initramfs-tools

DESCRIPTION
       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
       image.


   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.


INIT SCRIPT
       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.


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


         rootflags
              set the file system mount option string.


         rootfstype
              set the root file system type.


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


         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.


         cryptopts
              passes  the  args  for  cryptoroot.  Set  by the cryptsetup boot
              hooks.


         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 parti-
              tion.  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,mod-
              ule2,module3 bootparameter.


         panic
              sets an timeout on panic.  panic=0 is a documented security fea-
              ture: it disables the debug shell.




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 set-
       up in the script.


   Header
       In  order to support prereqs, each script should begin with the follow-
       ing 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  func-
       tions 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

              Example: force_load cdrom debug=1



       copy_modules_dir
              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.



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.



       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  infor-
              mation,  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.


              /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  usu-
       ally be placed in /etc/initramfs-tools/hooks/frobnicate):

              #!/bin/sh
              # Example frobnication hook script

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

              case $1 in
              prereqs)
              force_load frobnicator interval=10
              cp /sbin/frobnicate "${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):

              #!/bin/sh
              # Example frobnication boot script

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

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

              # 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


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 mod-
       ules:
              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>,