MKINITCPIO(8) mkinitcpio manual MKINITCPIO(8)
NAME
mkinitcpio - Create an initial ramdisk environment
SYNOPSIS
mkinitcpio [options]
DESCRIPTION
Creates an initial ramdisk environment for booting the Linux kernel.
The initial ramdisk is in essence a very small environment (early
userspace) which loads various kernel modules and sets up necessary
things before handing over control to init. This makes it possible to
have, for example, encrypted root file systems and root file systems on
a software RAID array. mkinitcpio allows for easy extension with custom
hooks, has autodetection at runtime, and many other features.
OPTIONS
-A, --addhooks hooks
Add the additional hooks to the image. These will be processed in
order after all other hooks from the config file. Multiple hooks
should be comma-separated. This option can be specified multiple
times.
-c, --config config
Use config file to generate the ramdisk. Default:
/etc/mkinitcpio.conf. If specified, drop-in files in
/etc/mkinitcpio.conf.d/ will be ignored.
-d, --generatedir directory
Set directory as the location where the initramfs is built. This
might be useful to generate a shutdown ramfs in /run/initramfs/.
-D, --hookdir directory
Set directory as the location where hooks will be searched for when
generating the image.
-g, --generate filename
Generate a CPIO image as filename. Default: no; this means nothing
will be written to the file system unless this option is specified.
-H, --hookhelp hookname
Output help for hookname hookname.
-h, --help
Output a short overview of available command-line switches.
-k, --kernel kernelversion
Use kernelversion, instead of the current running kernel. This may
be a path to a kernel image (only supported for x86-based
architectures), a specific kernel version or the special keyword
none. In the latter case, no kernel modules are added to the image.
-L, --listhooks
List all available hooks.
-M, --automods
Display modules found via autodetection. mkinitcpio will
automatically try to determine which kernel modules are needed to
start your computer. This option lists which modules were detected.
-n, --nocolor
Disable color output.
-U, --uki filename
Generate a unified kernel image as filename. If a CPIO image is
successfully built, it will be used to generate a unified kernel
image for UEFI booting. This combines the initramfs, the kernel,
and the kernel cmdline into one executable. This is useful for boot
chain integrity where the file is signed. Default: no. For a list
of relevant options see Options for unified kernel image below.
-P, --allpresets
Process all presets contained in /etc/mkinitcpio.d. See the -p
option for more detail about presets.
-p, --preset preset
Build initramfs image(s) according to specified preset. This may be
a file in /etc/mkinitcpio.d (without the .preset extension) or a
full, absolute path to a file. This option may be specified
multiple times to process multiple presets.
-R, --remove
Remove initramfs image(s) generated by the specified preset(s). If
used in combination with -P|--allpresets, removes the images for
all presets. This option can only be used with either -p|--presets
or -P|--allpresets.
-r, --moduleroot root
Specifies the root directory to find modules in, defaulting to /.
-S, --skiphooks hooks
Skip hooks when generating the image. Multiple hooks should be
comma-separated. This option can be specified multiple times.
-s, --save
Saves the build directory for the initial ramdisk. Default: no;
This means the directory will not be retained if this option is not
specified. Useful for debugging purposes.
-t, --builddir tmpdir
Use tmpdir as the temporary build directory instead of /tmp. tmpdir
must exist. The TMPDIR environment variable is also honored to set
this location, but the command line option will take precedence.
-V, --version
Display version information.
-v, --verbose
Verbose output. Outputs more information about what is happening
during creation of the ramdisk.
-z, --compress compress
Override the compression method with the compress program.
OPTIONS FOR UNIFIED KERNEL IMAGE
--cmdline filename
Use kernel command line with unified kernel image. If none is
specified, try one of the files /etc/kernel/cmdline,
/usr/lib/kernel/cmdline or /proc/cmdline.
--no-cmdline
Omit embedding a kernel command line string in the unified kernel
image. Kernel command line options will need to be passed via the
kernel command line. Overrides the --cmdline option.
--splash filename
UEFI executables can show a bitmap file on boot.
--uefistub filename
UEFI stub image used for unified kernel image generation. Has no
effect if ukify is being used. Default: Attempts to look for a
systemd-boot or gummiboot stub loader.
--ukiconfig filename
Configuration file to pass to ukify. If none is specified, try one
of the files /etc/kernel/uki.conf or /usr/lib/kernel/uki.conf. If
neither of those exists, ukify will use its internal default.
--no-ukify
Do not use ukify to build UKIs even if it is available. This is not
recommended.
