Inferno (operating system)

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Inferno
Inferno 4th Edition
Developer	Bell Labs, Vita Nuova Holdings
Written in	C,[1] Limbo
Working state	Discontinued
Source model	Open-source
Initial release	1996; 30 years ago (1996)
Latest release	4th Edition / March 28, 2015; 11 years ago (2015-03-28)
Repository	github.com/inferno-os
Available in	English
Supported platforms	ARM, PA-RISC, MIPS, PowerPC, SPARC, x86
Kernel type	Virtual machine (Dis)
License	2021: MIT[2][3] 2005: Dual[a][4][5] 2003: Dual[b][6][7][8][9] 2000: Inferno[c][10] Original: Proprietary
Preceded by	Plan 9
Official website	www.inferno-os.org

Inferno is a distributed operating system started at Bell Labs and now developed and maintained by Vita Nuova Holdings as free software under the MIT License.^[2][3] Inferno was based on the experience gained with Plan 9 from Bell Labs, and the further research of Bell Labs into operating systems, languages, on-the-fly compilers, graphics, security, networking and portability. The name of the operating system, many of its associated programs, and that of the current company, were inspired by Dante Alighieri's Divine Comedy. In Italian, Inferno means "hell", of which there are nine circles in Dante's Divine Comedy.

Inferno was created in 1995 by members of Bell Labs' Computer Science Research division to bring ideas derived from their previous operating system, Plan 9 from Bell Labs, to a wider range of devices and networks. Inferno is a distributed operating system based on three basic principles:

• Resources as files: all resources are represented as files within a hierarchical file system
• Namespaces: a program's view of the network is a single, coherent namespace that appears as a hierarchical file system but may represent physically separated (locally or remotely) resources
• Standard communication protocol: a standard protocol, called Styx, is used to access all resources, both local and remote

To handle the diversity of network environments it was intended to be used in, the designers decided a virtual machine (VM) was a necessary component of the system. This is the same conclusion of the Oak project that became Java, but arrived at independently. The Dis virtual machine is a register machine intended to closely match the architecture it runs on, in contrast to the stack machine of the Java virtual machine. An advantage of this approach is the relative simplicity of creating a just-in-time compiler for new architectures.

The virtual machine provides memory management designed to be efficient on devices with as little as 1 MiB of memory and without memory-mapping hardware. Its garbage collector is a hybrid of reference counting and a real-time coloring collector that gathers cyclic data.^[11]

The Inferno kernel contains the virtual machine, on-the-fly compiler, scheduler, devices, protocol stacks, the name space evaluator for the file name space of each process, and the root of the file system hierarchy. The kernel also includes some built-in modules that provide interfaces of the virtual operating system, such as system calls, graphics, security, and math modules.

The Bell Labs Technical Journal paper introducing Inferno listed several dimensions of portability and versatility provided by the OS:^[1]

• Portability across processors: it currently runs on ARM, SGI MIPS, HP PA-RISC, IBM PowerPC, Sun SPARC, and Intel x86 architectures and is readily portable to others.
• Portability across environments: it runs as a stand-alone operating system on small terminals, and also as a user application under Bell Plan 9, MS Windows NT, Windows 95, and Unix (SGI Irix, Sun Solaris, FreeBSD, Apple Mac OS X, Linux, IBM AIX, HP-UX, Digital Tru64). In all of these environments, Inferno programs see an identical interface.
• Distributed design: the identical environment is established at the user's terminal and at the server, and each may import the resources (for example, the attached I/O devices or networks) of the other. Aided by the communications facilities of the run-time system, programs may be split easily (and even dynamically) between client and server.
• Minimal hardware requirements: it runs useful applications stand-alone on machines with as little as 1 MiB of memory, and does not require memory-mapping hardware.
• Portable programs: Inferno programs are written in the type-safe language Limbo and compiled to Dis bytecode, which can be run without modifications on all Inferno platforms.
• Dynamic adaptability: programs may, depending on the hardware or other resources available, load different program modules to perform a specific function. For example, a video player might use any of several different decoder modules.

These design choices were directed to provide standard interfaces that free content and service providers from concern of the details of diverse hardware, software, and networks over which their content is delivered.

This section needs expansion. You can help by adding missing information. (April 2019)

Inferno runs either as a native operating system or as a hosted application on several existing operating systems, including Linux, Windows, Plan 9, FreeBSD, Solaris, Mac OS X, and Irix. Supported processor architectures include Intel x86, ARM, PowerPC, and SPARC.^[12][13]

Applications are written in the Limbo programming language, which provides static typing, garbage collection, and built-in concurrency features. Limbo code is compiled into architecture-independent bytecode executed by the Dis virtual machine. The Dis VM can interpret the bytecode or compile it just-in-time into native instructions, allowing applications to run consistently across different platforms.^[12][13]

All resources in Inferno, such as devices, services, and network connections, are represented as files in a hierarchical namespace and accessed using standard file operations like open, read, write, and close. Inferno uses the Styx protocol, equivalent to Plan 9's 9P2000, to interact with both local and remote resources in a uniform manner.^[12][13]

