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 filesystems and root filesystems 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

-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 filesystem 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.

-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, --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 isn’t 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’s happening during creation of the ramdisk.

-z, --compress compress

Override the compression method with the compress program.

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. Presets are located in /etc/mkinitcpio.d

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. Optionally, a destination within the initramfs image as well as a file mode can be specified. By default, the destintation 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. 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_dir path

Adds a directory and its parents to the image.

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 filesystem, and the target will be read using readlink. 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

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.

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.

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.

Specifies that root should be mounted with readonly permissions. This is the default behavior.

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 filesystem. Acceptable values are filesystem specific.

rootfstype=fstype

Overrides the type of filesystem 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.