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     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".

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           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.

           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.

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           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

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          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)

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          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

               # 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

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               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 automati-
          cally include glibc in the image which will increase its
          size by several hundred kilobytes.

        Including a system firmware preimage (early
          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 func-
          tion returns.

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

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

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           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, KEYMAP, 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 subdi-
          rectories 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

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               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 pro-
          vided 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 ini-
               tramfs image to allow the user to investigate the

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               situation.

               Example: panic "Frobnication failed"

        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 periodi-
               cally 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

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               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

               # 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

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               # 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

        Exported variables
          init sets several variables for the boot scripts environ-
          ment.

           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.

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           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 ini-
          tramfs is automatically created, updated or deleted as nec-
          essary.  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

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          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  H[:a]rdeman
          <david@hardeman.nu>, updated by Maximilian Attems
          <maks@debian.org>.

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

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