix derivation to a user environment, the path of the derivation is stored in the user environment. Thus, the derivation will not be garbage-collected until the user environment generation is deleted (nix-env --delete-generations). To prevent build-time-only dependencies from being collected, you should also turn on keep-outputs.
The difference between this option and keep-derivations is that this one is “sticky”: it applies to any user environment created while this option was enabled, while keep-derivations only applies at the moment the garbage collector is run.
keep-outputsIf true, the garbage collector will keep the outputs of non-garbage derivations. If false (default), outputs will be deleted unless they are GC roots themselves (or reachable from other roots).
In general, outputs must be registered as roots separately. However, even if the output of a derivation is registered as a root, the collector will still delete store paths that are used only at build time (e.g., the C compiler, or source tarballs downloaded from the network). To prevent it from doing so, set this option to true.
max-build-log-sizeThis option defines the maximum number of bytes that a builder can write to its stdout/stderr. If the builder exceeds this limit, it’s killed. A value of 0 (the default) means that there is no limit.
max-freeThis option defines after how many free bytes to stop collecting garbage once the min-free condition gets triggered.
max-jobsThis option defines the maximum number of jobs that Nix will try to build in parallel. The default is 1. The special value auto causes Nix to use the number of CPUs in your system. It can be overridden using the --max-jobs (-j) command line switch.
max-silent-timeThis option defines the maximum number of seconds that a builder can go without producing any data on standard output or standard error. This is useful (for instance in an automated build system) to catch builds that are stuck in an infinite loop, or to catch remote builds that are hanging due to network problems. It can be overridden using the --max-silent-time command line switch.
The value 0 means that there is no timeout. This is also the default.
min-freeWhen the disk reaches min-free bytes of free disk space during a build, nix will start to garbage-collection until max-free bytes are available on the disk. A value of 0 (the default) means that this feature is disabled.
narinfo-cache-negative-ttlThe TTL in seconds for negative lookups. If a store path is queried from a substituter but was not found, there will be a negative lookup cached in the local disk cache database for the specified duration.
narinfo-cache-positive-ttlThe TTL in seconds for positive lookups. If a store path is queried from a substituter, the result of the query will be cached in the local disk cache database including some of the NAR metadata. The default TTL is a month, setting a shorter TTL for positive lookups can be useful for binary caches that have frequent garbage collection, in which case having a more frequent cache invalidation would prevent trying to pull the path again and failing with a hash mismatch if the build isn't reproducible.
netrc-fileIf set to an absolute path to a netrc file, Nix will use the HTTP authentication credentials in this file when trying to download from a remote host through HTTP or HTTPS. Defaults to $NIX_CONF_DIR/netrc.
The netrc file consists of a list of accounts in the following format:
machinemy-machineloginmy-usernamepasswordmy-password
For the exact syntax, see the curl documentation.
~ is not resolved. For example, ~/.netrc won't resolve to your home directory's .netrc.plugin-files A list of plugin files to be loaded by Nix. Each of these files will be dlopened by Nix, allowing them to affect execution through static initialization. In particular, these plugins may construct static instances of RegisterPrimOp to add new primops or constants to the expression language, RegisterStoreImplementation to add new store implementations, RegisterCommand to add new subcommands to the nix command, and RegisterSetting to add new nix config settings. See the constructors for those types for more details.
Since these files are loaded into the same address space as Nix itself, they must be DSOs compatible with the instance of Nix running at the time (i.e. compiled against the same headers, not linked to any incompatible libraries). They should not be linked to any Nix libs directly, as those will be available already at load time.
If an entry in the list is a directory, all files in the directory are loaded as plugins (non-recursively).
pre-build-hookIf set, the path to a program that can set extra derivation-specific settings for this system. This is used for settings that can't be captured by the derivation model itself and are too variable between different versions of the same system to be hard-coded into nix.
The hook is passed the derivation path and, if sandboxes are enabled, the sandbox directory. It can then modify the sandbox and send a series of commands to modify various settings to stdout. The currently recognized commands are:
repeatHow many times to repeat builds to check whether they are deterministic. The default value is 0. If the value is non-zero, every build is repeated the specified number of times. If the contents of any of the runs differs from the previous ones, the build is rejected and the resulting store paths are not registered as “valid” in Nix’s database.
require-sigsIf set to true (the default), any non-content-addressed path added or copied to the Nix store (e.g. when substituting from a binary cache) must have a valid signature, that is, be signed using one of the keys listed in trusted-public-keys or secret-key-files. Set to false to disable signature checking.
restrict-evalIf set to true, the Nix evaluator will not allow access to any files outside of the Nix search path (as set via the NIX_PATH environment variable or the -I option), or to URIs outside of allowed-uri. The default is false.
sandboxIf set to true, builds will be performed in a sandboxed environment, i.e., they’re isolated from the normal file system hierarchy and will only see their dependencies in the Nix store, the temporary build directory, private versions of /proc, /dev, /dev/shm and /dev/pts (on Linux), and the paths configured with the sandbox-paths option. This is useful to prevent undeclared dependencies on files in directories such as /usr/bin. In addition, on Linux, builds run in private PID, mount, network, IPC and UTS namespaces to isolate them from other processes in the system (except that fixed-output derivations do not run in private network namespace to ensure they can access the network).
Currently, sandboxing only work on Linux and macOS. The use of a sandbox requires that Nix is run as root (so you should use the “build users” feature to perform the actual builds under different users than root).
If this option is set to relaxed, then fixed-output derivations and derivations that have the __noChroot attribute set to true do not run in sandboxes.
The default is false.
sandbox-dev-shm-sizeThis option determines the maximum size of the tmpfs filesystem mounted on /dev/shm in Linux sandboxes. For the format, see the description of the size option of tmpfs in mount(8). The default is 50%.
sandbox-pathsA list of paths bind-mounted into Nix sandbox environments. You can use the syntax target=source/bin=/nix-bin will mount the path /nix-bin as /bin inside the sandbox. If source is followed by ?, then it is not an error if source does not exist; for example, /dev/nvidiactl? specifies that /dev/nvidiactl will only be mounted in the sandbox if it exists in the host filesystem.
Depending on how Nix was built, the default value for this option may be empty or provide /bin/sh as a bind-mount of bash.
secret-key-filesA whitespace-separated list of files containing secret (private) keys. These are used to sign locally-built paths. They can be generated using nix-store --generate-binary-cache-key. The corresponding public key can be distributed to other users, who can add it to trusted-public-keys in their nix.conf.
show-traceCauses Nix to print out a stack trace in case of Nix expression evaluation errors.
substituteIf set to true (default), Nix will use binary substitutes if available. This option can be disabled to force building from source.
substitutersA list of URLs of substituters, separated by whitespace. The default is https://cache.nixos.org.
systemThis option specifies the canonical Nix system name of the current installation, such as i686-linux or x86_64-darwin. Nix can only build derivations whose system attribute equals the value specified here. In general, it never makes sense to modify this value from its default, since you can use it to ‘lie’ about the platform you are building on (e.g., perform a Mac OS build on a Linux machine; the result would obviously be wrong). It only makes sense if the Nix binaries can run on multiple platforms, e.g., ‘universal binaries’ that run on x86_64-linux and i686-linux.
It defaults to the canonical Nix system name detected by configure at build time.
timeoutThis option defines the maximum number of seconds that a builder can run. This is useful (for instance in an automated build system) to catch builds that are stuck in an infinite loop but keep writing to their standard output or standard error. It can be overridden using the --timeout command line switch.
The value 0 means that there is no timeout. This is also the default.
trusted-public-keysA whitespace-separated list of public keys. When paths are copied from another Nix store (such as a binary cache), they must be signed with one of these keys. For example: cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.nixos.org-1:CNHJZBh9K4tP3EKF6FkkgeVYsS3ohTl+oS0Qa8bezVs=.
trusted-substitutersA list of URLs of substituters, separated by whitespace. These are not used by default, but can be enabled by users of the Nix daemon by specifying --option substituters on the command line. Unprivileged users are only allowed to pass a subset of the URLs listed in urlssubstituters and trusted-substituters.
trusted-usersA list of names of users (separated by whitespace) that have additional rights when connecting to the Nix daemon, such as the ability to specify additional binary caches, or to import unsigned NARs. You can also specify groups by prefixing them with @; for instance, @wheel means all users in the wheel group. The default is root.
trusted-users is essentially equivalent to giving that user root access to the system. For example, the user can set sandbox-paths and thereby obtain read access to directories that are otherwise inacessible to them.
binary-cachesDeprecated: binary-caches is now an alias to substituters.
binary-cache-public-keysDeprecated: binary-cache-public-keys is now an alias to trusted-public-keys.
build-compress-logDeprecated: build-compress-log is now an alias to compress-build-log.
build-coresDeprecated: build-cores is now an alias to cores.
build-extra-chroot-dirsDeprecated: build-extra-chroot-dirs is now an alias to extra-sandbox-paths.
build-extra-sandbox-pathsDeprecated: build-extra-sandbox-paths is now an alias to extra-sandbox-paths.
build-fallbackDeprecated: build-fallback is now an alias to fallback.
build-max-jobsDeprecated: build-max-jobs is now an alias to max-jobs.
build-max-log-sizeDeprecated: build-max-log-size is now an alias to max-build-log-size.
build-max-silent-timeDeprecated: build-max-silent-time is now an alias to max-silent-time.
build-repeatDeprecated: build-repeat is now an alias to repeat.
build-timeoutDeprecated: build-timeout is now an alias to timeout.
build-use-chrootDeprecated: build-use-chroot is now an alias to sandbox.
build-use-sandboxDeprecated: build-use-sandbox is now an alias to sandbox.
build-use-substitutesDeprecated: build-use-substitutes is now an alias to substitute.
gc-keep-derivationsDeprecated: gc-keep-derivations is now an alias to keep-derivations.
gc-keep-outputsDeprecated: gc-keep-outputs is now an alias to keep-outputs.
env-keep-derivationsDeprecated: env-keep-derivations is now an alias to keep-env-derivations.
extra-binary-cachesDeprecated: extra-binary-caches is now an alias to extra-substituters.
trusted-binary-cachesDeprecated: trusted-binary-caches is now an alias to trusted-substituters.
A description of a build action. The result of a derivation is a store object. Derivations are typically specified in Nix expressions using the derivation primitive. These are translated into low-level store derivations (implicitly by nix-env and nix-build, or explicitly by nix-instantiate).
The location in the file system where store objects live. Typically /nix/store.
The location in the file system of a store object, i.e., an immediate child of the Nix store directory.
A file that is an immediate child of the Nix store directory. These can be regular files, but also entire directory trees. Store objects can be sources (objects copied from outside of the store), derivation outputs (objects produced by running a build action), or derivations (files describing a build action).
A substitute is a command invocation stored in the Nix database that describes how to build a store object, bypassing the normal build mechanism (i.e., derivations). Typically, the substitute builds the store object by downloading a pre-built version of the store object from some server.
The assumption that equal Nix derivations when run always produce the same output. This cannot be guaranteed in general (e.g., a builder can rely on external inputs such as the network or the system time) but the Nix model assumes it.
A high-level description of software packages and compositions thereof. Deploying software using Nix entails writing Nix expressions for your packages. Nix expressions are translated to derivations that are stored in the Nix store. These derivations can then be built.
A store path P is said to have a reference to a store path Q if the store object at P contains the path Q somewhere. The references of a store path are the set of store paths to which it has a reference.
A derivation can reference other derivations and sources (but not output paths), whereas an output path only references other output paths.
