Provided by: initramfs-tools_0.98.1ubuntu6_all bug

NAME

       initramfs-tools - an introduction to writing scripts for mkinitramfs

DESCRIPTION

       initramfs-tools   has  one  main  script  and  two  different  sets  of
       subscripts which will be used during  different  phases  of  execution.
       Each  of  these  will be discussed separately below with the help of an
       imaginary tool which performs a frobnication of a lvm  partition  prior
       to mounting the root partition.

Kernel Command Line

       The  root filesystem used by the kernel is specified by the boot loader
       as always. The traditional root=/dev/sda1 style device specification is
       allowed.  If a label is used, as in root=LABEL=rootPart the initrd will
       search all available devices for  a  filesystem  with  the  appropriate
       label,    and    mount    that   device   as   the   root   filesystem.
       root=UUID=uuidnumber will mount the partition with  that  UUID  as  the
       root filesystem.

   Standard
        init= "<path to real init>"
              the  binary  to  hand over execution to on the root fs after the
              initramfs scripts are done.

        root= "<path to blockdevice>"
              the  device  node  to  mount  as  the  root  file  system.   The
              recommended   usage   is   to   specify  the  UUID  as  followed
              "root=UUID=xxx".

        rootfstype
              set the root file system type.

        rootdelay
              set delay in seconds. Determines how long  mountroot  waits  for
              root to appear.  The default is 180 seconds.

        rootflags
              set the file system mount option string.

        loop= "<path to image>"
              path  within the original root file system to loop-mount and use
              as the real root file system.

        loopfstype
              set the loop file system type, if applicable.

        loopflags
              set the loop file system mount option string, if applicable.

        nfsroot
              can be either "auto" to try to get the relevant information from
              DHCP   or   a   string   of   the   form   NFSSERVER:NFSPATH  or
              NFSSERVER:NFSPATH:NFSOPTS.  Use root=/dev/nfs for NFS to kick to
              in. NFSOPTS can be looked up in nfs(5).

        ip    tells  how  to  configure  the  ip address. Allows to specify an
              different   NFS   server   than    the    DHCP    server.    See
              Documentation/filesystems/nfsroot.txt in any recent Linux source
              for details. Optional parameter for NFS root.

        BOOTIF
              is a mac address in pxelinux format with leading "01-"  and  "-"
              as  separations.   pxelinux  passes  mac address of network card
              used to PXE boot on with this bootarg.

        boot  either local or NFS (affects which initramfs  scripts  are  run,
              see the "Subdirectories" section under boot scripts).

        resume
              On  install  initramfs-tools  tries  to  autodetect  the  resume
              partition.  On  success  the  RESUME  variable  is  written   to
              /etc/initramfs-tools/conf.d/resume.   The boot variable noresume
              overrides it.

        resume_offset
              Specify the offset from the  partition  given  by  "resume="  at
              which the swap header of the swap file is located.

        quiet reduces the amount of text output to the console during boot.

        ro    mounts the rootfs read-only.

        rw    mounts the rootfs read-write.

        blacklist
              disables      load      of      specific      modules.       Use
              blacklist=module1,module2,module3 bootparameter.

   Debug
        panic sets an timeout on panic.  panic=<sec> is a documented  security
              feature: it disables the debug shell.

        debug generates    lots    of    output.    It   writes   a   log   to
              /dev/.initramfs/initramfs.debug.  Instead when invoked  with  an
              arbitrary  argument  output  is  written  to  console.   Use for
              example "debug=vc".

        break spawns a shell in the initramfs image at chosen  run-time  (top,
              modules, premount, mount, mountroot, bottom, init).  The default
              is premount without any arg.  Beware that if  both  "panic"  and
              "break"  are  present,  initramfs  will not spawn any shells but
              reboot instead.

        netconsole
              loads netconsole linux modules with the chosen args.

        all_generic_ide
              loads generic IDE/ATA chipset support on boot.

HOOK SCRIPTS

       Valid boot and  hook  scripts  names  consist  solely  of  alphabetics,
       numerics, dashes and underscores. Other scripts are discarded.

   Hook scripts
       These  are  used when an initramfs image is created and not included in
       the image itself. They can however cause files to be  included  in  the
       image.  Hook scripts are executed under errexit. Thus a hook script can
       abort the mkinitramfs build on possible errors (exitcode != 0).

   Boot scripts
       These are included in the initramfs image and normally executed  during
       kernel  boot in the early user-space before the root partition has been
       mounted.

       Hooks can be found in two places: /usr/share/initramfs-tools/hooks  and
       /etc/initramfs-tools/hooks.  They are executed during generation of the
       initramfs-image and are responsible for  including  all  the  necessary
       components  in the image itself. No guarantees are made as to the order
       in which the different scripts are  executed  unless  the  prereqs  are
       setup in the script.

