(cache) Fragrant Memories: My All-Purpose Init Script for initrd / initramfs Boot Images

Here I post my init script. It is used in my initrd/initramfs boot images for the following purposes.

Boot from a live CD / DVD
Boot from a read-only filesystem image, compressed in SquashFS
Copy the filesystem image to a RAM disk and run Linux entirely on memory
Boot Linux from a USB flash drive
Boot Linux from a local disk partition
Run a rescue shell without booting Linux

I have yet to implement network booting. Right now it is good enough for my current needs. It takes the following boot parameters.

root=
Specifies the root partition to boot Linux from. For example, /dev/sda2.
label=
Specifies the label of the device to boot from. For example, label=DEBIAN.
uuid=
Specifies the UUID of the device to boot from. For example, uuid=dcfd6a0a-2a0f-4b3d-8a1a-5e7d642ebfbd
boot=
Can be cdrom, loop, ram, usb or ata.
vmode=
Specifies the screen resolution of the framebuffer video. For example, vmode=640x480
single
Boot into the single-user mode.
nox
Boot into the console mode in runlevel 2

#!/bin/dash

# Define a function to parse kernel command line options.
get_opt() {
  echo $@ | cut -d "=" -f 2-
}

# Define a function to load drivers.
loadmod() {
  for i in $@ ; do
    for j in $(grep $i /tmp/pcimodules.txt); do
      modprobe $j
    done
  done
}

# Define a function to load drivers for USB controllers
modusb() {
  lspci -n | grep "0c03: " &&
  modprobe -a ohci-hcd uhci-hcd ehci-hcd xhci-hcd
}

# Define a function to guess the partition type.
gpart() {
  for i in $(blkid | grep $1); do
    case $i in
      *\=*)
        eval $i
        ;;
      *)
        true
        ;;
    esac
  done
}

# Define a function for mounting the root partition.
mountr() {
  if [ $uuid ]; then
    [ $# = 1 ] && mount -r -U $uuid $1 || mount -r -U $uuid /mnt
  elif [ $label ]; then
    [ $# = 1 ] && mount -r -L $label $1 || mount -r -L $label /mnt
  else
    gpart $1
    case $TYPE in
      ext*)
        e2fsck -p $1
        [ $# = 2 ] && mount $1 $2 || mount $1 /mnt
        ;;
      jfs)
        jfs_fsck $1
        if [ $# = 2 ]; then
          mount -t jfs -o ro,iocharset=utf8 $1 $2
        else mount -t jfs -o ro,iocharset=utf8 $1 /mnt
        fi
        ;;
      vfat)
        if [ $# = 2 ]; then
          mount -t vfat -o ro,gid=100,dmask=2,fmask=113 $1 $2
        else mount -t vfat -o ro,gid=100,dmask=2,fmask=113 $1 /mnt
        fi
        ;;
      *)
        [ $# = 2 ] && mount -r $1 $2 || mount -r $1 /mnt
        ;;
    esac
  fi
}

# Define a function for creating a union filesystem
union() {
  mount -t tmpfs none /opt/tmp
  modinfo unionfs > /dev/null 2>&1 &&
  mount -t unionfs -o dirs=/opt/tmp=rw:/opt=ro none /mnt ||
  ( mkdir /opt/tmp/.change
    modprobe fuse
    unionfs-fuse -o allow_other,use_ino,suid,dev,nonempty,kernel_cache \
     -o cow,chroot=/opt,max_files=32768 /tmp/.change=RW:/=RO /mnt )
  mount --rbind /opt /mnt/opt
}

# Mount proc and sysfs.
mount -t proc none /proc
mount -t sysfs none /sys

# Populate /dev (Needs kernel >= 2.6.32)
mount -t devtmpfs none /dev
mkdir -m 755 /dev/pts
mount -t devpts -o gid=5,mode=620 none /dev/pts

# Find modules required to use available PCI hardware
mount -t tmpfs none /tmp
for f in $(lspci -n | awk '{print toupper($3)}' | sed -e 's/:/d0000/g')
  do grep $f /lib/modules/$(uname -r)/modules.alias \
    | awk '{print $3}' >> /tmp/pcimodules.txt
done
lspci -n | awk '$2 == "0c00:" {print "firewire-ohci"}' >> /tmp/modules.txt

# Find the root=, label=, uuid= and boot= values on kernel command line.
for i in $(cat /proc/cmdline); do
  case $i in
    root\=*)
        root=$(get_opt $i)
        case $root in
          /dev/cdr* | /dev/dvd* | /dev/sr* | /dev/scd*)
            boot=cdrom
            ;;
          0x200)
            root=/dev/fd0
            ;;
          label\=* | LABEL\=* | uuid\=* | UUID\=* )
            eval $(echo $root | tr 'A-Z' 'a-z')
            ;;
        esac
        ;;
    label\=* | uuid\=* | boot\=* | vmode\=* )
        eval $i
        ;;
    single)
        RUNLEVEL=single
        ;;
    nox)
        RUNLEVEL=2
        ;;
  esac
done