A store path Q is reachable from another store path P if Q is in the closure of the references relation.
The closure of a store path is the set of store paths that are directly or indirectly “reachable” from that store path; that is, it’s the closure of the path under the references relation. For a package, the closure of its derivation is equivalent to the build-time dependencies, while the closure of its output path is equivalent to its runtime dependencies. For correct deployment it is necessary to deploy whole closures, since otherwise at runtime files could be missing. The command nix-store -qR prints out closures of store paths.
As an example, if the store object at path P contains a reference to path Q, then Q is in the closure of P. Further, if Q references R then R is also in the closure of P.
A store path produced by a derivation.
The deriver of an output path is the store derivation that built it.
A store path is considered valid if it exists in the file system, is listed in the Nix database as being valid, and if all paths in its closure are also valid.
An automatically generated store object that consists of a set of symlinks to “active” applications, i.e., other store paths. These are generated automatically by nix-env. See Chapter 10, Profiles.
A symlink to the current user environment of a user, e.g., /nix/var/nix/profiles/default.
A Nix ARchive. This is a serialisation of a path in the Nix store. It can contain regular files, directories and symbolic links. NARs are generated and unpacked using nix-store --dump and nix-store --restore.
This section provides some notes on how to hack on Nix. To get the latest version of Nix from GitHub:
$ git clone git://github.com/NixOS/nix.git $ cd nix
To build it and its dependencies:
$ nix-build release.nix -A build.x86_64-linux
To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:
$ nix-shell
To build Nix itself in this shell:
[nix-shell]$ ./bootstrap.sh [nix-shell]$ configurePhase [nix-shell]$ make
To install it in $(pwd)/inst and test it:
[nix-shell]$ make install [nix-shell]$ make installcheck
This is primarily a bug fix release. It also reduces memory consumption in certain situations. In addition, it has the following new features:
The Nix installer will no longer default to the Multi-User installation for macOS. You can still instruct the installer to run in multi-user mode.
The Nix installer now supports performing a Multi-User installation for Linux computers which are running systemd. You can select a Multi-User installation by passing the --daemon flag to the installer: sh <(curl https://nixos.org/nix/install) --daemon.
The multi-user installer cannot handle systems with SELinux. If your system has SELinux enabled, you can force the installer to run in single-user mode.
New builtin functions: builtins.bitAnd, builtins.bitOr, builtins.bitXor, builtins.fromTOML, builtins.concatMap, builtins.mapAttrs.
The S3 binary cache store now supports uploading NARs larger than 5 GiB.
The S3 binary cache store now supports uploading to S3-compatible services with the endpoint option.
The flag --fallback is no longer required to recover from disappeared NARs in binary caches.
nix-daemon now respects --store.
nix run now respects nix-support/propagated-user-env-packages.
This release has contributions from Adrien Devresse, Aleksandr Pashkov, Alexandre Esteves, Amine Chikhaoui, Andrew Dunham, Asad Saeeduddin, aszlig, Ben Challenor, Ben Gamari, Benjamin Hipple, Bogdan Seniuc, Corey O'Connor, Daiderd Jordan, Daniel Peebles, Daniel Poelzleithner, Danylo Hlynskyi, Dmitry Kalinkin, Domen Kožar, Doug Beardsley, Eelco Dolstra, Erik Arvstedt, Félix Baylac-Jacqué, Gleb Peregud, Graham Christensen, Guillaume Maudoux, Ivan Kozik, John Arnold, Justin Humm, Linus Heckemann, Lorenzo Manacorda, Matthew Justin Bauer, Matthew O'Gorman, Maximilian Bosch, Michael Bishop, Michael Fiano, Michael Mercier, Michael Raskin, Michael Weiss, Nicolas Dudebout, Peter Simons, Ryan Trinkle, Samuel Dionne-Riel, Sean Seefried, Shea Levy, Symphorien Gibol, Tim Engler, Tim Sears, Tuomas Tynkkynen, volth, Will Dietz, Yorick van Pelt and zimbatm.
The following incompatible changes have been made:
The manifest-based substituter mechanism (download-using-manifests) has been removed. It has been superseded by the binary cache substituter mechanism since several years. As a result, the following programs have been removed:
nix-pull
nix-generate-patches
bsdiff
bspatch
The “copy from other stores” substituter mechanism (copy-from-other-stores and the NIX_OTHER_STORES environment variable) has been removed. It was primarily used by the NixOS installer to copy available paths from the installation medium. The replacement is to use a chroot store as a substituter (e.g. --substituters /mnt), or to build into a chroot store (e.g. --store /mnt --substituters /).
The command nix-push has been removed as part of the effort to eliminate Nix's dependency on Perl. You can use nix copy instead, e.g. nix copy --to file:///tmp/my-binary-cache paths…
The “nested” log output feature (--log-type pretty) has been removed. As a result, nix-log2xml was also removed.
OpenSSL-based signing has been removed. This feature was never well-supported. A better alternative is provided by the secret-key-files and trusted-public-keys options.
Failed build caching has been removed. This feature was introduced to support the Hydra continuous build system, but Hydra no longer uses it.
nix-mode.el has been removed from Nix. It is now a separate repository and can be installed through the MELPA package repository.
This release has the following new features:
It introduces a new command named nix, which is intended to eventually replace all nix-* commands with a more consistent and better designed user interface. It currently provides replacements for some (but not all) of the functionality provided by nix-store, nix-build, nix-shell -p, nix-env -qa, nix-instantiate --eval, nix-push and nix-copy-closure. It has the following major features:
Unlike the legacy commands, it has a consistent way to refer to packages and package-like arguments (like store paths). For example, the following commands all copy the GNU Hello package to a remote machine:
nix copy --to ssh://machine nixpkgs.hello
nix copy --to ssh://machine /nix/store/0i2jd68mp5g6h2sa5k9c85rb80sn8hi9-hello-2.10
nix copy --to ssh://machine '(with import <nixpkgs> {}; hello)'By contrast, nix-copy-closure only accepted store paths as arguments.
It is self-documenting: --help shows all available command-line arguments. If --help is given after a subcommand, it shows examples for that subcommand. nix --help-config shows all configuration options.
It is much less verbose. By default, it displays a single-line progress indicator that shows how many packages are left to be built or downloaded, and (if there are running builds) the most recent line of builder output. If a build fails, it shows the last few lines of builder output. The full build log can be retrieved using nix log.
It provides all nix.conf configuration options as command line flags. For example, instead of --option http-connections 100 you can write --http-connections 100. Boolean options can be written as -- or foo--no- (e.g. foo--no-auto-optimise-store).
Many subcommands have a --json flag to write results to stdout in JSON format.
It provides the following high-level (“porcelain”) subcommands:
nix build is a replacement for nix-build.
nix run executes a command in an environment in which the specified packages are available. It is (roughly) a replacement for nix-shell -p. Unlike that command, it does not execute the command in a shell, and has a flag (-c) that specifies the unquoted command line to be executed.
It is particularly useful in conjunction with chroot stores, allowing Linux users who do not have permission to install Nix in /nix/store to still use binary substitutes that assume /nix/store. For example,
nix run --store ~/my-nix nixpkgs.hello -c hello --greeting 'Hi everybody!'
downloads (or if not substitutes are available, builds) the GNU Hello package into ~/my-nix/nix/store, then runs hello in a mount namespace where ~/my-nix/nix/store is mounted onto /nix/store.
nix search replaces nix-env -qa. It searches the available packages for occurrences of a search string in the attribute name, package name or description. Unlike nix-env -qa, it has a cache to speed up subsequent searches.
nix copy copies paths between arbitrary Nix stores, generalising nix-copy-closure and nix-push.
nix repl replaces the external program nix-repl. It provides an interactive environment for evaluating and building Nix expressions. Note that it uses linenoise-ng instead of GNU Readline.
nix upgrade-nix upgrades Nix to the latest stable version. This requires that Nix is installed in a profile. (Thus it won’t work on NixOS, or if it’s installed outside of the Nix store.)
nix verify checks whether store paths are unmodified and/or “trusted” (see below). It replaces nix-store --verify and nix-store --verify-path.
nix log shows the build log of a package or path. If the build log is not available locally, it will try to obtain it from the configured substituters (such as cache.nixos.org, which now provides build logs).
nix edit opens the source code of a package in your editor.
nix eval replaces nix-instantiate --eval.
nix why-depends shows why one store path has another in its closure. This is primarily useful to finding the causes of closure bloat. For example,
nix why-depends nixpkgs.vlc nixpkgs.libdrm.dev
shows a chain of files and fragments of file contents that cause the VLC package to have the “dev” output of libdrm in its closure — an undesirable situation.
nix path-info shows information about store paths, replacing nix-store -q. A useful feature is the option --closure-size (-S). For example, the following command show the closure sizes of every path in the current NixOS system closure, sorted by size:
nix path-info -rS /run/current-system | sort -nk2
nix optimise-store replaces nix-store --optimise. The main difference is that it has a progress indicator.
A number of low-level (“plumbing”) commands are also available:
nix ls-store and nix ls-nar list the contents of a store path or NAR file. The former is primarily useful in conjunction with remote stores, e.g.
nix ls-store --store https://cache.nixos.org/ -lR /nix/store/0i2jd68mp5g6h2sa5k9c85rb80sn8hi9-hello-2.10
lists the contents of path in a binary cache.
nix cat-store and nix cat-nar allow extracting a file from a store path or NAR file.
nix dump-path writes the contents of a store path to stdout in NAR format. This replaces nix-store --dump.
nix show-derivation displays a store derivation in JSON format. This is an alternative to pp-aterm.
nix add-to-store replaces nix-store --add.
nix sign-paths signs store paths.
nix copy-sigs copies signatures from one store to another.
nix show-config shows all configuration options and their current values.
The store abstraction that Nix has had for a long time to support store access via the Nix daemon has been extended significantly. In particular, substituters (which used to be external programs such as download-from-binary-cache) are now subclasses of the abstract Store class. This allows many Nix commands to operate on such store types. For example, nix path-info shows information about paths in your local Nix store, while nix path-info --store https://cache.nixos.org/ shows information about paths in the specified binary cache. Similarly, nix-copy-closure, nix-push and substitution are all instances of the general notion of copying paths between different kinds of Nix stores.
Stores are specified using an URI-like syntax, e.g. https://cache.nixos.org/ or ssh://machine. The following store types are supported:
LocalStore (stori URI local or an absolute path) and the misnamed RemoteStore (daemon) provide access to a local Nix store, the latter via the Nix daemon. You can use auto or the empty string to auto-select a local or daemon store depending on whether you have write permission to the Nix store. It is no longer necessary to set the NIX_REMOTE environment variable to use the Nix daemon.
As noted above, LocalStore now supports chroot builds, allowing the “physical” location of the Nix store (e.g. /home/alice/nix/store) to differ from its “logical” location (typically /nix/store). This allows non-root users to use Nix while still getting the benefits from prebuilt binaries from cache.nixos.org.
BinaryCacheStore is the abstract superclass of all binary cache stores. It supports writing build logs and NAR content listings in JSON format.
HttpBinaryCacheStore (http://, https://) supports binary caches via HTTP or HTTPS. If the server supports PUT requests, it supports uploading store paths via commands such as nix copy.
LocalBinaryCacheStore (file://) supports binary caches in the local filesystem.
S3BinaryCacheStore (s3://) supports binary caches stored in Amazon S3, if enabled at compile time.
LegacySSHStore (ssh://) is used to implement remote builds and nix-copy-closure.