   Header
       In  order  to  support  prereqs,  each  script  should  begin  with the
       following lines:

              #!/bin/sh
              PREREQ=""
              prereqs()
              {
                   echo "$PREREQ"
              }

              case $1 in
              prereqs)
                   prereqs
                   exit 0
                   ;;
              esac

              . /usr/share/initramfs-tools/hook-functions
              # Begin real processing below this line

       For example, if you are writing a new hook script which relies on  lvm,
       the  line  starting with PREREQ should be changed to PREREQ="lvm" which
       will ensure that the lvm hook script is run before your custom script.

   Help functions
       /usr/share/initramfs-tools/hook-functions   contains   a   number    of
       functions which deal with some common tasks in a hook script:

              manual_add_modules  adds  a  module  (and  any  modules which it
              depends on) to the initramfs image.

              Example: manual_add_modules isofs

              add_modules_from_file reads a file containing a list of  modules
              (one  per line) to be added to the initramfs image. The file can
              contain comments (lines starting with #) and  arguments  to  the
              modules by writing the arguments on the same line as the name of
              the module.

              Example: add_modules_from_file /tmp/modlist

              force_load adds a module (and its dependencies) to the initramfs
              image  and  also  unconditionally  loads the module during boot.
              Also supports passing arguments to the module  by  listing  them
              after the module name.

              Example: force_load cdrom debug=1

              copy_modules_dir   copies   an   entire  module  directory  from
              /lib/modules/KERNELVERSION/ into the initramfs image.

              Example: copy_modules_dir kernel/drivers/ata

   Including binaries
       If you need to copy binaries to the initramfs module,  a  command  like
       this should be used:

              copy_exec /sbin/mdadm /sbin

       mkinitramfs  will  automatically  detect which libraries the executable
       depends on and copy  them  to  the  initramfs.  This  means  that  most
       executables,  unless  compiled  with  klibc, will automatically include
       glibc in the image which will increase  its  size  by  several  hundred
       kilobytes.

   Exported variables
       mkinitramfs sets several variables for the hook scripts environment.

        MODULESDIR
              corresponds to the linux-2.6 modules dir.

        version
              is the $(uname -r) linux-2.6 version against mkinitramfs is run.

        CONFDIR
              is the path of the used initramfs-tools configurations.

        DESTDIR
              is the root path of the newly build initramfs.

        DPKG_ARCH
              allows arch specific hook additions.

        verbose
              corresponds to the verbosity of the update-initramfs run.

        MODULES
              specifies  which kind of modules should land on initramfs.  This
              setting shouldn't be overridden by hook script,  but  can  guide
              them on how much they need to include on initramfs.

BOOT SCRIPTS

       Similarly  to  hook  scripts,  boot  scripts can be found in two places
       /usr/share/initramfs-tools/scripts/ and  /etc/initramfs-tools/scripts/.
       There  are  a  number  of subdirectories to these two directories which
       control the boot stage at which the scripts are executed.

   Header
       Like for hook scripts, there are no guarantees as to the order in which
       the  different scripts in one subdirectory (see "Subdirectories" below)
       are executed. In order to define a certain order, a similar  header  as
       for hook scripts should be used:

              #!/bin/sh
              PREREQ=""
              prereqs()
              {
                   echo "$PREREQ"
              }

              case $1 in
              prereqs)
                   prereqs
                   exit 0
                   ;;
              esac

       Where PREREQ is modified to list other scripts in the same subdirectory
       if necessary.

   Help functions
       A number of functions (mostly dealing with output) are provided to boot
       scripts in /scripts/functions :

              log_success_msg Logs a success message

              Example: log_success_msg "Frobnication successful"

              log_failure_msg Logs a failure message

              Example: log_failure_msg "Frobnication component froobz missing"

              log_warning_msg Logs a warning message

              Example: log_warning_msg "Only partial frobnication possible"

              log_begin_msg Logs a message that some processing step has begun

              log_end_msg Logs a message that some processing step is finished

              Example:

                     log_begin_msg "Frobnication begun"
                     # Do something
                     log_end_msg

              panic  Logs  an  error  message  and  executes  a  shell  in the
              initramfs image to allow the user to investigate the situation.

              Example: panic "Frobnication failed"

              add_mountroot_fail_hook Registers the script as able to  provide
              possible  further information, in the event that the root device
              cannot be found. See the example script in  the  initramfs-tools
              examples directory for more information.

