545 lines
13 KiB
Groff
545 lines
13 KiB
Groff
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.TH INITRAMFS-TOOLS 8 "2009/02/23" "Linux" "mkinitramfs script overview"
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.SH NAME
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initramfs-tools \- an introduction to writing scripts for mkinitramfs
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.SH DESCRIPTION
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initramfs-tools has one main script and two different sets of subscripts which
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will be used during different phases of execution. Each of these will be
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discussed separately below with the help of an imaginary tool which performs a
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frobnication of a lvm partition prior to mounting the root partition.
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Valid boot and hook scripts names consist solely of alphabetics, numerics
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and underscores. Other scripts are discarded.
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.SS Hook scripts
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These are used when an initramfs image is created and not included in the
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image itself. They can however cause files to be included in the image.
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.SS Boot scripts
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These are included in the initramfs image and normally executed during
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kernel boot in the early user-space before the root partition has been
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mounted.
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.SH INIT SCRIPT
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The script which is executed first and is in charge of running all other
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scripts can be found in /usr/share/initramfs-tools/init. It takes a number of
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arguments which influence the boot procedure:
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.SS Boot options
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The init and root are usually passed by the boot loader for local boot.
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The other parameters are optional.
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.TP
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\fB\fI init
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the binary to hand over execution to on the root fs after the initramfs scripts are done.
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.TP
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\fB\fI root
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the device node to mount as the root file system.
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The recommended usage is to specify the UUID as followed "root=UUID=xxx".
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As normal device names are not stable and may change depending on the
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boot order.
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.TP
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\fB\fI rootdelay
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set delay in seconds. Determines how long mountroot waits for root to appear.
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The default is 180 seconds.
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.TP
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\fB\fI rootflags
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set the file system mount option string.
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.TP
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\fB\fI rootfstype
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set the root file system type.
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.TP
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\fB\fI nfsroot
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can be either "auto" to try to get the relevant information from DHCP or a
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string of the form NFSSERVER:NFSPATH or NFSSERVER:NFSPATH:NFSOPTS.
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Use root=/dev/nfs for NFS to kick to in. NFSOPTS can be looked up in
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\fInfs(5)\fP.
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.TP
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\fB\fI ip
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tells how to configure the ip address. Allows to specify an different
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NFS server than the DHCP server. See Documentation/nfsroot.txt in
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any recent Linux source for details. Optional paramater for NFS root.
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.TP
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\fB\fI cryptopts
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passes the args for cryptoroot. Set by the cryptsetup boot hooks.
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.TP
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\fB\fI boot
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either local or NFS (affects which initramfs scripts are run, see the "Subdirectories" section under boot scripts).
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.TP
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\fB\fI resume
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On install initramfs-tools tries to autodetect the resume partition. On success
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the RESUME variable is written to /etc/initramfs-tools/conf.d/resume.
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The boot variable noresume overrides it.
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.TP
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\fB\fI resume_offset
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Specify the offset from the partition given by "resume=" at which the swap
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header of the swap file is located.
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.TP
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\fB\fI quiet
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reduces the amount of text output to the console during boot.
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.TP
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\fB\fI ro
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mounts the rootfs read-only.
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.TP
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\fB\fI rw
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mounts the rootfs read-write.
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.TP
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\fB\fI blacklist
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disables load of specific modules.
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Use blacklist=module1,module2,module3 bootparameter.
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.TP
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\fB\fI panic
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sets an timeout on panic.
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panic=<sec> is a documented security feature: it disables the debug shell.
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.TP
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\fB\fI debug
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generates lots of output. It writes a log to /dev/.initramfs/initramfs.debug.
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Instead when invoked with an arbitrary argument output is written to console.
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Use for example "debug=vc".
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.TP
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\fB\fI break
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spawns a shell in the initramfs image at chosen run-time
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(top, modules, premount, mount, mountroot, bottom, init).
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The default is premount without any arg.
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Beware that if both "panic" and "break" are present,
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initramfs will not spawn any shells but reboot instead.