SSHStore (ssh-ng://) supports arbitrary Nix operations on a remote machine via the same protocol used by nix-daemon.
Security has been improved in various ways:
Nix now stores signatures for local store paths. When paths are copied between stores (e.g., copied from a binary cache to a local store), signatures are propagated.
Locally-built paths are signed automatically using the secret keys specified by the secret-key-files store option. Secret/public key pairs can be generated using nix-store --generate-binary-cache-key.
In addition, locally-built store paths are marked as “ultimately trusted”, but this bit is not propagated when paths are copied between stores.
Content-addressable store paths no longer require signatures — they can be imported into a store by unprivileged users even if they lack signatures.
The command nix verify checks whether the specified paths are trusted, i.e., have a certain number of trusted signatures, are ultimately trusted, or are content-addressed.
Substitutions from binary caches now require signatures by default. This was already the case on NixOS.
In Linux sandbox builds, we now use /build instead of /tmp as the temporary build directory. This fixes potential security problems when a build accidentally stores its TMPDIR in some security-sensitive place, such as an RPATH.
Pure evaluation mode. This is a variant of the existing restricted evaluation mode. In pure mode, the Nix evaluator forbids access to anything that could cause different evaluations of the same command line arguments to produce a different result. This includes builtin functions such as builtins.getEnv, but more importantly, all filesystem or network access unless a content hash or commit hash is specified. For example, calls to builtins.fetchGit are only allowed if a rev attribute is specified.
The goal of this feature is to enable true reproducibility and traceability of builds (including NixOS system configurations) at the evaluation level. For example, in the future, nixos-rebuild might build configurations from a Nix expression in a Git repository in pure mode. That expression might fetch other repositories such as Nixpkgs via builtins.fetchGit. The commit hash of the top-level repository then uniquely identifies a running system, and, in conjunction with that repository, allows it to be reproduced or modified.
There are several new features to support binary reproducibility (i.e. to help ensure that multiple builds of the same derivation produce exactly the same output). When enforce-determinism is set to false, it’s no longer a fatal error if build rounds produce different output. Also, a hook named diff-hook is provided to allow you to run tools such as diffoscope when build rounds produce different output.
Configuring remote builds is a lot easier now. Provided you are not using the Nix daemon, you can now just specify a remote build machine on the command line, e.g. --option builders 'ssh://my-mac x86_64-darwin'. The environment variable NIX_BUILD_HOOK has been removed and is no longer needed. The environment variable NIX_REMOTE_SYSTEMS is still supported for compatibility, but it is also possible to specify builders in nix.conf by setting the option builders = @.path
If a fixed-output derivation produces a result with an incorrect hash, the output path is moved to the location corresponding to the actual hash and registered as valid. Thus, a subsequent build of the fixed-output derivation with the correct hash is unnecessary.
nix-shell now sets the IN_NIX_SHELL environment variable during evaluation and in the shell itself. This can be used to perform different actions depending on whether you’re in a Nix shell or in a regular build. Nixpkgs provides lib.inNixShell to check this variable during evaluation.
NIX_PATH is now lazy, so URIs in the path are only downloaded if they are needed for evaluation.
You can now use channel: as a short-hand for channel-namehttps://nixos.org/channels/. For example, channel-name/nixexprs.tar.xznix-build channel:nixos-15.09 -A hello will build the GNU Hello package from the nixos-15.09 channel. In the future, this may use Git to fetch updates more efficiently.
When --no-build-output is given, the last 10 lines of the build log will be shown if a build fails.
Networking has been improved:
HTTP/2 is now supported. This makes binary cache lookups much more efficient.
We now retry downloads on many HTTP errors, making binary caches substituters more resilient to temporary failures.
HTTP credentials can now be configured via the standard netrc mechanism.
If S3 support is enabled at compile time, s3:// URIs are supported in all places where Nix allows URIs.
Brotli compression is now supported. In particular, cache.nixos.org build logs are now compressed using Brotli.
nix-env now ignores packages with bad derivation names (in particular those starting with a digit or containing a dot).
Many configuration options have been renamed, either because they were unnecessarily verbose (e.g. build-use-sandbox is now just sandbox) or to reflect generalised behaviour (e.g. binary-caches is now substituters because it allows arbitrary store URIs). The old names are still supported for compatibility.
The max-jobs option can now be set to auto to use the number of CPUs in the system.
Hashes can now be specified in base-64 format, in addition to base-16 and the non-standard base-32.
nix-shell now uses bashInteractive from Nixpkgs, rather than the bash command that happens to be in the caller’s PATH. This is especially important on macOS where the bash provided by the system is seriously outdated and cannot execute stdenv’s setup script.
Nix can now automatically trigger a garbage collection if free disk space drops below a certain level during a build. This is configured using the min-free and max-free options.
nix-store -q --roots and nix-store --gc --print-roots now show temporary and in-memory roots.
Nix can now be extended with plugins. See the documentation of the plugin-files option for more details.
The Nix language has the following new features:
It supports floating point numbers. They are based on the C++ float type and are supported by the existing numerical operators. Export and import to and from JSON and XML works, too.
Derivation attributes can now reference the outputs of the derivation using the placeholder builtin function. For example, the attribute
configureFlags = "--prefix=${placeholder "out"} --includedir=${placeholder "dev"}";
will cause the configureFlags environment variable to contain the actual store paths corresponding to the out and dev outputs.
The following builtin functions are new or extended:
builtins.fetchGit allows Git repositories to be fetched at evaluation time. Thus it differs from the fetchgit function in Nixpkgs, which fetches at build time and cannot be used to fetch Nix expressions during evaluation. A typical use case is to import external NixOS modules from your configuration, e.g.
imports = [ (builtins.fetchGit https://github.com/edolstra/dwarffs + "/module.nix") ];
Similarly, builtins.fetchMercurial allows you to fetch Mercurial repositories.
builtins.path generalises builtins.filterSource and path literals (e.g. ./foo). It allows specifying a store path name that differs from the source path name (e.g. builtins.path { path = ./foo; name = "bar"; }) and also supports filtering out unwanted files.
builtins.fetchurl and builtins.fetchTarball now support sha256 and name attributes.
builtins.split splits a string using a POSIX extended regular expression as the separator.
builtins.partition partitions the elements of a list into two lists, depending on a Boolean predicate.
<nix/fetchurl.nix> now uses the content-addressable tarball cache at http://tarballs.nixos.org/, just like fetchurl in Nixpkgs. (f2682e6e18a76ecbfb8a12c17e3a0ca15c084197)
In restricted and pure evaluation mode, builtin functions that download from the network (such as fetchGit) are permitted to fetch underneath a list of URI prefixes specified in the option allowed-uris.
The Nix build environment has the following changes:
Values such as Booleans, integers, (nested) lists and attribute sets can now be passed to builders in a non-lossy way. If the special attribute __structuredAttrs is set to true, the other derivation attributes are serialised in JSON format and made available to the builder via the file .attrs.json in the builder’s temporary directory. This obviates the need for passAsFile since JSON files have no size restrictions, unlike process environments.
As a convenience to Bash builders, Nix writes a script named .attrs.sh to the builder’s directory that initialises shell variables corresponding to all attributes that are representable in Bash. This includes non-nested (associative) arrays. For example, the attribute hardening.format = true ends up as the Bash associative array element ${hardening[format]}.
Builders can now communicate what build phase they are in by writing messages to the file descriptor specified in NIX_LOG_FD. The current phase is shown by the nix progress indicator.
In Linux sandbox builds, we now provide a default /bin/sh (namely ash from BusyBox).
In structured attribute mode, exportReferencesGraph exports extended information about closures in JSON format. In particular, it includes the sizes and hashes of paths. This is primarily useful for NixOS image builders.
Builds are now killed as soon as Nix receives EOF on the builder’s stdout or stderr. This fixes a bug that allowed builds to hang Nix indefinitely, regardless of timeouts.
The sandbox-paths configuration option can now specify optional paths by appending a ?, e.g. /dev/nvidiactl? will bind-mount /dev/nvidiactl only if it exists.
On Linux, builds are now executed in a user namespace with UID 1000 and GID 100.
A number of significant internal changes were made:
Nix no longer depends on Perl and all Perl components have been rewritten in C++ or removed. The Perl bindings that used to be part of Nix have been moved to a separate package, nix-perl.
All Store classes are now thread-safe. RemoteStore supports multiple concurrent connections to the daemon. This is primarily useful in multi-threaded programs such as hydra-queue-runner.
This release has contributions from Adrien Devresse, Alexander Ried, Alex Cruice, Alexey Shmalko, AmineChikhaoui, Andy Wingo, Aneesh Agrawal, Anthony Cowley, Armijn Hemel, aszlig, Ben Gamari, Benjamin Hipple, Benjamin Staffin, Benno Fünfstück, Bjørn Forsman, Brian McKenna, Charles Strahan, Chase Adams, Chris Martin, Christian Theune, Chris Warburton, Daiderd Jordan, Dan Connolly, Daniel Peebles, Dan Peebles, davidak, David McFarland, Dmitry Kalinkin, Domen Kožar, Eelco Dolstra, Emery Hemingway, Eric Litak, Eric Wolf, Fabian Schmitthenner, Frederik Rietdijk, Gabriel Gonzalez, Giorgio Gallo, Graham Christensen, Guillaume Maudoux, Harmen, Iavael, James Broadhead, James Earl Douglas, Janus Troelsen, Jeremy Shaw, Joachim Schiele, Joe Hermaszewski, Joel Moberg, Johannes 'fish' Ziemke, Jörg Thalheim, Jude Taylor, kballou, Keshav Kini, Kjetil Orbekk, Langston Barrett, Linus Heckemann, Ludovic Courtès, Manav Rathi, Marc Scholten, Markus Hauck, Matt Audesse, Matthew Bauer, Matthias Beyer, Matthieu Coudron, N1X, Nathan Zadoks, Neil Mayhew, Nicolas B. Pierron, Niklas Hambüchen, Nikolay Amiantov, Ole Jørgen Brønner, Orivej Desh, Peter Simons, Peter Stuart, Pyry Jahkola, regnat, Renzo Carbonara, Rhys, Robert Vollmert, Scott Olson, Scott R. Parish, Sergei Trofimovich, Shea Levy, Sheena Artrip, Spencer Baugh, Stefan Junker, Susan Potter, Thomas Tuegel, Timothy Allen, Tristan Hume, Tuomas Tynkkynen, tv, Tyson Whitehead, Vladimír Čunát, Will Dietz, wmertens, Wout Mertens, zimbatm and Zoran Plesivčak.
This release fixes a security bug in Nix’s “build user” build isolation mechanism. Previously, Nix builders had the ability to create setuid binaries owned by a nixbld user. Such a binary could then be used by an attacker to assume a nixbld identity and interfere with subsequent builds running under the same UID.
To prevent this issue, Nix now disallows builders to create setuid and setgid binaries. On Linux, this is done using a seccomp BPF filter. Note that this imposes a small performance penalty (e.g. 1% when building GNU Hello). Using seccomp, we now also prevent the creation of extended attributes and POSIX ACLs since these cannot be represented in the NAR format and (in the case of POSIX ACLs) allow bypassing regular Nix store permissions. On macOS, the restriction is implemented using the existing sandbox mechanism, which now uses a minimal “allow all except the creation of setuid/setgid binaries” profile when regular sandboxing is disabled. On other platforms, the “build user” mechanism is now disabled.
Thanks go to Linus Heckemann for discovering and reporting this bug.