Security features include per-process namespaces, authentication, and encryption. Applications operate within restricted namespaces, limiting their access to only authorized resources. The system supports a range of cryptographic protocols, including RSA, Diffie–Hellman, and symmetric encryption methods such as RC4 and DES.^[12]

Inferno provides a full development environment that includes a compiler, graphical debugger, scripting tools, and libraries for networking and user interfaces. It supports dynamic module loading and can operate with low resource requirements, such as systems with 1 MB of memory.^[12][13]

Inferno is a descendant of Plan 9 from Bell Labs, and shares many design concepts and even source code in the kernel, particularly around devices and the Styx/9P2000 protocol. Inferno shares with Plan 9 the Unix heritage from Bell Labs and the Unix philosophy. Many of the command line tools in Inferno were Plan 9 tools that were translated to Limbo.

In the mid-1990s, Plan 9 development was set aside in favor of Inferno.^[14] The new system's existence was leaked by Dennis Ritchie in early 1996, after less than a year of development on the system, and publicly presented later that year as a competitor to Java. At the same time, Bell Labs' parent company AT&T licensed Java technology from Sun Microsystems.^[15]

In March–April 1997 IEEE Internet Computing included an advertisement for Inferno networking software. It claimed that various devices could communicate over "any network" including the Internet, telecommunications and LANs. The advertisement stated that video games could talk to computers,–a PlayStation was pictured–cell phones could access email and voice mail was available via TV.

Lucent used Inferno in at least two internal products: the Lucent VPN Firewall Brick, and the Lucent Pathstar phone switch. They initially tried to sell source code licenses of Inferno but found few buyers. Lucent did little marketing and missed the importance of the Internet and Inferno's relation to it. During the same time Sun Microsystems was heavily marketing its own Java programming language, which was targeting a similar market, with analogous technology, that worked in web browsers and also filled the demand for object-oriented languages popular at that time. Lucent licensed Java from Sun, claiming that all Inferno devices would be made to run Java. A Java byte code to Dis byte code translator was written to facilitate that. However, Inferno still did not find customers.

The Inferno Business Unit closed after three years, and was sold to Vita Nuova Holdings. Vita Nuova continued development and offered commercial licenses to the complete system, and free downloads and licenses (not GPL compatible) for all of the system except the kernel and VM. They ported the software to new hardware and focused on distributed applications. Eventually, Vita Nuova released the 4th edition under more common free software licenses, and in 2021 they relicensed all editions under mainly the MIT License.^[6][2][3]

Inferno runs on native hardware directly and also as an application providing a virtual operating system which runs on other platforms. Programs can be developed and run on all Inferno platforms without modifying or recompiling.

Native ports include these architectures: x86, MIPS, ARM, PowerPC, SPARC.

Hosted or virtual OS ports include: Microsoft Windows, Linux, FreeBSD, Plan 9, Mac OS X, Solaris, IRIX, UnixWare.

Inferno can also be hosted by a plugin to Internet Explorer.^[16] Vita Nuova said that plugins for other browsers were under development, but they were never released.^[17]

Inferno has also been ported to Openmoko,^[18] Nintendo DS,^[19] SheevaPlug,^[20] and Android.^[21][22]

Inferno 4th edition was released in early 2005 as free software. Specifically, it was dual-licensed under two structures.^[6] Users could either obtain it under a set of free software licenses, or they could obtain it under a proprietary license. In the case of the free software license scheme, different parts of the system were covered by different licenses, including the GNU General Public License, the GNU Lesser General Public License, the Lucent Public License, and the MIT License, excluding the fonts, which are sub-licensed from Bigelow and Holmes.

In March 2021, all editions were relicensed under mainly the MIT License.^[2][3]

• Language-based system – Operating system that uses language features to provide security
• Singularity (operating system) – Experimental operating system from Microsoft Research

• Stanley-Marbell, Phillip (2003). Inferno Programming with Limbo. Chichester: John Wiley & Sons. ISBN 0-470-84352-7. describes the 3rd edition of the Inferno operating system, though it focuses more on the Limbo language and its interfaces to the Inferno system, than on the Inferno system itself. For example, it provides little information on Inferno's versatile command shell, which is understandable since it is a programming language textbook.
• Stuart, Brian (2008). Principles of Operating Systems: Design and Applications. Course Technology. ISBN 978-1-4188-3769-3., uses Inferno for examples of operating system design.
• Atkins, Martin; Forsyth, Charles; Pike, Rob; Trickey, Howard. The Inferno Programming Book: An Introduction to Programming for the Inferno Distributed System. was intended to provide an operating-system-centric point of view, but was never completed.

Wikimedia Commons has media related to Inferno (operating system).

• Documentation papers for the latest inferno release.
• Inferno Fourth Edition Download, including source code.
• Mailing list and other resources.
• Ninetimes: News and articles about Inferno, Plan 9 and related technologies.
• Inferno programmer's notebook - A journal made by an Inferno developer.
• Inferno OS to Raspberry Pi Labs: Porting Inferno OS to Raspberry Pi