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.TP
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\fB\fI all_generic_ide
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loads generic IDE/ATA chipset support on boot.
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.SH HOOK SCRIPTS
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Hooks can be found in two places: /usr/share/initramfs-tools/hooks and
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/etc/initramfs-tools/hooks. They are executed during generation of the
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initramfs-image and are responsible for including all the necessary components
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in the image itself. No guarantees are made as to the order in which the
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different scripts are executed unless the prereqs are setup in the script.
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.SS Header
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In order to support prereqs, each script should begin with the following lines:
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.RS
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.nf
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#!/bin/sh
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PREREQ=""
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prereqs()
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{
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echo "$PREREQ"
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}
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case $1 in
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prereqs)
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prereqs
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exit 0
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;;
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esac
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\fR. /usr/share/initramfs-tools/hook-functions
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# Begin real processing below this line
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.fi
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.RE
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For example, if you are writing a new hook script which relies on lvm, the line
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starting with PREREQ should be changed to PREREQ="lvm" which will ensure that
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the lvm hook script is run before your custom script.
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.SS Help functions
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/usr/share/initramfs-tools/hook-functions contains a number of functions which
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deal with some common tasks in a hook script:
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.TP
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\fB\fI
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manual_add_modules
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adds a module (and any modules which it depends on) to the initramfs image.
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.RS
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.PP
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.B Example:
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manual_add_modules isofs
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.RE
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.TP
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\fB\fI
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add_modules_from_file
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reads a file containing a list of modules (one per line) to be added to the
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initramfs image. The file can contain comments (lines starting with #) and
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arguments to the modules by writing the arguments on the same line as the name
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of the module.
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.RS
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.PP
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.B Example:
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add_modules_from_file /tmp/modlist
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.RE
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.TP
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\fB\fI
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force_load
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adds a module (and its dependencies) to the initramfs image and also
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unconditionally loads the module during boot. Also supports passing arguments
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to the module by listing them after the module name.
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.RS
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.PP
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.B Example:
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force_load cdrom debug=1
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.RE
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.TP
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\fB\fI
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copy_modules_dir
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copies an entire module directory from /lib/modules/KERNELVERSION/ into the
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initramfs image.
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.RS
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.PP
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.B Example:
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copy_modules_dir kernel/drivers/ata
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.RE
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.SS Including binaries
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If you need to copy binaries to the initramfs module, a command like this
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should be used:
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.PP
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.RS
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copy_exec /sbin/mdadm /sbin
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.RE
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mkinitramfs will automatically detect which libraries the executable depends on
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and copy them to the initramfs. This means that most executables, unless
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compiled with klibc, will automatically include glibc in the image which will
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increase its size by several hundred kilobytes.
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.SS Exported variables
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mkinitramfs sets several variables for the hook scripts environment.
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.TP
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\fB\fI MODULESDIR
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corresponds to the linux-2.6 modules dir.
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.TP
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\fB\fI version
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is the $(uname -r) linux-2.6 version against mkinitramfs is run.
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.TP
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\fB\fI CONFDIR
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is the path of the used initramfs-tools configurations.
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.TP
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\fB\fI DESTDIR
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is the root path of the newly build initramfs.
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.TP
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\fB\fI DPKG_ARCH
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allows arch specific hook additions.
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.TP
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\fB\fI verbose
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corresponds to the verbosity of the update-initramfs run.
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.TP
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\fB\fI KEYMAP
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sets if a keymap needs to be added to initramfs.
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.TP
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\fB\fI MODULES
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specifies which kind of modules should land on initramfs.
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This setting shouldn't be overriden by hook script, but can guide them
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on how much they need to include on initramfs.
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.SH BOOT SCRIPTS
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Similarly to hook scripts, boot scripts can be found in two places
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/usr/share/initramfs-tools/scripts/ and /etc/initramfs-tools/scripts/. There
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are a number of subdirectories to these two directories which control the boot
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stage at which the scripts are executed.