This is primarily a bug fix release. It also has a number of new features:
nix-prefetch-url can now download URLs specified in a Nix expression. For example,
$ nix-prefetch-url -A hello.src
will prefetch the file specified by the fetchurl call in the attribute hello.src from the Nix expression in the current directory, and print the cryptographic hash of the resulting file on stdout. This differs from nix-build -A hello.src in that it doesn't verify the hash, and is thus useful when you’re updating a Nix expression.
You can also prefetch the result of functions that unpack a tarball, such as fetchFromGitHub. For example:
$ nix-prefetch-url --unpack https://github.com/NixOS/patchelf/archive/0.8.tar.gz
or from a Nix expression:
$ nix-prefetch-url -A nix-repl.src
The builtin function <nix/fetchurl.nix> now supports downloading and unpacking NARs. This removes the need to have multiple downloads in the Nixpkgs stdenv bootstrap process (like a separate busybox binary for Linux, or curl/mkdir/sh/bzip2 for Darwin). Now all those files can be combined into a single NAR, optionally compressed using xz.
Nix now supports SHA-512 hashes for verifying fixed-output derivations, and in builtins.hashString.
The new flag --option build-repeat will cause every build to be executed NN+1 times. If the build output differs between any round, the build is rejected, and the output paths are not registered as valid. This is primarily useful to verify build determinism. (We already had a --check option to repeat a previously succeeded build. However, with --check, non-deterministic builds are registered in the DB. Preventing that is useful for Hydra to ensure that non-deterministic builds don't end up getting published to the binary cache.)
The options --check and --option build-repeat , if they detect a difference between two runs of the same derivation and N-K is given, will make the output of the other run available under store-path-check
$ nix-build pkgs/stdenv/linux -A stage1.pkgs.zlib --check -K error: derivation ‘/nix/store/l54i8wlw2265…-zlib-1.2.8.drv’ may not be deterministic: output ‘/nix/store/11a27shh6n2i…-zlib-1.2.8’ differs from ‘/nix/store/11a27shh6n2i…-zlib-1.2.8-check’ $ diffoscope /nix/store/11a27shh6n2i…-zlib-1.2.8 /nix/store/11a27shh6n2i…-zlib-1.2.8-check … ├── lib/libz.a │ ├── metadata │ │ @@ -1,15 +1,15 @@ │ │ -rw-r--r-- 30001/30000 3096 Jan 12 15:20 2016 adler32.o … │ │ +rw-r--r-- 30001/30000 3096 Jan 12 15:28 2016 adler32.o …
Improved FreeBSD support.
nix-env -qa --xml --meta now prints license information.
The maximum number of parallel TCP connections that the binary cache substituter will use has been decreased from 150 to 25. This should prevent upsetting some broken NAT routers, and also improves performance.
All "chroot"-containing strings got renamed to "sandbox". In particular, some Nix options got renamed, but the old names are still accepted as lower-priority aliases.
This release has contributions from Anders Claesson, Anthony Cowley, Bjørn Forsman, Brian McKenna, Danny Wilson, davidak, Eelco Dolstra, Fabian Schmitthenner, FrankHB, Ilya Novoselov, janus, Jim Garrison, John Ericson, Jude Taylor, Ludovic Courtès, Manuel Jacob, Mathnerd314, Pascal Wittmann, Peter Simons, Philip Potter, Preston Bennes, Rommel M. Martinez, Sander van der Burg, Shea Levy, Tim Cuthbertson, Tuomas Tynkkynen, Utku Demir and Vladimír Čunát.
This is primarily a bug fix release. It also has a number of new features:
A number of builtin functions have been added to reduce Nixpkgs/NixOS evaluation time and memory consumption: all, any, concatStringsSep, foldl’, genList, replaceStrings, sort.
The garbage collector is more robust when the disk is full.
Nix supports a new API for building derivations that doesn’t require a .drv file to be present on disk; it only requires an in-memory representation of the derivation. This is used by the Hydra continuous build system to make remote builds more efficient.
The function <nix/fetchurl.nix> now uses a builtin builder (i.e. it doesn’t require starting an external process; the download is performed by Nix itself). This ensures that derivation paths don’t change when Nix is upgraded, and obviates the need for ugly hacks to support chroot execution.
--version -v now prints some configuration information, in particular what compile-time optional features are enabled, and the paths of various directories.
Build users have their supplementary groups set correctly.
This release has contributions from Eelco Dolstra, Guillaume Maudoux, Iwan Aucamp, Jaka Hudoklin, Kirill Elagin, Ludovic Courtès, Manolis Ragkousis, Nicolas B. Pierron and Shea Levy.
In addition to the usual bug fixes, this release has the following new features:
Signed binary cache support. You can enable signature checking by adding the following to nix.conf:
signed-binary-caches = * binary-cache-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
This will prevent Nix from downloading any binary from the cache that is not signed by one of the keys listed in binary-cache-public-keys.
Signature checking is only supported if you built Nix with the libsodium package.
Note that while Nix has had experimental support for signed binary caches since version 1.7, this release changes the signature format in a backwards-incompatible way.
Automatic downloading of Nix expression tarballs. In various places, you can now specify the URL of a tarball containing Nix expressions (such as Nixpkgs), which will be downloaded and unpacked automatically. For example:
In nix-env:
$ nix-env -f https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz -iA firefox
This installs Firefox from the latest tested and built revision of the NixOS 14.12 channel.
In nix-build and nix-shell:
$ nix-build https://github.com/NixOS/nixpkgs/archive/master.tar.gz -A hello
This builds GNU Hello from the latest revision of the Nixpkgs master branch.
In the Nix search path (as specified via NIX_PATH or -I). For example, to start a shell containing the Pan package from a specific version of Nixpkgs:
$ nix-shell -p pan -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/8a3eea054838b55aca962c3fbde9c83c102b8bf2.tar.gz
In nixos-rebuild (on NixOS):
$ nixos-rebuild test -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-unstable.tar.gz
In Nix expressions, via the new builtin function fetchTarball:
with import (fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz) {}; …
(This is not allowed in restricted mode.)
nix-shell improvements:
nix-shell now has a flag --run to execute a command in the nix-shell environment, e.g. nix-shell --run make. This is like the existing --command flag, except that it uses a non-interactive shell (ensuring that hitting Ctrl-C won’t drop you into the child shell).
nix-shell can now be used as a #!-interpreter. This allows you to write scripts that dynamically fetch their own dependencies. For example, here is a Haskell script that, when invoked, first downloads GHC and the Haskell packages on which it depends:
#! /usr/bin/env nix-shell #! nix-shell -i runghc -p haskellPackages.ghc haskellPackages.HTTP import Network.HTTP main = do resp <- Network.HTTP.simpleHTTP (getRequest "http://nixos.org/") body <- getResponseBody resp print (take 100 body)
Of course, the dependencies are cached in the Nix store, so the second invocation of this script will be much faster.
Chroot improvements:
Chroot builds are now supported on Mac OS X (using its sandbox mechanism).
If chroots are enabled, they are now used for all derivations, including fixed-output derivations (such as fetchurl). The latter do have network access, but can no longer access the host filesystem. If you need the old behaviour, you can set the option build-use-chroot to relaxed.
On Linux, if chroots are enabled, builds are performed in a private PID namespace once again. (This functionality was lost in Nix 1.8.)
Store paths listed in build-chroot-dirs are now automatically expanded to their closure. For instance, if you want /nix/store/…-bash/bin/sh mounted in your chroot as /bin/sh, you only need to say build-chroot-dirs = /bin/sh=/nix/store/…-bash/bin/sh; it is no longer necessary to specify the dependencies of Bash.
The new derivation attribute passAsFile allows you to specify that the contents of derivation attributes should be passed via files rather than environment variables. This is useful if you need to pass very long strings that exceed the size limit of the environment. The Nixpkgs function writeTextFile uses this.
You can now use ~ in Nix file names to refer to your home directory, e.g. import ~/.nixpkgs/config.nix.
Nix has a new option restrict-eval that allows limiting what paths the Nix evaluator has access to. By passing --option restrict-eval true to Nix, the evaluator will throw an exception if an attempt is made to access any file outside of the Nix search path. This is primarily intended for Hydra to ensure that a Hydra jobset only refers to its declared inputs (and is therefore reproducible).
nix-env now only creates a new “generation” symlink in /nix/var/nix/profiles if something actually changed.
The environment variable NIX_PAGER can now be set to override PAGER. You can set it to cat to disable paging for Nix commands only.
Failing <...> lookups now show position information.
Improved Boehm GC use: we disabled scanning for interior pointers, which should reduce the “Repeated allocation of very large block” warnings and associated retention of memory.
This release has contributions from aszlig, Benjamin Staffin, Charles Strahan, Christian Theune, Daniel Hahler, Danylo Hlynskyi Daniel Peebles, Dan Peebles, Domen Kožar, Eelco Dolstra, Harald van Dijk, Hoang Xuan Phu, Jaka Hudoklin, Jeff Ramnani, j-keck, Linquize, Luca Bruno, Michael Merickel, Oliver Dunkl, Rob Vermaas, Rok Garbas, Shea Levy, Tobias Geerinckx-Rice and William A. Kennington III.
Breaking change: to address a race condition, the remote build hook mechanism now uses nix-store --serve on the remote machine. This requires build slaves to be updated to Nix 1.8.
Nix now uses HTTPS instead of HTTP to access the default binary cache, cache.nixos.org.
nix-env selectors are now regular expressions. For instance, you can do
$ nix-env -qa '.*zip.*'
to query all packages with a name containing zip.
nix-store --read-log can now fetch remote build logs. If a build log is not available locally, then ‘nix-store -l’ will now try to download it from the servers listed in the ‘log-servers’ option in nix.conf. For instance, if you have the configuration option
log-servers = http://hydra.nixos.org/log
then it will try to get logs from http://hydra.nixos.org/log/. This allows you to do things like: base name of the store path
$ nix-store -l $(which xterm)
and get a log even if xterm wasn't built locally.
New builtin functions: attrValues, deepSeq, fromJSON, readDir, seq.
nix-instantiate --eval now has a --json flag to print the resulting value in JSON format.
nix-copy-closure now uses nix-store --serve on the remote side to send or receive closures. This fixes a race condition between nix-copy-closure and the garbage collector.
Derivations can specify the new special attribute allowedRequisites, which has a similar meaning to allowedReferences. But instead of only enforcing to explicitly specify the immediate references, it requires the derivation to specify all the dependencies recursively (hence the name, requisites) that are used by the resulting output.
On Mac OS X, Nix now handles case collisions when importing closures from case-sensitive file systems. This is mostly useful for running NixOps on Mac OS X.
The Nix daemon has new configuration options allowed-users (specifying the users and groups that are allowed to connect to the daemon) and trusted-users (specifying the users and groups that can perform privileged operations like specifying untrusted binary caches).
The configuration option build-cores now defaults to the number of available CPU cores.
Build users are now used by default when Nix is invoked as root. This prevents builds from accidentally running as root.
Nix now includes systemd units and Upstart jobs.
Speed improvements to nix-store --optimise.
Language change: the == operator now ignores string contexts (the “dependencies” of a string).
Nix now filters out Nix-specific ANSI escape sequences on standard error. They are supposed to be invisible, but some terminals show them anyway.
Various commands now automatically pipe their output into the pager as specified by the PAGER environment variable.
Several improvements to reduce memory consumption in the evaluator.