--kernelimage filename
Include a kernel image for the unified kernel image. Default: one
of /lib/modules/${KERNELVERSION}/vmlinuz,
/boot/vmlinuz-${KERNELVERSION}, or /boot/vmlinuz-linux.
--osrelease filename
Include a os-release file for the unified kernel image. Default:
/etc/os-release or /usr/lib/os-release.
ABOUT PRESETS
A preset is a pre-defined definition on how to create an initial
ramdisk. Instead of specifying the configuration file and which output
file, every time you generate a new initial ramdisk, you define a
preset and use the -p switch to generate an initial ramdisk according
to your preset.
Typically, presets are files located in /etc/mkinitcpio.d/ with the
extension .preset, e.g. /etc/mkinitcpio.d/linux.preset for the linux
preset. It is possible to use files in other locations, too. Then the
path to this file needs to be specified.
Presets files are shell scripts that get sourced by mkinitcpio and the
following variables will influence its behavior.
Note, that mkinitcpio calls itself for each preset and passes the
options defined in the preset file file via command line arguments.
Those are mentioned in the description of the options below, so refer
to the manual of the command line arguments for more information about
a particular option.
PRESETS
An array of preset names defined in this file. These names will be
used as prefix to other options to provide preset-specific options.
For example, if a PRESET=('custom') is given, then the image is
specified via custom_image='/boot/custom.img'.
<preset>_kver (defaults to value of ALL_kver ā one of the two is
required)
Specify the Kernel version (via -k in mkinitcpio).
<preset>_config (defaults to value of ALL_config ā one of the two is
required)
Path to the configuration file (passed via -c to mkinitcpio).
<preset>_uki (one of <preset>_uki and <preset>_image is required)
Output file path for a unified kernel image (passed via -U to
mkinitcpio).
<preset>_image (one of <preset>_uki and <preset>_image is required)
Output file path for the generated image (passed via -g to
mkinitcpio).
<preset>_options
Further command line arguments to pass to mkinitcpio as a string or
array. They will get appended at the end of the call to mkinitcpio
(after all the options mentioned above), so this can be used to
overwrite options (for example pass a -S hook here to skip a hook).
ABOUT INSTALL HOOKS
Install hooks are bash scripts which are sourced during mkinitcpio
runtime in order to add modules, binaries, and other files to the
image. A variety of functions exist to facilitate this.
add_module modname
Adds the module specified by modname to the image. Dependencies are
derived and added automatically.
add_binary binary [ destination ] [ mode ]
Adds a binary to the image. The argument binary need not be an
absolute path and, if needed, a lookup will be performed. If the
binary is a dynamically linked ELF binary, dependencies will be
automatically added. If it is a symlink, both the symlink and the
target binary will be added. Optionally, a destination within the
initramfs image as well as a file mode can be specified. By
default, the destination and mode be taken from the source derived
from binary.
add_file path [ destination ] [ mode ]
Adds a file and any needed parent directories to the image. If it
is a symlink, both the symlink and the target file will be added.
Optionally, a destination within the initramfs image as well as a
file mode can be specified. By default, the destination and mode
will be taken from the source and mode of the file specified by the
path.
add_file_early path [ destination ] [ mode ]
Adds a file and any needed parent directories to the early
uncompressed image. Works the same way as add_file.
add_dir path
Adds a directory and its parents to the image.
add_dir_early path
Adds a directory and its parents to the early uncompressed image.
Works the same way as add_dir.
add_full_dir directory [ glob ] [ strip_prefix ]
Recursively adds a directory to the image by walking the given path
and calling add_file, add_dir, and add_symlink accordingly. This
function will not follow symlinks, nor will it add the targets of
symlinks.
If the glob argument is passed, only files and symlinks matching
this glob will be added.
If the strip_prefix argument is passed, it will be used to strip
the destination path (path in the initramfs image) from the prefix
specified by the strip_prefix argument. This can be useful when
writing rootfs-overlay hooks.
add_symlink path [ link-target ]
Adds a symlink to the image at the specified path, optionally
pointing to the specified link-target. If the link-target is not
provided, it is assumed that this symlink exists in the real file
system, and the target will be read using readlink(1). There is no
checking done to ensure that the target of the symlink exists, and
symlinks will not be followed recursively.
add_all_modules [ -f filter ] pattern
Adds modules to the image, without regard for the autodetect
whitelist. pattern should be a subdirectory within the kernel tree
describing a subset of modules to be included. Further refinement
can be provided via the -f flag with an extended regular
expression.
