Provided by: initramfs-tools-core_0.130ubuntu3_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  one  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
              The resume hook tries to autodetect the resume partition and uses  the  first  swap
              partition   as  valid  guess.  It  is  possible  to  set  the  RESUME  variable  in
              /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 /run/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 the chosen phase (top, modules, premount,
              mount, mountroot, bottom, init) before actually executing the corresponding scripts
              (see  the  "Boot  scripts"  section)  or action.  Multiple phases may be specified,
              delimited by commas.  The default, if no phase is specified, is "premount".  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.

SCRIPTS

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

   Configuration hook scripts
       These  are  used  to override the user configuration where necessary, for example to force
       use of busybox instead of klibc utilities.

   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.

CONFIGURATION HOOK SCRIPTS

       Configuration hook scripts can be found in /usr/share/initramfs-tools/conf-hooks.d.   They
       are  sourced  by  mkinitramfs after the configuration files in /etc and before running any
       hook scripts.  They can override any of the variables documented in initramfs.conf(5), but
       this should be done only if absolutely necessary.  For example, if a package's boot script
       requires commands not provided by klibc-utils, it should also install a configuration hook
       that sets BUSYBOX=y.

HOOK SCRIPTS

       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.   Please  notice  that PREREQ is only honored inside a single
       directory.  So first the scripts in /usr/share/initramfs-tools are  ordered  according  to
       their  PREREQ  values  and  executed. Then all scripts in /etc/initramfs-tools are ordered
       according to their PREREQ values and executed.  This  mean  that  currently  there  is  no
       possibility to have a local script (/etc/initramfs-tools) get executed before one from the
       package (/usr/share/initramfs-tools).

       If a hook script requires configuration beyond the exported  variables  listed  below,  it
       should  read  a  private configuration file that is separate from the /etc/initramfs-tools
       directory.  It must not read initramfs-tools configuration files directly.

   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.

   Including a system firmware preimage (early initramfs)
       If  you need to prepend data to the initramfs image, you need to prepare it in a file, and
       call the prepend_earlyinitramfs function.  The file can be disposed  of  as  soon  as  the
       function returns.

       Example:
       TEMP_FILE=$(mktemp ...)
         ...
       prepend_earlyinitramfs ${TEMP_FILE}
       rm -f ${TEMP_FILE}

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

        MODULESDIR
              corresponds to the linux modules dir.

        version
              is the $(uname -r) linux 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.

        BUSYBOX, MODULES
              are as described in initramfs.conf(5).

        BUSYBOXDIR
              is  the  directory  where  busybox  utilities should be installed from, or empty if
              busybox is not being used.

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.  It also runs the udev hook for populating  the
              /dev tree (udev will keep running until init-bottom).

              init-premount   happens  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-block These scripts are called with the name of a local block device.   After
              these  scripts  have  been  executed,  that  device node should be present.  If the
              local-top or local-block scripts fail to create the wanted device node, the  local-
              block scripts will be called periodically to try again.

              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.

              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. udev is stopped.

   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.  Use of
              ROOTDELAY is deprecated; you should implement a local-block boot script rather than
              delaying or polling.

        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.

KERNEL HOOKS

       initramfs-tools  includes  hook scripts that are called by kernel packages on installation
       and removal, so that  an  initramfs  is  automatically  created,  updated  or  deleted  as
       necessary.   The  hook scripts do nothing if the environment variable INITRD is set to No.
       This  will  be  the  case  for  kernel  packages  built  with  make   deb-pkg   and   with
       CONFIG_BLK_DEV_INITRD  not set in the kernel config, or built with make-kpkg and not using
       the --initrd option.

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:
              lsinitramfs /boot/initrd.img-3.16-3-amd64

FILES

       /run/initramfs/fsck.log
              Log of fsck commands run within the initramfs, with their output.

       /run/initramfs/fsck-root
              Exists only if fsck ran successfully for the root filesystem.

       /run/initramfs/fsck-usr
              Exists only if fsck ran successfully for the /usr filesystem.

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   Härdeman  <david@hardeman.nu>,  updated  by  Maximilian
       Attems <maks@debian.org>.

SEE ALSO

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