This release has contributions from Adam Szkoda, Aristid Breitkreuz, Bob van der Linden, Charles Strahan, darealshinji, Eelco Dolstra, Gergely Risko, Joel Taylor, Ludovic Courtès, Marko Durkovic, Mikey Ariel, Paul Colomiets, Ricardo M. Correia, Ricky Elrod, Robert Helgesson, Rob Vermaas, Russell O'Connor, Shea Levy, Shell Turner, Sönke Hahn, Steve Purcell, Vladimír Čunát and Wout Mertens.
In addition to the usual bug fixes, this release has the following new features:
Antiquotation is now allowed inside of quoted attribute names (e.g. set."${foo}"). In the case where the attribute name is just a single antiquotation, the quotes can be dropped (e.g. the above example can be written set.${foo}). If an attribute name inside of a set declaration evaluates to null (e.g. { ${null} = false; }), then that attribute is not added to the set.
Experimental support for cryptographically signed binary caches. See the commit for details.
An experimental new substituter, download-via-ssh, that fetches binaries from remote machines via SSH. Specifying the flags --option use-ssh-substituter true --option ssh-substituter-hosts will cause Nix to download binaries from the specified machine, if it has them.user@hostname
nix-store -r and nix-build have a new flag, --check, that builds a previously built derivation again, and prints an error message if the output is not exactly the same. This helps to verify whether a derivation is truly deterministic. For example:
$ nix-build '<nixpkgs>' -A patchelf…$ nix-build '<nixpkgs>' -A patchelf --check…error: derivation `/nix/store/1ipvxs…-patchelf-0.6' may not be deterministic: hash mismatch in output `/nix/store/4pc1dm…-patchelf-0.6.drv'
The nix-instantiate flags --eval-only and --parse-only have been renamed to --eval and --parse, respectively.
nix-instantiate, nix-build and nix-shell now have a flag --expr (or -E) that allows you to specify the expression to be evaluated as a command line argument. For instance, nix-instantiate --eval -E '1 + 2' will print 3.
nix-shell improvements:
It has a new flag, --packages (or -p), that sets up a build environment containing the specified packages from Nixpkgs. For example, the command
$ nix-shell -p sqlite xorg.libX11 hello
will start a shell in which the given packages are present.
It now uses shell.nix as the default expression, falling back to default.nix if the former doesn’t exist. This makes it convenient to have a shell.nix in your project to set up a nice development environment.
It evaluates the derivation attribute shellHook, if set. Since stdenv does not normally execute this hook, it allows you to do nix-shell-specific setup.
It preserves the user’s timezone setting.
In chroots, Nix now sets up a /dev containing only a minimal set of devices (such as /dev/null). Note that it only does this if you don’t have /dev listed in your build-chroot-dirs setting; otherwise, it will bind-mount the /dev from outside the chroot.
Similarly, if you don’t have /dev/pts listed in build-chroot-dirs, Nix will mount a private devpts filesystem on the chroot’s /dev/pts.
New built-in function: builtins.toJSON, which returns a JSON representation of a value.
nix-env -q has a new flag --json to print a JSON representation of the installed or available packages.
nix-env now supports meta attributes with more complex values, such as attribute sets.
The -A flag now allows attribute names with dots in them, e.g.
$ nix-instantiate --eval '<nixos>' -A 'config.systemd.units."nscd.service".text'
The --max-freed option to nix-store --gc now accepts a unit specifier. For example, nix-store --gc --max-freed 1G will free up to 1 gigabyte of disk space.
nix-collect-garbage has a new flag --delete-older-than Nd, which deletes all user environment generations older than N days. Likewise, nix-env --delete-generations accepts a Nd age limit.
Nix now heuristically detects whether a build failure was due to a disk-full condition. In that case, the build is not flagged as “permanently failed”. This is mostly useful for Hydra, which needs to distinguish between permanent and transient build failures.
There is a new symbol __curPos that expands to an attribute set containing its file name and line and column numbers, e.g. { file = "foo.nix"; line = 10; column = 5; }. There also is a new builtin function, unsafeGetAttrPos, that returns the position of an attribute. This is used by Nixpkgs to provide location information in error messages, e.g.
$ nix-build '<nixpkgs>' -A libreoffice --argstr system x86_64-darwin error: the package ‘libreoffice-4.0.5.2’ in ‘.../applications/office/libreoffice/default.nix:263’ is not supported on ‘x86_64-darwin’
The garbage collector is now more concurrent with other Nix processes because it releases certain locks earlier.
The binary tarball installer has been improved. You can now install Nix by running:
$ bash <(curl https://nixos.org/nix/install)
More evaluation errors include position information. For instance, selecting a missing attribute will print something like
error: attribute `nixUnstabl' missing, at /etc/nixos/configurations/misc/eelco/mandark.nix:216:15
The command nix-setuid-helper is gone.
Nix no longer uses Automake, but instead has a non-recursive, GNU Make-based build system.
All installed libraries now have the prefix libnix. In particular, this gets rid of libutil, which could clash with libraries with the same name from other packages.
Nix now requires a compiler that supports C++11.
This release has contributions from Danny Wilson, Domen Kožar, Eelco Dolstra, Ian-Woo Kim, Ludovic Courtès, Maxim Ivanov, Petr Rockai, Ricardo M. Correia and Shea Levy.
This is primarily a bug fix release. Changes of interest are:
Nix 1.6 accidentally changed the semantics of antiquoted paths in strings, such as "${/foo}/bar". This release reverts to the Nix 1.5.3 behaviour.
Previously, Nix optimised expressions such as "${ to expr}"expr. Thus it neither checked whether expr could be coerced to a string, nor applied such coercions. This meant that "${123}" evaluatued to 123, and "${./foo}" evaluated to ./foo (even though "${./foo} " evaluates to "/nix/store/). Nix now checks the type of antiquoted expressions and applies coercions.hash-foo "
Nix now shows the exact position of undefined variables. In particular, undefined variable errors in a with previously didn't show any position information, so this makes it a lot easier to fix such errors.
Undefined variables are now treated consistently. Previously, the tryEval function would catch undefined variables inside a with but not outside. Now tryEval never catches undefined variables.
Bash completion in nix-shell now works correctly.
Stack traces are less verbose: they no longer show calls to builtin functions and only show a single line for each derivation on the call stack.
New built-in function: builtins.typeOf, which returns the type of its argument as a string.
In addition to the usual bug fixes, this release has several new features:
The command nix-build --run-env has been renamed to nix-shell.
nix-shell now sources $stdenv/setup inside the interactive shell, rather than in a parent shell. This ensures that shell functions defined by stdenv can be used in the interactive shell.
nix-shell has a new flag --pure to clear the environment, so you get an environment that more closely corresponds to the “real” Nix build.
nix-shell now sets the shell prompt (PS1) to ensure that Nix shells are distinguishable from your regular shells.
nix-env no longer requires a * argument to match all packages, so nix-env -qa is equivalent to nix-env -qa '*'.
nix-env -i has a new flag --remove-all (-r) to remove all previous packages from the profile. This makes it easier to do declarative package management similar to NixOS’s environment.systemPackages. For instance, if you have a specification my-packages.nix like this:
with import <nixpkgs> {};
[ thunderbird
geeqie
...
]
then after any change to this file, you can run:
$ nix-env -f my-packages.nix -ir
to update your profile to match the specification.
The ‘with’ language construct is now more lazy. It only evaluates its argument if a variable might actually refer to an attribute in the argument. For instance, this now works:
let
pkgs = with pkgs; { foo = "old"; bar = foo; } // overrides;
overrides = { foo = "new"; };
in pkgs.bar
This evaluates to "new", while previously it gave an “infinite recursion” error.
Nix now has proper integer arithmetic operators. For instance, you can write x + y instead of builtins.add x y, or x < y instead of builtins.lessThan x y. The comparison operators also work on strings.
On 64-bit systems, Nix integers are now 64 bits rather than 32 bits.
When using the Nix daemon, the nix-daemon worker process now runs on the same CPU as the client, on systems that support setting CPU affinity. This gives a significant speedup on some systems.
If a stack overflow occurs in the Nix evaluator, you now get a proper error message (rather than “Segmentation fault”) on some systems.
In addition to directories, you can now bind-mount regular files in chroots through the (now misnamed) option build-chroot-dirs.
This release has contributions from Domen Kožar, Eelco Dolstra, Florian Friesdorf, Gergely Risko, Ivan Kozik, Ludovic Courtès and Shea Levy.
This is primarily a bug fix release. It has contributions from Eelco Dolstra, Lluís Batlle i Rossell and Shea Levy.
This is a brown paper bag release to fix a regression introduced by the hard link security fix in 1.4.
This release fixes a security bug in multi-user operation. It was possible for derivations to cause the mode of files outside of the Nix store to be changed to 444 (read-only but world-readable) by creating hard links to those files (details).
There are also the following improvements:
New built-in function: builtins.hashString.
Build logs are now stored in /nix/var/log/nix/drvs/, where XX/XX is the first two characters of the derivation. This is useful on machines that keep a lot of build logs (such as Hydra servers).
The function corepkgs/fetchurl can now make the downloaded file executable. This will allow getting rid of all bootstrap binaries in the Nixpkgs source tree.
Language change: The expression "${./path} ..." now evaluates to a string instead of a path.
This is primarily a bug fix release. When this version is first run on Linux, it removes any immutable bits from the Nix store and increases the schema version of the Nix store. (The previous release removed support for setting the immutable bit; this release clears any remaining immutable bits to make certain operations more efficient.)
This release has contributions from Eelco Dolstra and Stuart Pernsteiner.
This release has the following improvements and changes:
Nix has a new binary substituter mechanism: the binary cache. A binary cache contains pre-built binaries of Nix packages. Whenever Nix wants to build a missing Nix store path, it will check a set of binary caches to see if any of them has a pre-built binary of that path. The configuration setting binary-caches contains a list of URLs of binary caches. For instance, doing
$ nix-env -i thunderbird --option binary-caches http://cache.nixos.org
will install Thunderbird and its dependencies, using the available pre-built binaries in http://cache.nixos.org. The main advantage over the old “manifest”-based method of getting pre-built binaries is that you don’t have to worry about your manifest being in sync with the Nix expressions you’re installing from; i.e., you don’t need to run nix-pull to update your manifest. It’s also more scalable because you don’t need to redownload a giant manifest file every time.
A Nix channel can provide a binary cache URL that will be used automatically if you subscribe to that channel. If you use the Nixpkgs or NixOS channels (http://nixos.org/channels) you automatically get the cache http://cache.nixos.org.
Binary caches are created using nix-push. For details on the operation and format of binary caches, see the nix-push manpage. More details are provided in this nix-dev posting.
Multiple output support should now be usable. A derivation can declare that it wants to produce multiple store paths by saying something like
outputs = [ "lib" "headers" "doc" ];
This will cause Nix to pass the intended store path of each output to the builder through the environment variables lib, headers and doc. Other packages can refer to a specific output by referring to pkg.output
buildInputs = [ pkg.lib pkg.headers ];
If you install a package with multiple outputs using nix-env, each output path will be symlinked into the user environment.
Dashes are now valid as part of identifiers and attribute names.
The new operation nix-store --repair-path allows corrupted or missing store paths to be repaired by redownloading them. nix-store --verify --check-contents --repair will scan and repair all paths in the Nix store. Similarly, nix-env, nix-build, nix-instantiate and nix-store --realise have a --repair flag to detect and fix bad paths by rebuilding or redownloading them.