              Example: add_mountroot_fail_hook

   Subdirectories
       Both     /usr/share/initramfs-tools/scripts     and     /etc/initramfs-
       tools/scripts contains the following subdirectories.

              init-top the scripts in this directory are the first scripts  to
              be  executed  after  sysfs  and  procfs  have  been  mounted and
              /dev/console and /dev/null have been created.  No  other  device
              files are present yet.

              init-premount  runs  the udev hooks for populating the /dev tree
              (udev  will  keep  running  until  init-bottom)  after   modules
              specified  by  hooks  and /etc/initramfs-tools/modules have been
              loaded.

              local-top OR nfs-top After these scripts have been executed, the
              root  device  node  is  expected  to  be  present (local) or the
              network interface is expected to be usable (NFS).

              local-premount OR nfs-premount are run after the sanity  of  the
              root  device  has been verified (local) or the network interface
              has been brought up (NFS), but before the  actual  root  fs  has
              been mounted.

              local-bottom  OR  nfs-bottom  are  run after the rootfs has been
              mounted (local) or the NFS root share has been mounted. udev  is
              stopped.

              init-bottom  are  the  last scripts to be executed before procfs
              and sysfs are moved to the real rootfs and execution  is  turned
              over to the init binary which should now be found in the mounted
              rootfs.

   Boot parameters
              /conf/param.conf  allows  boot  scripts   to   change   exported
              variables  that  are listed on top of init. Write the new values
              to it. It will be sourced after an boot script run if it exists.

EXAMPLES

   Hook script
       An example hook script  would  look  something  like  this  (and  would
       usually be placed in /etc/initramfs-tools/hooks/frobnicate):

              #!/bin/sh
              # Example frobnication hook script

              PREREQ="lvm"
              prereqs()
              {
                   echo "$PREREQ"
              }

              case $1 in
              prereqs)
                   prereqs
                   exit 0
                   ;;
              esac

              . /usr/share/initramfs-tools/hook-functions
              # Begin real processing below this line

              if [ ! -x "/sbin/frobnicate" ]; then
                   exit 0
              fi

              force_load frobnicator interval=10
              cp /sbin/frobnicate "${DESTDIR}/sbin"
              exit 0

   Boot script
       An  example  boot  script  would  look  something  like this (and would
       usually    be     placed     in     /etc/initramfs-tools/scripts/local-
       top/frobnicate):

              #!/bin/sh
              # Example frobnication boot script

              PREREQ="lvm"
              prereqs()
              {
                   echo "$PREREQ"
              }

              case $1 in
              prereqs)
                   prereqs
                   exit 0
                   ;;
              esac

              . /scripts/functions
              # Begin real processing below this line
              if [ ! -x "/sbin/frobnicate" ]; then
                   panic "Frobnication executable not found"
              fi

              if [ ! -e "/dev/mapper/frobb" ]; then
                   panic "Frobnication device not found"
              fi

              log_begin_msg "Starting frobnication"
              /sbin/frobnicate "/dev/mapper/frobb" || panic "Frobnication failed"
              log_end_msg

              exit 0

   Exported variables
       init sets several variables for the boot scripts environment.

        ROOT  corresponds to the root boot option.  Advanced boot scripts like
              cryptsetup or live-initramfs need  to  play  tricks.   Otherwise
              keep it alone.

        ROOTDELAY, ROOTFLAGS, ROOTFSTYPE, IP
              corresponds  to  the rootdelay, rootflags, rootfstype or ip boot
              option.

        DPKG_ARCH
              allows arch specific boot actions.

        blacklist, panic, quiet, resume, noresume, resume_offset
              set according relevant boot option.

        break Useful for manual intervention during setup and coding  an  boot
              script.

        REASON
              Argument  passed  to the panic helper function.  Use to find out
              why you landed in the initramfs shell.

        init  passes the path to init(8) usually /sbin/init.

        readonly
              is the default for mounting  the  root  corresponds  to  the  ro
              bootarg.  Overridden by rw bootarg.

        rootmnt
              is the path where root gets mounted usually /root.

        debug indicates   that   a   debug   log   is   captured  for  further
              investigation.

DEBUG

       It is easy to check the generated initramfs for its  content.  One  may
       need  to  double-check  if  it  contains the relevant binaries, libs or
       modules:
              mkdir tmp/initramfs
              cd tmp/initramfs
              gunzip -c /boot/initrd.img-2.6.18-1-686 | \
              cpio -i -d -H newc --no-absolute-filenames

AUTHOR

       The initramfs-tools are written by Maximilian Attems <maks@debian.org>,
       Jeff Bailey <jbailey@raspberryginger.com> and numerous others.

       This manual was written by David  Hardeman <david@hardeman.nu>, updated
       by Maximilian Attems <maks@debian.org>.

SEE ALSO

        initramfs.conf(5), mkinitramfs(8), update-initramfs(8).