add_checked_modules [ -f filter ] pattern
Similar to add_all_modules with the constraint that only modules
matching the whitelist generated by the autodetect hook will be
added to the image. If the autodetect hook is not present in the
image, this function is identical to add_all_modules.
add_runscript scriptname
Adds a runtime hook to the image, which is a busybox ash compatible
shell script. The name of the script is guaranteed to match the
name of the hook the script is called from.
add_udev_rule rule-file
Adds a udev rule to the image. Dependencies on binaries will be
discovered and added. The argument can be a rule file name
(discovered from well known udev paths) or an absolute path.
add_all_modules_from_symbol symbol paths
Adds modules from the paths directories containing the symbol to
the image.
add_checked_modules_from_symbol symbol paths
Similar to add_all_modules_from_symbol with the constraint that
only modules matching the whitelist generated by the autodetect
hook will be added to the image. If the autodetect hook is not
present in the image, this function is identical to
add_all_modules_from_symbol.
ABOUT EARLY CPIO
mkinitcpio has support for early CPIO. These are uncompressed CPIO
archives prepended to the main compressed CPIO archive. They are used
for early loading CPU microcode or loading ACPI table overrides.
Install hooks can install files to this archive by adding them to
$EARLYROOT.
ABOUT RUNTIME HOOKS
Runtime hooks added to the image via the add_runscript function from an
install hook are able to provide extra functionality during early
userspace. Specific functions in these files will run at different
times. A hook can define one or more of these. At each hook point,
hooks are run in the order that they are defined in the HOOKS variable,
except for cleanup hooks which are run in reverse.
run_earlyhook
Functions of this name will be run once the API mounts have been
setup and the kernel command line has been parsed. Daemons needed
for early userspace should be started from this hook point.
run_hook
Functions of this name will be run after any early hooks, and after
user defined modules have been installed. This is the most common
hook point, and functionality such as scanning for LVM volumes and
mapping encrypted volumes should be performed here.
run_latehook
Functions of this name will be run after root has been mounted.
This is generally used for further necessary setup in the real
root, such as mounting other system partitions.
run_cleanuphook
Functions of this name are run as late as possible. Any daemons
started from a run_earlyhook function should be shut down here in
preparation for switching to the real root.
run_emergencyhook
Functions of this name are run before the emergency shell launched
in case of boot failure. For example this allows boot splash
screens to terminate their process, so users will notice the
failure.
getarg argument [ default ]
This function can be used in runtime hooks to get an argument from
the kernel cmdline. If argument exists with a value, the value is
returned. If argument exists without a value, y is returned. If
argument does not exist, default is returned. If default is not
specified, nothing is returned.
ABOUT POST HOOKS
Post hooks are executables or scripts that get executed after the image
has been successfully generated and can be used for further processing
(i.e. signing). They receive the kernel as the first argument, the
image as second and optionally the unified kernel image as a third.
Note that the first argument will be empty when the mkinitcpio has been
invoked with -k none or -k version and the kernel image cannot be found
on the file system.
The following enviroment variables are passed:
KERNELVERSION
Contains the full version of the kernel the image has been built
from.
KERNELDESTINATION
The default location where the kernel should be located for
booting. This usually is the same as the first argument but might
differ if mkinitcpio has not been invoked with -k /boot/*. If no
kernel image has been found this variable will be empty as well.
EARLY INIT ENVIRONMENT
mkinitcpio gives special treatment to certain environment variables
passed on the kernel command line:
break[=<premount|postmount>]
If specified, mkinitcpio will start a shell during early init. The
optional parameter controls when this occurs: when premount or no
parameter are specified, the shell will be launched prior to
mounting root. If postmount is specified, the shell will be
launched after mounting root.
disablehooks=hooklist
This is a comma separated list of hooks which will be skipped
during early init.
earlymodules=modulelist
This is a comma separated list of modules which will be loaded
prior to any others. This is generally not needed, and usually
points to a configuration or kernel problem.
quiet
Causes mkinitcpio to output fewer messages during boot. Errors will
not be suppressed.
ro
Specifies that root should be mounted with readonly permissions.
This is the default behavior.
rw
Specifies that root should be mounted with readwrite permissions.
This is generally only useful if your initramfs uses the fsck hook.
root=rootdevice
This variable describes the root partition which early init will
mount before passing control to the real init. mkinitcpio
understands a variety of formats, the most basic of which is the
path to the block device, either directly such as /dev/sda2, or
using a udev symlink such as /dev/disk/by-label/CorsairF80-root.