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.SS Header
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Like for hook scripts, there are no guarantees as to the order in which the
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different scripts in one subdirectory (see "Subdirectories" below) are
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executed. In order to define a certain order, a similar header as for hook
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scripts should be used:
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.RS
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.nf
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#!/bin/sh
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PREREQ=""
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prereqs()
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{
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echo "$PREREQ"
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}
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case $1 in
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prereqs)
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prereqs
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exit 0
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;;
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esac
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.fi
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.RE
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Where PREREQ is modified to list other scripts in the same subdirectory if necessary.
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.SS Help functions
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A number of functions (mostly dealing with output) are provided to boot scripts:
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.TP
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\fB\fI
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log_success_msg
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Logs a success message
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.RS
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.PP
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.B Example:
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log_success_msg "Frobnication successful"
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.RE
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.TP
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\fB\fI
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log_failure_msg
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Logs a failure message
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.RS
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.PP
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.B Example:
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log_failure_msg "Frobnication component froobz missing"
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.RE
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.TP
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\fB\fI
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log_warning_msg
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Logs a warning message
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.RS
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.PP
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.B Example:
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log_warning_msg "Only partial frobnication possible"
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.RE
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.TP
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\fB\fI
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log_begin_msg
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Logs a message that some processing step has begun
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.TP
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\fB\fI
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log_end_msg
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Logs a message that some processing step is finished
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.RS
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.PP
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.B Example:
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.PP
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.RS
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.nf
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log_begin_msg "Frobnication begun"
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# Do something
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log_end_msg
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.fi
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.RE
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.RE
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.TP
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\fB\fI
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panic
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Logs an error message and executes a shell in the initramfs image to allow the
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user to investigate the situation.
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.RS
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.PP
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.B Example:
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panic "Frobnication failed"
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.RE
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.SS Subdirectories
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Both /usr/share/initramfs-tools/scripts and /etc/initramfs-tools/scripts
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contains the following subdirectories.
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.TP
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\fB\fI
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init-top
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the scripts in this directory are the first scripts to be executed after sysfs
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and procfs have been mounted and /dev/console and /dev/null have been created.
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No other device files are present yet.
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.TP
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\fB\fI
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init-premount
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runs the udev hooks for populating the /dev tree (udev will keep running until
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init-bottom) after modules specified by hooks and /etc/initramfs-tools/modules
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have been loaded.
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.TP
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\fB\fI
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local-top OR nfs-top
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After these scripts have been executed, the root device node is expected to be
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present (local) or the network interface is expected to be usable (NFS).
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.TP
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\fB\fI
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local-premount OR nfs-premount
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are run after the sanity of the root device has been verified (local) or the
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network interface has been brought up (NFS), but before the actual root fs has
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been mounted.
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.TP
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\fB\fI
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local-bottom OR nfs-bottom
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are run after the rootfs has been mounted (local) or the NFS root share has
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been mounted. udev is stopped.
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.TP
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\fB\fI
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init-bottom
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are the last scripts to be executed before procfs and sysfs are moved to the
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real rootfs and execution is turned over to the init binary which should now be
|
||
|
|
found in the mounted rootfs.
|
||
|
|
|
||
|
|
.SS Boot parameters
|
||
|
|
.TP
|
||
|
|
\fB\fI
|
||
|
|
/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.