Nix no longer sets the immutable bit on files in the Nix store. Instead, the recommended way to guard the Nix store against accidental modification on Linux is to make it a read-only bind mount, like this:
$ mount --bind /nix/store /nix/store $ mount -o remount,ro,bind /nix/store
Nix will automatically make /nix/store writable as needed (using a private mount namespace) to allow modifications.
Store optimisation (replacing identical files in the store with hard links) can now be done automatically every time a path is added to the store. This is enabled by setting the configuration option auto-optimise-store to true (disabled by default).
Nix now supports xz compression for NARs in addition to bzip2. It compresses about 30% better on typical archives and decompresses about twice as fast.
Basic Nix expression evaluation profiling: setting the environment variable NIX_COUNT_CALLS to 1 will cause Nix to print how many times each primop or function was executed.
New primops: concatLists, elem, elemAt and filter.
The command nix-copy-closure has a new flag --use-substitutes (-s) to download missing paths on the target machine using the substitute mechanism.
The command nix-worker has been renamed to nix-daemon. Support for running the Nix worker in “slave” mode has been removed.
The --help flag of every Nix command now invokes man.
Chroot builds are now supported on systemd machines.
This release has contributions from Eelco Dolstra, Florian Friesdorf, Mats Erik Andersson and Shea Levy.
This release has the following improvements:
On Linux, when doing a chroot build, Nix now uses various namespace features provided by the Linux kernel to improve build isolation. Namely:
The private network namespace ensures that builders cannot talk to the outside world (or vice versa): each build only sees a private loopback interface. This also means that two concurrent builds can listen on the same port (e.g. as part of a test) without conflicting with each other.
The PID namespace causes each build to start as PID 1. Processes outside of the chroot are not visible to those on the inside. On the other hand, processes inside the chroot are visible from the outside (though with different PIDs).
The IPC namespace prevents the builder from communicating with outside processes using SysV IPC mechanisms (shared memory, message queues, semaphores). It also ensures that all IPC objects are destroyed when the builder exits.
The UTS namespace ensures that builders see a hostname of localhost rather than the actual hostname.
The private mount namespace was already used by Nix to ensure that the bind-mounts used to set up the chroot are cleaned up automatically.
Build logs are now compressed using bzip2. The command nix-store -l decompresses them on the fly. This can be disabled by setting the option build-compress-log to false.
The creation of build logs in /nix/var/log/nix/drvs can be disabled by setting the new option build-keep-log to false. This is useful, for instance, for Hydra build machines.
Nix now reserves some space in /nix/var/nix/db/reserved to ensure that the garbage collector can run successfully if the disk is full. This is necessary because SQLite transactions fail if the disk is full.
Added a basic fetchurl function. This is not intended to replace the fetchurl in Nixpkgs, but is useful for bootstrapping; e.g., it will allow us to get rid of the bootstrap binaries in the Nixpkgs source tree and download them instead. You can use it by doing import <nix/fetchurl.nix> { url = . (Shea Levy)url; sha256 = "hash"; }
Improved RPM spec file. (Michel Alexandre Salim)
Support for on-demand socket-based activation in the Nix daemon with systemd.
Added a manpage for nix.conf(5).
When using the Nix daemon, the -s flag in nix-env -qa is now much faster.
There have been numerous improvements and bug fixes since the previous release. Here are the most significant:
Nix can now optionally use the Boehm garbage collector. This significantly reduces the Nix evaluator’s memory footprint, especially when evaluating large NixOS system configurations. It can be enabled using the --enable-gc configure option.
Nix now uses SQLite for its database. This is faster and more flexible than the old ad hoc format. SQLite is also used to cache the manifests in /nix/var/nix/manifests, resulting in a significant speedup.
Nix now has an search path for expressions. The search path is set using the environment variable NIX_PATH and the -I command line option. In Nix expressions, paths between angle brackets are used to specify files that must be looked up in the search path. For instance, the expression <nixpkgs/default.nix> looks for a file nixpkgs/default.nix relative to every element in the search path.
The new command nix-build --run-env builds all dependencies of a derivation, then starts a shell in an environment containing all variables from the derivation. This is useful for reproducing the environment of a derivation for development.
The new command nix-store --verify-path verifies that the contents of a store path have not changed.
The new command nix-store --print-env prints out the environment of a derivation in a format that can be evaluated by a shell.
Attribute names can now be arbitrary strings. For instance, you can write { "foo-1.2" = …; "bla bla" = …; }."bla bla".
Attribute selection can now provide a default value using the or operator. For instance, the expression x.y.z or e evaluates to the attribute x.y.z if it exists, and e otherwise.
The right-hand side of the ? operator can now be an attribute path, e.g., attrs ? a.b.c.
On Linux, Nix will now make files in the Nix store immutable on filesystems that support it. This prevents accidental modification of files in the store by the root user.
Nix has preliminary support for derivations with multiple outputs. This is useful because it allows parts of a package to be deployed and garbage-collected separately. For instance, development parts of a package such as header files or static libraries would typically not be part of the closure of an application, resulting in reduced disk usage and installation time.
The Nix store garbage collector is faster and holds the global lock for a shorter amount of time.
The option --timeout (corresponding to the configuration setting build-timeout) allows you to set an absolute timeout on builds — if a build runs for more than the given number of seconds, it is terminated. This is useful for recovering automatically from builds that are stuck in an infinite loop but keep producing output, and for which --max-silent-time is ineffective.
Nix development has moved to GitHub (https://github.com/NixOS/nix).
This release has the following improvements:
The Nix expression evaluator is now much faster in most cases: typically, 3 to 8 times compared to the old implementation. It also uses less memory. It no longer depends on the ATerm library.
Support for configurable parallelism inside builders. Build scripts have always had the ability to perform multiple build actions in parallel (for instance, by running make -j 2), but this was not desirable because the number of actions to be performed in parallel was not configurable. Nix now has an option --cores as well as a configuration setting Nbuild-cores = that causes the environment variable NNIX_BUILD_CORES to be set to N when the builder is invoked. The builder can use this at its discretion to perform a parallel build, e.g., by calling make -j N. In Nixpkgs, this can be enabled on a per-package basis by setting the derivation attribute enableParallelBuilding to true.
nix-store -q now supports XML output through the --xml flag.
Several bug fixes.
This is a bug-fix release. Among other things, it fixes building on Mac OS X (Snow Leopard), and improves the contents of /etc/passwd and /etc/group in chroot builds.
This release has the following improvements:
The garbage collector now starts deleting garbage much faster than before. It no longer determines liveness of all paths in the store, but does so on demand.
Added a new operation, nix-store --query --roots, that shows the garbage collector roots that directly or indirectly point to the given store paths.
Removed support for converting Berkeley DB-based Nix databases to the new schema.
Removed the --use-atime and --max-atime garbage collector options. They were not very useful in practice.
On Windows, Nix now requires Cygwin 1.7.x.
A few bug fixes.
This is primarily a bug fix release. It has some new features:
Syntactic sugar for writing nested attribute sets. Instead of
{
foo = {
bar = 123;
xyzzy = true;
};
a = { b = { c = "d"; }; };
}
you can write
{
foo.bar = 123;
foo.xyzzy = true;
a.b.c = "d";
}
This is useful, for instance, in NixOS configuration files.
Support for Nix channels generated by Hydra, the Nix-based continuous build system. (Hydra generates NAR archives on the fly, so the size and hash of these archives isn’t known in advance.)
Support i686-linux builds directly on x86_64-linux Nix installations. This is implemented using the personality() syscall, which causes uname to return i686 in child processes.
Various improvements to the chroot support. Building in a chroot works quite well now.
Nix no longer blocks if it tries to build a path and another process is already building the same path. Instead it tries to build another buildable path first. This improves parallelism.
Support for large (> 4 GiB) files in NAR archives.
Various (performance) improvements to the remote build mechanism.
New primops: builtins.addErrorContext (to add a string to stack traces — useful for debugging), builtins.isBool, builtins.isString, builtins.isInt, builtins.intersectAttrs.
OpenSolaris support (Sander van der Burg).
Stack traces are no longer displayed unless the --show-trace option is used.
The scoping rules for inherit ( in recursive attribute sets have changed. The expression e) ...e can now refer to the attributes defined in the containing set.
Nix no longer uses Berkeley DB to store Nix store metadata. The principal advantages of the new storage scheme are: it works properly over decent implementations of NFS (allowing Nix stores to be shared between multiple machines); no recovery is needed when a Nix process crashes; no write access is needed for read-only operations; no more running out of Berkeley DB locks on certain operations.
You still need to compile Nix with Berkeley DB support if you want Nix to automatically convert your old Nix store to the new schema. If you don’t need this, you can build Nix with the configure option --disable-old-db-compat.
After the automatic conversion to the new schema, you can delete the old Berkeley DB files:
$ cd /nix/var/nix/db $ rm __db* log.* derivers references referrers reserved validpaths DB_CONFIG
The new metadata is stored in the directories /nix/var/nix/db/info and /nix/var/nix/db/referrer. Though the metadata is stored in human-readable plain-text files, they are not intended to be human-editable, as Nix is rather strict about the format.
The new storage schema may or may not require less disk space than the Berkeley DB environment, mostly depending on the cluster size of your file system. With 1 KiB clusters (which seems to be the ext3 default nowadays) it usually takes up much less space.
There is a new substituter that copies paths directly from other (remote) Nix stores mounted somewhere in the filesystem. For instance, you can speed up an installation by mounting some remote Nix store that already has the packages in question via NFS or sshfs. The environment variable NIX_OTHER_STORES specifies the locations of the remote Nix directories, e.g. /mnt/remote-fs/nix.
New nix-store operations --dump-db and --load-db to dump and reload the Nix database.
The garbage collector has a number of new options to allow only some of the garbage to be deleted. The option --max-freed tells the collector to stop after at least NN bytes have been deleted. The option --max-links tells it to stop after the link count on N/nix/store has dropped below N. This is useful for very large Nix stores on filesystems with a 32000 subdirectories limit (like ext3). The option --use-atime causes store paths to be deleted in order of ascending last access time. This allows non-recently used stuff to be deleted. The option --max-atime specifies an upper limit to the last accessed time of paths that may be deleted. For instance, time
$ nix-store --gc -v --max-atime $(date +%s -d "2 months ago")
deletes everything that hasn’t been accessed in two months.
nix-env now uses optimistic profile locking when performing an operation like installing or upgrading, instead of setting an exclusive lock on the profile. This allows multiple nix-env -i / -u / -e operations on the same profile in parallel. If a nix-env operation sees at the end that the profile was changed in the meantime by another process, it will just restart. This is generally cheap because the build results are still in the Nix store.
The option --dry-run is now supported by nix-store -r and nix-build.
The information previously shown by --dry-run (i.e., which derivations will be built and which paths will be substituted) is now always shown by nix-env, nix-store -r and nix-build. The total download size of substitutable paths is now also shown. For instance, a build will show something like
the following derivations will be built: /nix/store/129sbxnk5n466zg6r1qmq1xjv9zymyy7-activate-configuration.sh.drv /nix/store/7mzy971rdm8l566ch8hgxaf89x7lr7ik-upstart-jobs.drv ... the following paths will be downloaded/copied (30.02 MiB): /nix/store/4m8pvgy2dcjgppf5b4cj5l6wyshjhalj-samba-3.2.4 /nix/store/7h1kwcj29ip8vk26rhmx6bfjraxp0g4l-libunwind-0.98.6 ...
