jammy (7) initramfs-tools.7.gz

Provided by: initramfs-tools-core_0.140ubuntu13.4_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.

        initramfs.clear
              clear screen at the beginning

        initramfs.runsize
              The  size of the /run tmpfs mount point in bytes (suffixes are supported) or as percentage of your
              physical RAM. This parameter is used as  the  value  of  the  size  mount  option  to  tmpfs.  See
              https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt for details. The default is 10%.

        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.

        roottimeout
              set timeout in seconds. Determines how long mountroot waits for root to appear.  The default is 30
              seconds.

        rootdelay
              alias for roottimeout.

        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.

        vlan  tells  to create a VLAN tagged device. Allows one to configure one or multiple VLAN tagged devices
              using the "vlan=$name.$id:$parent" syntax. E.g.  "vlan=eth0.1:eth0"  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 an executable or shared library to the initramfs module, use a command like this:

              copy_exec /sbin/mdadm /sbin

       mkinitramfs will automatically detect which libraries it 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 NN-name Deprecated: This function is now a stub which is effectively a no-
              op. It will be removed in a future version; please remove mountroot failure  hooks  from  existing
              packages accordingly.

   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
              copy_exec /sbin/frobnicate /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.

UPDATING THE INITRAMFS FROM ANOTHER PACKAGE

       Package maintainer scripts should not run update-initramfs directly.  A package that installs  hooks  for
       initramfs-tools should include a triggers file containing:
              activate-noawait update-initramfs

       Kernel packages must call the kernel hooks as documented in the Debian Kernel Handbook.

       A  package that requires an initramfs to function, but is not a kernel package, should include a triggers
       file containing:
              activate-await update-initramfs

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).