|
||
|
|
|
||
|
|
|
||
|
|
.SH EXAMPLES
|
||
|
|
|
||
|
|
.SS Hook script
|
||
|
|
An example hook script would look something like this (and would usually be
|
||
|
|
placed in /etc/initramfs-tools/hooks/frobnicate):
|
||
|
|
|
||
|
|
.RS
|
||
|
|
.nf
|
||
|
|
#!/bin/sh
|
||
|
|
# Example frobnication hook script
|
||
|
|
|
||
|
|
PREREQ="lvm"
|
||
|
|
prereqs()
|
||
|
|
{
|
||
|
|
echo "$PREREQ"
|
||
|
|
}
|
||
|
|
|
||
|
|
case $1 in
|
||
|
|
prereqs)
|
||
|
|
prereqs
|
||
|
|
exit 0
|
||
|
|
;;
|
||
|
|
esac
|
||
|
|
|
||
|
|
\fR. /usr/share/initramfs-tools/hook-functions
|
||
|
|
# Begin real processing below this line
|
||
|
|
|
||
|
|
if [ ! \-x "/sbin/frobnicate" ]; then
|
||
|
|
exit 0
|
||
|
|
fi
|
||
|
|
|
||
|
|
force_load frobnicator interval=10
|
||
|
|
cp /sbin/frobnicate "${DESTDIR}/sbin"
|
||
|
|
exit 0
|
||
|
|
.fi
|
||
|
|
.RE
|
||
|
|
|
||
|
|
.SS Boot script
|
||
|
|
An example boot script would look something like this (and would usually be placed in /etc/initramfs-tools/scripts/local-top/frobnicate):
|
||
|
|
|
||
|
|
.RS
|
||
|
|
.nf
|
||
|
|
#!/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
|
||
|
|
.fi
|
||
|
|
.RE
|
||
|
|
|
||
|
|
.SS Exported variables
|
||
|
|
init sets several variables for the boot scripts environment.
|
||
|
|
|
||
|
|
.TP
|
||
|
|
\fB\fI ROOT
|
||
|
|
correponds to the root boot option.
|
||
|
|
Advanced boot scripts like cryptsetup or live-initramfs need to play tricks.
|
||
|
|
Otherwise keep it alone.
|
||
|
|
.TP
|
||
|
|
\fB\fI ROOTDELAY, ROOTFLAGS, ROOTFSTYPE, IP
|
||
|
|
correponds to the rootdelay, rootflags, rootfstype or ip boot option.
|
||
|
|
.TP
|
||
|
|
\fB\fI DPKG_ARCH
|
||
|
|
allows arch specific boot actions.
|
||
|
|
.TP
|
||
|
|
\fB\fI blacklist, panic, quiet, resume, noresume, resume_offset
|
||
|
|
set according relevant boot option.
|
||
|
|
.TP
|
||
|
|
\fB\fI break
|
||
|
|
Useful for manual intervention during setup and coding an boot script.
|
||
|
|
.TP
|
||
|
|
\fB\fI init
|
||
|
|
passes the path to init(8) usually /sbin/init.
|
||
|
|
.TP
|
||
|
|
\fB\fI readonly
|
||
|
|
is the default for mounting the root corresponds to the ro bootarg.
|
||
|
|
Overriden by rw bootarg.
|
||
|
|
.TP
|
||
|
|
\fB\fI rootmnt
|
||
|
|
is the path where root gets mounted usualy /root.
|
||
|
|
.TP
|
||
|
|
\fB\fI debug
|
||
|
|
indicates that a debug log is captured for further investigation.
|
||
|
|
|
||
|
|
|
||
|
|
.SH 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:
|
||
|
|
.RS
|
||
|
|
.nf
|
||
|
|
mkdir tmp/initramfs
|
||
|
|
cd tmp/initramfs
|
||
|
|
gunzip \-c /boot/initrd.img\-2.6.18\-1\-686 | \\
|
||
|
|
cpio \-i \-d \-H newc \-\-no\-absolute\-filenames
|
||
|
|
.fi
|
||
|
|
.RE
|
||
|
|
|
||
|
|
|
||
|
|
.SH AUTHOR
|
||
|
|
The initramfs-tools are written by Maximilian Attems <maks@debian.org>,
|
||
|
|
Jeff Bailey <jbailey@raspberryginger.com> and numerous others.
|
||
|
|
.PP
|
||
|
|
This manual was written by David H\[:a]rdeman <david@hardeman.nu>,
|
||
|
|
updated by Maximilian Attems <maks@debian.org>.
|
||
|
|
|
||
|
|
.SH SEE ALSO
|
||
|
|
.BR
|
||
|
|
.IR initramfs.conf (5),
|
||
|
|
.IR mkinitramfs (8),
|
||
|
|
.IR update-initramfs(8).
|