Language features:
@-patterns as in Haskell. For instance, in a function definition
f = args @ {x, y, z}: ...; args refers to the argument as a whole, which is further pattern-matched against the attribute set pattern {x, y, z}.
“...” (ellipsis) patterns. An attribute set pattern can now say ... at the end of the attribute name list to specify that the function takes at least the listed attributes, while ignoring additional attributes. For instance,
{stdenv, fetchurl, fuse, ...}: ...defines a function that accepts any attribute set that includes at least the three listed attributes.
New primops: builtins.parseDrvName (split a package name string like "nix-0.12pre12876" into its name and version components, e.g. "nix" and "0.12pre12876"), builtins.compareVersions (compare two version strings using the same algorithm that nix-env uses), builtins.length (efficiently compute the length of a list), builtins.mul (integer multiplication), builtins.div (integer division).
nix-prefetch-url now supports mirror:// URLs, provided that the environment variable NIXPKGS_ALL points at a Nixpkgs tree.
Removed the commands nix-pack-closure and nix-unpack-closure. You can do almost the same thing but much more efficiently by doing nix-store --export $(nix-store -qR and paths) > closurenix-store --import < closure.
Lots of bug fixes, including a big performance bug in the handling of with-expressions.
Nix 0.11 has many improvements over the previous stable release. The most important improvement is secure multi-user support. It also features many usability enhancements and language extensions, many of them prompted by NixOS, the purely functional Linux distribution based on Nix. Here is an (incomplete) list:
Secure multi-user support. A single Nix store can now be shared between multiple (possible untrusted) users. This is an important feature for NixOS, where it allows non-root users to install software. The old setuid method for sharing a store between multiple users has been removed. Details for setting up a multi-user store can be found in the manual.
The new command nix-copy-closure gives you an easy and efficient way to exchange software between machines. It copies the missing parts of the closure of a set of store path to or from a remote machine via ssh.
A new kind of string literal: strings between double single-quotes ('') have indentation “intelligently” removed. This allows large strings (such as shell scripts or configuration file fragments in NixOS) to cleanly follow the indentation of the surrounding expression. It also requires much less escaping, since '' is less common in most languages than ".
nix-env --set modifies the current generation of a profile so that it contains exactly the specified derivation, and nothing else. For example, nix-env -p /nix/var/nix/profiles/browser --set firefox lets the profile named browser contain just Firefox.
nix-env now maintains meta-information about installed packages in profiles. The meta-information is the contents of the meta attribute of derivations, such as description or homepage. The command nix-env -q --xml --meta shows all meta-information.
nix-env now uses the meta.priority attribute of derivations to resolve filename collisions between packages. Lower priority values denote a higher priority. For instance, the GCC wrapper package and the Binutils package in Nixpkgs both have a file bin/ld, so previously if you tried to install both you would get a collision. Now, on the other hand, the GCC wrapper declares a higher priority than Binutils, so the former’s bin/ld is symlinked in the user environment.
nix-env -i / -u: instead of breaking package ties by version, break them by priority and version number. That is, if there are multiple packages with the same name, then pick the package with the highest priority, and only use the version if there are multiple packages with the same priority.
This makes it possible to mark specific versions/variant in Nixpkgs more or less desirable than others. A typical example would be a beta version of some package (e.g., gcc-4.2.0rc1) which should not be installed even though it is the highest version, except when it is explicitly selected (e.g., nix-env -i gcc-4.2.0rc1).
nix-env --set-flag allows meta attributes of installed packages to be modified. There are several attributes that can be usefully modified, because they affect the behaviour of nix-env or the user environment build script:
meta.priority can be changed to resolve filename clashes (see above).
meta.keep can be set to true to prevent the package from being upgraded or replaced. Useful if you want to hang on to an older version of a package.
meta.active can be set to false to “disable” the package. That is, no symlinks will be generated to the files of the package, but it remains part of the profile (so it won’t be garbage-collected). Set it back to true to re-enable the package.
nix-env -q now has a flag --prebuilt-only (-b) that causes nix-env to show only those derivations whose output is already in the Nix store or that can be substituted (i.e., downloaded from somewhere). In other words, it shows the packages that can be installed “quickly”, i.e., don’t need to be built from source. The -b flag is also available in nix-env -i and nix-env -u to filter out derivations for which no pre-built binary is available.
The new option --argstr (in nix-env, nix-instantiate and nix-build) is like --arg, except that the value is a string. For example, --argstr system i686-linux is equivalent to --arg system \"i686-linux\" (note that --argstr prevents annoying quoting around shell arguments).
nix-store has a new operation --read-log (-l) paths that shows the build log of the given paths.
Nix now uses Berkeley DB 4.5. The database is upgraded automatically, but you should be careful not to use old versions of Nix that still use Berkeley DB 4.4.
The option --max-silent-time (corresponding to the configuration setting build-max-silent-time) allows you to set a timeout on builds — if a build produces no output on stdout or stderr for the given number of seconds, it is terminated. This is useful for recovering automatically from builds that are stuck in an infinite loop.
nix-channel: each subscribed channel is its own attribute in the top-level expression generated for the channel. This allows disambiguation (e.g. nix-env -i -A nixpkgs_unstable.firefox).
The substitutes table has been removed from the database. This makes operations such as nix-pull and nix-channel --update much, much faster.
nix-pull now supports bzip2-compressed manifests. This speeds up channels.
nix-prefetch-url now has a limited form of caching. This is used by nix-channel to prevent unnecessary downloads when the channel hasn’t changed.
nix-prefetch-url now by default computes the SHA-256 hash of the file instead of the MD5 hash. In calls to fetchurl you should pass the sha256 attribute instead of md5. You can pass either a hexadecimal or a base-32 encoding of the hash.
Nix can now perform builds in an automatically generated “chroot”. This prevents a builder from accessing stuff outside of the Nix store, and thus helps ensure purity. This is an experimental feature.
The new command nix-store --optimise reduces Nix store disk space usage by finding identical files in the store and hard-linking them to each other. It typically reduces the size of the store by something like 25-35%.
~/.nix-defexpr can now be a directory, in which case the Nix expressions in that directory are combined into an attribute set, with the file names used as the names of the attributes. The command nix-env --import (which set the ~/.nix-defexpr symlink) is removed.
Derivations can specify the new special attribute allowedReferences to enforce that the references in the output of a derivation are a subset of a declared set of paths. For example, if allowedReferences is an empty list, then the output must not have any references. This is used in NixOS to check that generated files such as initial ramdisks for booting Linux don’t have any dependencies.
The new attribute exportReferencesGraph allows builders access to the references graph of their inputs. This is used in NixOS for tasks such as generating ISO-9660 images that contain a Nix store populated with the closure of certain paths.
Fixed-output derivations (like fetchurl) can define the attribute impureEnvVars to allow external environment variables to be passed to builders. This is used in Nixpkgs to support proxy configuration, among other things.
Several new built-in functions: builtins.attrNames, builtins.filterSource, builtins.isAttrs, builtins.isFunction, builtins.listToAttrs, builtins.stringLength, builtins.sub, builtins.substring, throw, builtins.trace, builtins.readFile.
This release fixes two somewhat obscure bugs that occur when evaluating Nix expressions that are stored inside the Nix store (NIX-67). These do not affect most users.
This version of Nix uses Berkeley DB 4.4 instead of 4.3. The database is upgraded automatically, but you should be careful not to use old versions of Nix that still use Berkeley DB 4.3. In particular, if you use a Nix installed through Nix, you should run
$ nix-store --clear-substitutes
first.
nix-env usability improvements:
An option --compare-versions (or -c) has been added to nix-env --query to allow you to compare installed versions of packages to available versions, or vice versa. An easy way to see if you are up to date with what’s in your subscribed channels is nix-env -qc \*.
nix-env --query now takes as arguments a list of package names about which to show information, just like --install, etc.: for example, nix-env -q gcc. Note that to show all derivations, you need to specify \*.
nix-env -i will now install the highest available version of pkgnamepkgname, rather than installing all available versions (which would probably give collisions) (NIX-31).
nix-env (-i|-u) --dry-run now shows exactly which missing paths will be built or substituted.
nix-env -qa --description shows human-readable descriptions of packages, provided that they have a meta.description attribute (which most packages in Nixpkgs don’t have yet).
New language features:
Reference scanning (which happens after each build) is much faster and takes a constant amount of memory.
String interpolation. Expressions like
"--with-freetype2-library=" + freetype + "/lib"
can now be written as
"--with-freetype2-library=${freetype}/lib" You can write arbitrary expressions within ${, not just identifiers....}
Multi-line string literals.
String concatenations can now involve derivations, as in the example "--with-freetype2-library=" + freetype + "/lib". This was not previously possible because we need to register that a derivation that uses such a string is dependent on freetype. The evaluator now properly propagates this information. Consequently, the subpath operator (~) has been deprecated.
Default values of function arguments can now refer to other function arguments; that is, all arguments are in scope in the default values (NIX-45).
Lots of new built-in primitives, such as functions for list manipulation and integer arithmetic. See the manual for a complete list. All primops are now available in the set builtins, allowing one to test for the availability of primop in a backwards-compatible way.
Real let-expressions: let x = ...; ... z = ...; in ....
New commands nix-pack-closure and nix-unpack-closure than can be used to easily transfer a store path with all its dependencies to another machine. Very convenient whenever you have some package on your machine and you want to copy it somewhere else.
XML support:
nix-env -q --xml prints the installed or available packages in an XML representation for easy processing by other tools.
nix-instantiate --eval-only --xml prints an XML representation of the resulting term. (The new flag --strict forces ‘deep’ evaluation of the result, i.e., list elements and attributes are evaluated recursively.)
In Nix expressions, the primop builtins.toXML converts a term to an XML representation. This is primarily useful for passing structured information to builders.
You can now unambiguously specify which derivation to build or install in nix-env, nix-instantiate and nix-build using the --attr / -A flags, which takes an attribute name as argument. (Unlike symbolic package names such as subversion-1.4.0, attribute names in an attribute set are unique.) For instance, a quick way to perform a test build of a package in Nixpkgs is nix-build pkgs/top-level/all-packages.nix -A . foonix-env -q --attr shows the attribute names corresponding to each derivation.
If the top-level Nix expression used by nix-env, nix-instantiate or nix-build evaluates to a function whose arguments all have default values, the function will be called automatically. Also, the new command-line switch --arg can be used to specify function arguments on the command line.name value
nix-install-package --url allows a package to be installed directly from the given URL.URL
Nix now works behind an HTTP proxy server; just set the standard environment variables http_proxy, https_proxy, ftp_proxy or all_proxy appropriately. Functions such as fetchurl in Nixpkgs also respect these variables.
nix-build -o allows the symlink to the build result to be named something other than symlinkresult.
Platform support:
Support for 64-bit platforms, provided a suitably patched ATerm library is used. Also, files larger than 2 GiB are now supported.
Added support for Cygwin (Windows, i686-cygwin), Mac OS X on Intel (i686-darwin) and Linux on PowerPC (powerpc-linux).
Users of SMP and multicore machines will appreciate that the number of builds to be performed in parallel can now be specified in the configuration file in the build-max-jobs setting.
Garbage collector improvements:
Open files (such as running programs) are now used as roots of the garbage collector. This prevents programs that have been uninstalled from being garbage collected while they are still running. The script that detects these additional runtime roots (find-runtime-roots.pl) is inherently system-specific, but it should work on Linux and on all platforms that have the lsof utility.
nix-store --gc (a.k.a. nix-collect-garbage) prints out the number of bytes freed on standard output. nix-store --gc --print-dead shows how many bytes would be freed by an actual garbage collection.
nix-collect-garbage -d removes all old generations of all profiles before calling the actual garbage collector (nix-store --gc). This is an easy way to get rid of all old packages in the Nix store.
nix-store now has an operation --delete to delete specific paths from the Nix store. It won’t delete reachable (non-garbage) paths unless --ignore-liveness is specified.
