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INITRAMFS-TOOLS(8)	  mkinitramfs script overview	    INITRAMFS-TOOLS(8)

       initramfs-tools - an introduction to writing scripts for mkinitramfs

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

       Valid boot and hook scripts names consist solely of alphabetics, numer
       ics 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

   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

       The script which is executed first and is  in  charge  of  running  all
       other scripts can be found in /usr/share/initramfs-tools/init. It takes
       a number of arguments which influence the boot procedure:

   Boot options
       The init and root are usually passed by the boot loader for local boot.
       The other parameters are optional.

	init  the  binary  to  hand over execution to on the root fs after the
	      initramfs scripts are done.

	root  the device node to mount as the root file  system.   The	recom
	      mended usage is to specify the UUID as followed "root=UUID=xxx".
	      As normal device names are not stable and may  change  depending
	      on the boot order.

	      set  delay  in  seconds. Determines how long mountroot waits for
	      root to appear.

	      set the file system mount option string.

	      set the root file system type.

	      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 dif
	      ferent NFS server than the DHCP server.  See  Documentation/nfs
	      root.txt	in any recent Linux source for details. Optional para
	      mater for NFS root.

	      passes the args for  cryptoroot.	Set  by  the  cryptsetup  boot

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

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

	      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.

	      disables load of specific modules.   Use	blacklist=module1,mod
	      ule2,module3 bootparameter.

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

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

	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.

	      loads generic IDE/ATA chipset support on boot.

       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.

       In order to support prereqs, each script should begin with the  follow
       ing lines:

		   echo "$PREREQ"

	      case $1 in
		   exit 0

	      . /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  func
       tions which deal with some common tasks in a hook script:

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

	      Example: manual_add_modules isofs

	      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

	      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

	      Example: force_load cdrom debug=1

	      copies an entire module directory  from  /lib/modules/KERNELVER
	      SION/ 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 exe
       cutables, unless compiled with klibc, will automatically include  glibc
       in the image which will increase its size by several hundred kilobytes.

       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.

       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:

		   echo "$PREREQ"

	      case $1 in
		   exit 0

       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

	      Logs a success message

	      Example: log_success_msg "Frobnication successful"

	      Logs a failure message

	      Example: log_failure_msg "Frobnication component froobz missing"

	      Logs a warning message

	      Example: log_warning_msg "Only partial frobnication possible"

	      Logs a message that some processing step has begun

	      Logs a message that some processing step is finished


		     log_begin_msg "Frobnication begun"
		     # Do something

       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"

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

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

	      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.

	      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
	      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.

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

	      # Example frobnication hook script

		   echo "$PREREQ"

	      case $1 in
		   exit 0

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

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

	      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  usu
       ally be placed in /etc/initramfs-tools/scripts/local-top/frobnicate):

	      # Example frobnication boot script

		   echo "$PREREQ"

	      case $1 in
		   exit 0

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

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

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

	      exit 0

       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 mod
	      mkdir tmp/initramfs
	      cd tmp/initramfs
	      gunzip -c /boot/initrd.img-2.6.18-1-686 | \
	      cpio -i -d -H newc --no-absolute-filenames

       The initramfs-tools are written by Maximilian Attems ,
       Jeff Bailey  and numerous others.

       This manual was written by David  Hrdeman , updated
       by Maximilian Attems .

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

				  2008/12/18		    INITRAMFS-TOOLS(8)

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