# Set default values
[ "$boot" ] || boot=ata
[ "$uuid$label$root" ] || root=/dev/sda6

# Activate framebuffer display devices.
grep -q i915 /tmp/pcimodules.txt ||
if [ $vmode -a $boot = cdrom ]; then
    modprobe uvesafb scroll=ywrap mode_option=$vmode-16
elif [ $vmode ]; then
  for i in $(grep fb /tmp/pcimodules.txt); do
    case $i in
      atyfb)
        modprobe $i mode=$vmode-16
        ;;
      nvidiafb | rivafb)
        modprobe nvidiafb mode_option=$vmode bpp=16 hwcur=1
        ;;
      radeonfb | savagefb)
        modprobe $i mode_option=$vmode-16
        ;;
      sisfb)
        modprobe $i mode=$vmodex16 mem=12288 font=SUN12x22
        ;;
      viafb | vt8623fb)
        modprobe viafb viafb_mode=$vmode viafb_bpp=16
        ;;
      *)
        modprobe $i
        ;;
    esac
  done
  [ -c /dev/fb0 ] || modprobe uvesafb scroll=ywrap mode_option=$vmode-16
fi

case $boot in
    cdrom)
        # Boot Linux from a live CD.
        loadmod ata_ ahci pdc_adma
        modusb
        modprobe usb-storage &&
        modprobe sr_mod &&
        sleep 7
        modprobe isofs
        mount -t iso9660 /dev/sr0 /media
        [ -d /media/isolinux -o -d /media/boot/isolinux ] || 
          mount -t iso9660 /dev/sr1 /media
        if [ -f /media/*.[Ss][Qq]* ]; then
          SQF=$(ls -t /media/*.[Ss][Qq]* | head -n 1)
          if [ $root = /dev/ram ]; then 
               echo "Please wait until the RAM disk is ready."
               dd if=$SQF of=/dev/ram1 bs=2048 &&
               mount -t squashfs /dev/ram1 /opt
          else modprobe loop
               mount -t squashfs -o loop $SQF /opt
          fi
        else
          mount --move /media /opt
        fi
        union
        ;;
    loop)
        # Boot Linux from an image file.
        loadmod ata_ ahci pdc_adma
        modusb
        modprobe usb-storage &&
        modprobe sd_mod &&
        sleep 7
        [ "$uuid$label" ] && mountr /media || mountr $root /media
        modprobe loop
        if [ -f /media/*.[Ss][Qq]* ]; then
          SQF=$(ls -t /media/*.[Ss][Qq]* | head -n 1)
          mount -t squashfs -o loop $SQF /opt
        elif [ -f /media/*.[Ii][Ss][Oo] ]; then
          ISO=$(ls -t /media/*.[Ii][Ss][Oo] | head -n 1)
          modprobe isofs
          mount -t iso9660 -o loop $ISO /opt
        fi
        union
        ;;
    ram)
        # Boot Linux from ramdisk.
        loadmod ata_ ahci pdc_adma
        modusb
        modprobe usb-storage &&
        modprobe sd_mod &&
        sleep 7
        [ "$uuid$label" ] && mountr /media || mountr $root /media
        echo "Please wait until the RAM disk is ready."
        if [ -f /media/*.[Ss][Qq]* ]; then
          SQF=$(ls -t /media/*.[Ss][Qq]* | head -n 1)
          dd if=$SQF of=/dev/ram1 &&
          mount -t squashfs /dev/ram1 /opt
        elif [ -f /media/*.[Ii][Ss][Oo] ]; then
          ISO=$(ls -t /media/*.[Ii][Ss][Oo] | head -n 1)
          dd if=$ISO of=/dev/ram1 bs=2048 &&
          modprobe isofs
          mount -t iso9660 /dev/ram1 /opt
        fi
        union
        ;;
    usb*)
        # Boot Linux from a USB drive.
        modusb
        modprobe usb-storage &&
        modprobe sd_mod &&
        sleep 7
        [ "$uuid$label" ] && mountr || mountr $root
        ;;
    ata*)
        loadmod ata_ ahci pdc_adma &&
        modprobe sd_mod &&
        [ "$uuid$label" ] && mountr || mountr $root
        ;;
esac

# Make sure that init exists and is executable.
if [ -x /mnt/sbin/init ]; then
  mount --move /dev /mnt/dev
  mount --move /proc /mnt/proc
  mount --move /sys /mnt/sys
  umount /tmp

# Start init from the root filesystem.
  cd /mnt
  [ -f /media/updates.zip ] && unzip -o /media/updates.zip
  case $boot in
    cdrom)
      [ $root = /dev/ram ] && umount /media
      [ $RUNLEVEL ] || RUNLEVEL=3
      ;;
    loop | ram)
      umount /media
      [ $RUNLEVEL ] || RUNLEVEL=3
      ;;
    *)
      [ $RUNLEVEL ] || RUNLEVEL=5
      ;;
  esac
  [ -d initrd ] && pivot_root . initrd
  exec switch_root . /sbin/init $RUNLEVEL dev/console 2>&1
fi

# Start a shell as a last resort.
echo "Error booting from the root filesystem. Starting a shell."
exec /bin/dash

The following are examples of boot parameters that can be used with my init script.

Boot Linux from the local hard drive partition /dev/sda8
```
boot=ata root=/dev/sda8
```
Boot Linux from the latest squashfs file (*.sq*) on /dev/sda1
```
boot=loop root=/dev/sda1
```
Boot Linux from the CD-ROM with 1024x768 video resolution
```
boot=cdrom vmode=1024x768
```
Copy the squashfs image from CD-ROM into memory and run Linux on memory
```
boot=cdrom root=/dev/ram ramdisk_size=573440 vmode=800x600
```
Boot Linux from the second partition of a USB drive
```
boot=usb root=/dev/sda2
```