Support for identification by LABEL or UUID tags are also
supported, such as, LABEL=CorsairF80-root. As of util-linux 2.22,
PARTUUID and PARTLABEL are also supported. Identification via hex
encoded major/minor device ID is supported for legacy reasons, but
should be avoided as it tends to be fragile.
rootdelay[=seconds]
Sets the delay, in seconds, that mkinitcpio is willing to wait for
the root device to show up, if it is not available immediately.
This defaults to 10 seconds. If an invalid integer is passed, this
variable will have no effect.
rootflags=flaglist
A comma-separated list of flags which will be passed onto the
mount(8) command when mounting the root file system. Acceptable
values are file system specific.
rootfstype=fstype
Overrides the type of file system being mounted as root. This
should almost never be needed as mount(8) usually detects this on
its own.
rd.debug
Enables shell debug (xtrace). If rd.log is not also a parameter on
the kernel command line, this parameter implies rd.log=console.
rd.log[=<console|file|kmsg|all>]
Enables logging of early userspace messages. If specified, the
optional parameter describes where this information is logged.
Multiple options can be OR-d together using the pipe (|) character.
Messages are always logged to the console unless the quiet
parameter is passed. If the optional parameter is not specified,
kmsg|console is assumed. If rd.log is not present on the kernel
command line, no logging will take place.
console
Writes output to /dev/console.
file
Writes output to /run/initramfs/init.log.
kmsg
Writes output to the /dev/kmsg device (introduced in Linux
3.5). This option is a no-op if your kernel lacks support for
/dev/kmsg.
all
Writes output to all known log targets.
These are only the variables that the core of mkinitcpio honor.
Additional hooks may look for other environment variables and should be
documented by the help output for the hook.
REPRODUCIBILITY
mkinitcpio aims to create reproducible initramfs images by default.
This means that two subsequent runs of mkinitcpio should produce two
files that are identical at the binary level.
Timestamps within the initramfs are set to the Unix epoch of
1970-01-01.
Note that in order for the build to be fully reproducible, the
compressor specified (e.g. gzip, xz) must also produce reproducible
archives. At the time of writing, as an inexhaustive example, the lzop
compressor is incapable of producing reproducible archives due to the
insertion of a runtime timestamp.
More information can be found at <https://reproducible-builds.org>.
FILES
/etc/mkinitcpio.conf
Default configuration file for mkinitcpio.
/etc/mkinitcpio.conf.d
Directory containing drop-in configuration files.
/etc/mkinitcpio.d
Directory containing mkinitcpio presets.
/etc/initcpio/install, /usr/lib/initcpio/install
Search path for build time hooks.
/etc/initcpio/hooks, /usr/lib/initcpio/hooks
Search path for early userspace runtime hooks.
/etc/initcpio/post, /usr/lib/initcpio/post
Search path for post generation hooks.
EXAMPLES
mkinitcpio
Perform a dry-run. This will generate an initial ramdisk but will
not write anything. Use -g to create the real image.
mkinitcpio -p linux
Create an initial ramdisk based on the linux preset.
mkinitcpio -g /boot/initramfs-linux.img -k /boot/vmlinuz-linux
Create an initial ramdisk for the kernel at /boot/vmlinuz-linux.
The resulting image will be written to /boot/initramfs-linux.img.
mkinitcpio -U /efi/EFI/Linux/systemd-linux.efi
Create an initial ramdisk for the kernel along with a unified
kernel image. The resulting executable will be written to
/efi/EFI/Linux/systemd-linux.efi.
mkinitcpio -U /efi/EFI/Linux/systemd-linux.efi --splash
/usr/share/systemd/bootctl/splash-arch.bmp
Create an initial ramdisk for the kernel and a unified kernel
image. This also includes a splash image which will be used during
boot.
SEE ALSO
A more thorough article on configuring mkinitcpio:
<https://wiki.archlinux.org/title/mkinitcpio>
initrd(4), lsinitcpio(1), mkinitcpio.conf(5), bootparam(7)
BUGS
Upon writing this man page, there were no noticeable bugs present.
Please visit
<https://gitlab.archlinux.org/archlinux/mkinitcpio/mkinitcpio/-/issues>
for an up to date list.
AUTHORS
mkinitcpio is maintained by the Arch Linux community. Refer to the
AUTHORS file for a full list of contributors.
COPYRIGHT
Copyright šÆ mkinitcpio contributors. GPL-2.0-only.
Ā 2024-04-27 MKINITCPIO(8)
mkinitcpio \- Create an initial ramdisk environment