NAME¶

DESCRIPTION¶

Kernel Command Line¶

Standard¶

init= "<path to real init>"

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

 

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.

 

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

On install initramfs-tools tries to autodetect the resume partition. 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,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 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.

 

netconsole

loads netconsole linux modules with the chosen args.

 

all_generic_ide

loads generic IDE/ATA chipset support on boot.

 

 

HOOK SCRIPTS¶

Hook scripts¶

Boot scripts¶

Header¶

#!/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

Help functions¶

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

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.

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.

copy_modules_dir copies an entire module directory from /lib/modules/KERNELVERSION/ into the initramfs image.

Including binaries¶

Exported variables¶

MODULESDIR

corresponds to the linux-2.6 modules dir.

version

is the $(uname -r) linux-2.6 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.

KEYMAP

sets if a keymap needs to be added to initramfs.

MODULES

specifies which kind of modules should land on initramfs. This setting shouldn't be overridden by hook script, but can guide them on how much they need to include on initramfs.

 

 

BOOT SCRIPTS¶

Header¶

#!/bin/sh
PREREQ=""
prereqs()
{
	echo "$PREREQ"
}

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

Help functions¶

log_success_msg Logs a success message

log_failure_msg Logs a failure message

log_warning_msg Logs a warning message

log_begin_msg Logs a message that some processing step has begun

 

log_end_msg Logs a message that some processing step is finished

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.

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-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¶

#!/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
cp /sbin/frobnicate "${DESTDIR}/sbin"
exit 0

Boot script¶

#!/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¶

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.

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.

 

 

DEBUG¶

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¶

SEE ALSO¶