Berkeley DB 4.4’s process registry feature is used to recover from crashed Nix processes.
A performance issue has been fixed with the referer table, which stores the inverse of the references table (i.e., it tells you what store paths refer to a given path). Maintaining this table could take a quadratic amount of time, as well as a quadratic amount of Berkeley DB log file space (in particular when running the garbage collector) (NIX-23).
Nix now catches the TERM and HUP signals in addition to the INT signal. So you can now do a killall nix-store without triggering a database recovery.
bsdiff updated to version 4.3.
Substantial performance improvements in expression evaluation and nix-env -qa, all thanks to Valgrind. Memory use has been reduced by a factor 8 or so. Big speedup by memoisation of path hashing.
Lots of bug fixes, notably:
Make sure that the garbage collector can run successfully when the disk is full (NIX-18).
nix-env now locks the profile to prevent races between concurrent nix-env operations on the same profile (NIX-7).
Removed misleading messages from nix-env -i (e.g., installing `foo' followed by uninstalling `foo') (NIX-17).
Nix source distributions are a lot smaller now since we no longer include a full copy of the Berkeley DB source distribution (but only the bits we need).
Header files are now installed so that external programs can use the Nix libraries.
This bug fix release fixes two problems on Mac OS X:
If Nix was linked against statically linked versions of the ATerm or Berkeley DB library, there would be dynamic link errors at runtime.
nix-pull and nix-push intermittently failed due to race conditions involving pipes and child processes with error messages such as open2: open(GLOB(0x180b2e4), >&=9) failed: Bad file descriptor at /nix/bin/nix-pull line 77 (issue NIX-14).
This bug fix release addresses a problem with the ATerm library when the --with-aterm flag in configure was not used.
NOTE: this version of Nix uses Berkeley DB 4.3 instead of 4.2. The database is upgraded automatically, but you should be careful not to use old versions of Nix that still use Berkeley DB 4.2. In particular, if you use a Nix installed through Nix, you should run
$ nix-store --clear-substitutes
first.
Unpacking of patch sequences is much faster now since we no longer do redundant unpacking and repacking of intermediate paths.
Nix now uses Berkeley DB 4.3.
The derivation primitive is lazier. Attributes of dependent derivations can mutually refer to each other (as long as there are no data dependencies on the outPath and drvPath attributes computed by derivation).
For example, the expression derivation attrs now evaluates to (essentially)
attrs // {
type = "derivation";
outPath = derivation! attrs;
drvPath = derivation! attrs;
} where derivation! is a primop that does the actual derivation instantiation (i.e., it does what derivation used to do). The advantage is that it allows commands such as nix-env -qa and nix-env -i to be much faster since they no longer need to instantiate all derivations, just the name attribute.
Also, it allows derivations to cyclically reference each other, for example,
webServer = derivation {
...
hostName = "svn.cs.uu.nl";
services = [svnService];
};
svnService = derivation {
...
hostName = webServer.hostName;
};Previously, this would yield a black hole (infinite recursion).
nix-build now defaults to using ./default.nix if no Nix expression is specified.
nix-instantiate, when applied to a Nix expression that evaluates to a function, will call the function automatically if all its arguments have defaults.
Nix now uses libtool to build dynamic libraries. This reduces the size of executables.
A new list concatenation operator ++. For example, [1 2 3] ++ [4 5 6] evaluates to [1 2 3 4 5 6].
Some currently undocumented primops to support low-level build management using Nix (i.e., using Nix as a Make replacement). See the commit messages for r3578 and r3580.
Various bug fixes and performance improvements.
This is a bug fix release.
Patch downloading was broken.
The garbage collector would not delete paths that had references from invalid (but substitutable) paths.
NOTE: the hashing scheme in Nix 0.8 changed (as detailed below). As a result, nix-pull manifests and channels built for Nix 0.7 and below will now work anymore. However, the Nix expression language has not changed, so you can still build from source. Also, existing user environments continue to work. Nix 0.8 will automatically upgrade the database schema of previous installations when it is first run.
If you get the error message
you have an old-style manifest `/nix/var/nix/manifests/[...]'; please delete it
you should delete previously downloaded manifests:
$ rm /nix/var/nix/manifests/*
If nix-channel gives the error message
manifest `http://catamaran.labs.cs.uu.nl/dist/nix/channels/[channel]/MANIFEST' is too old (i.e., for Nix <= 0.7)
then you should unsubscribe from the offending channel (nix-channel --remove URL; leave out /MANIFEST), and subscribe to the same URL, with channels replaced by channels-v3 (e.g., http://catamaran.labs.cs.uu.nl/dist/nix/channels-v3/nixpkgs-unstable).
Nix 0.8 has the following improvements:
The cryptographic hashes used in store paths are now 160 bits long, but encoded in base-32 so that they are still only 32 characters long (e.g., /nix/store/csw87wag8bqlqk7ipllbwypb14xainap-atk-1.9.0). (This is actually a 160 bit truncation of a SHA-256 hash.)
Big cleanups and simplifications of the basic store semantics. The notion of “closure store expressions” is gone (and so is the notion of “successors”); the file system references of a store path are now just stored in the database.
For instance, given any store path, you can query its closure:
$ nix-store -qR $(which firefox) ... lots of paths ...
Also, Nix now remembers for each store path the derivation that built it (the “deriver”):
$ nix-store -qR $(which firefox) /nix/store/4b0jx7vq80l9aqcnkszxhymsf1ffa5jd-firefox-1.0.1.drv
So to see the build-time dependencies, you can do
$ nix-store -qR $(nix-store -qd $(which firefox))
or, in a nicer format:
$ nix-store -q --tree $(nix-store -qd $(which firefox))
File system references are also stored in reverse. For instance, you can query all paths that directly or indirectly use a certain Glibc:
$ nix-store -q --referrers-closure \
/nix/store/8lz9yc6zgmc0vlqmn2ipcpkjlmbi51vv-glibc-2.3.4
The concept of fixed-output derivations has been formalised. Previously, functions such as fetchurl in Nixpkgs used a hack (namely, explicitly specifying a store path hash) to prevent changes to, say, the URL of the file from propagating upwards through the dependency graph, causing rebuilds of everything. This can now be done cleanly by specifying the outputHash and outputHashAlgo attributes. Nix itself checks that the content of the output has the specified hash. (This is important for maintaining certain invariants necessary for future work on secure shared stores.)
One-click installation :-) It is now possible to install any top-level component in Nixpkgs directly, through the web — see, e.g., http://catamaran.labs.cs.uu.nl/dist/nixpkgs-0.8/. All you have to do is associate /nix/bin/nix-install-package with the MIME type application/nix-package (or the extension .nixpkg), and clicking on a package link will cause it to be installed, with all appropriate dependencies. If you just want to install some specific application, this is easier than subscribing to a channel.
nix-store -r PATHS now builds all the derivations PATHS in parallel. Previously it did them sequentially (though exploiting possible parallelism between subderivations). This is nice for build farms.
nix-channel has new operations --list and --remove.
New ways of installing components into user environments:
Copy from another user environment:
$ nix-env -i --from-profile .../other-profile firefox
Install a store derivation directly (bypassing the Nix expression language entirely):
$ nix-env -i /nix/store/z58v41v21xd3...-aterm-2.3.1.drv
(This is used to implement nix-install-package, which is therefore immune to evolution in the Nix expression language.)
Install an already built store path directly:
$ nix-env -i /nix/store/hsyj5pbn0d9i...-aterm-2.3.1
Install the result of a Nix expression specified as a command-line argument:
$ nix-env -f .../i686-linux.nix -i -E 'x: x.firefoxWrapper'
The difference with the normal installation mode is that -E does not use the name attributes of derivations. Therefore, this can be used to disambiguate multiple derivations with the same name.
A hash of the contents of a store path is now stored in the database after a successful build. This allows you to check whether store paths have been tampered with: nix-store --verify --check-contents.
Implemented a concurrent garbage collector. It is now always safe to run the garbage collector, even if other Nix operations are happening simultaneously.
However, there can still be GC races if you use nix-instantiate and nix-store --realise directly to build things. To prevent races, use the --add-root flag of those commands.
The garbage collector now finally deletes paths in the right order (i.e., topologically sorted under the “references” relation), thus making it safe to interrupt the collector without risking a store that violates the closure invariant.
Likewise, the substitute mechanism now downloads files in the right order, thus preserving the closure invariant at all times.
The result of nix-build is now registered as a root of the garbage collector. If the ./result link is deleted, the GC root disappears automatically.
The behaviour of the garbage collector can be changed globally by setting options in /nix/etc/nix/nix.conf.
gc-keep-derivations specifies whether deriver links should be followed when searching for live paths.
gc-keep-outputs specifies whether outputs of derivations should be followed when searching for live paths.
env-keep-derivations specifies whether user environments should store the paths of derivations when they are added (thus keeping the derivations alive).
New nix-env query flags --drv-path and --out-path.
fetchurl allows SHA-1 and SHA-256 in addition to MD5. Just specify the attribute sha1 or sha256 instead of md5.
Manual updates.
Binary patching. When upgrading components using pre-built binaries (through nix-pull / nix-channel), Nix can automatically download and apply binary patches to already installed components instead of full downloads. Patching is “smart”: if there is a sequence of patches to an installed component, Nix will use it. Patches are currently generated automatically between Nixpkgs (pre-)releases.
Simplifications to the substitute mechanism.
Nix-pull now stores downloaded manifests in /nix/var/nix/manifests.
Metadata on files in the Nix store is canonicalised after builds: the last-modified timestamp is set to 0 (00:00:00 1/1/1970), the mode is set to 0444 or 0555 (readable and possibly executable by all; setuid/setgid bits are dropped), and the group is set to the default. This ensures that the result of a build and an installation through a substitute is the same; and that timestamp dependencies are revealed.
Rewrite of the normalisation engine.
Multiple builds can now be performed in parallel (option -j).
Distributed builds. Nix can now call a shell script to forward builds to Nix installations on remote machines, which may or may not be of the same platform type.
Option --fallback allows recovery from broken substitutes.
Option --keep-going causes building of other (unaffected) derivations to continue if one failed.
Improvements to the garbage collector (i.e., it should actually work now).
Setuid Nix installations allow a Nix store to be shared among multiple users.
Substitute registration is much faster now.
A utility nix-build to build a Nix expression and create a symlink to the result int the current directory; useful for testing Nix derivations.
Manual updates.
nix-env changes:
Derivations for other platforms are filtered out (which can be overridden using --system-filter).
--install by default now uninstall previous derivations with the same name.
--upgrade allows upgrading to a specific version.
New operation --delete-generations to remove profile generations (necessary for effective garbage collection).
Nicer output (sorted, columnised).
More sensible verbosity levels all around (builder output is now shown always, unless -Q is given).
Nix expression language changes:
New language construct: with brings all attributes defined in the attribute set E1; E2E1 in scope in E2.
Added a map function.
Various new operators (e.g., string concatenation).
Expression evaluation is much faster.
An Emacs mode for editing Nix expressions (with syntax highlighting and indentation) has been added.
Many bug fixes.
Please refer to the Subversion commit log messages.