NAME

       kernel-install - Add and remove kernel and initrd images to and from /boot

SYNOPSIS

       kernel-install [OPTIONS...] COMMAND KERNEL-VERSION KERNEL-IMAGE [INITRD-FILE...]

DESCRIPTION

       kernel-install is used to install and remove kernel and initrd images [1] to and from the
       boot loader partition, referred to as $BOOT here. It will usually be one of /boot/, /efi/,
       or /boot/efi/, see below.

       kernel-install will run the executable files ("plugins") located in the directory
       /usr/lib/kernel/install.d/ and the local administration directory /etc/kernel/install.d/.
       All files are collectively sorted and executed in lexical order, regardless of the
       directory in which they live. However, files with identical filenames replace each other.
       Files in /etc/kernel/install.d/ take precedence over files with the same name in
       /usr/lib/kernel/install.d/. This can be used to override a system-supplied executables
       with a local file if needed; a symbolic link in /etc/kernel/install.d/ with the same name
       as an executable in /usr/lib/kernel/install.d/, pointing to /dev/null, disables the
       executable entirely. Executables must have the extension ".install"; other extensions are
       ignored.

       An executable placed in these directories should return 0 on success. It may also return
       77 to cause the whole operation to terminate (executables later in lexical order will be
       skipped).

COMMANDS

       The following commands are understood:

       add KERNEL-VERSION KERNEL-IMAGE [INITRD-FILE ...]
           This command expects a kernel version string and a path to a kernel image file as
           arguments. Optionally, one or more initrd images may be specified as well (note that
           plugins might generate additional ones).  kernel-install calls the executable files
           from /usr/lib/kernel/install.d/*.install and /etc/kernel/install.d/*.install (i.e. the
           plugins) with the following arguments:

               add KERNEL-VERSION $BOOT/ENTRY-TOKEN/KERNEL-VERSION/ KERNEL-IMAGE [INITRD-FILE ...]

           The third argument directly refers to the path where to place kernel images, initrd
           images and other resources for Boot Loader Specification[2] Type #1 entries (the
           "entry directory"). If other boot loader schemes are used the parameter may be
           ignored. The ENTRY-TOKEN string is typically the machine ID and is supposed to
           identify the local installation on the system. For details see below.

           Two default plugins execute the following operations in this case:

           •   kernel-install creates $BOOT/ENTRY-TOKEN/KERNEL-VERSION, if enabled (see
               $KERNEL_INSTALL_LAYOUT).

           •   50-depmod.install runs depmod(8) for the KERNEL-VERSION.

           •   90-loaderentry.install copies KERNEL-IMAGE to
               $BOOT/ENTRY-TOKEN/KERNEL-VERSION/linux. If INITRD-FILEs are provided, it also
               copies them to $BOOT/ENTRY-TOKEN/KERNEL_VERSION/INITRD-FILE. It also creates a
               boot loader entry according to the Boot Loader Specification[2] (Type #1) in
               $BOOT/loader/entries/ENTRY-TOKEN-KERNEL-VERSION.conf. The title of the entry is
               the PRETTY_NAME parameter specified in /etc/os-release or /usr/lib/os-release (if
               the former is missing), or "Linux KERNEL-VERSION", if unset.

               If $KERNEL_INSTALL_LAYOUT is not "bls", this plugin does nothing.

           •   90-uki-copy.install copies a file uki.efi from $KERNEL_INSTALL_STAGING_AREA or if
               it does not exist the KERNEL-IMAGE argument, iff it has a ".efi" extension, to
               $BOOT/EFI/Linux/ENTRY-TOKEN-KERNEL-VERSION.efi.

               If $KERNEL_INSTALL_LAYOUT is not "uki", this plugin does nothing.

       remove KERNEL-VERSION
           This command expects a kernel version string as single argument. This calls
           executables from /usr/lib/kernel/install.d/*.install and
           /etc/kernel/install.d/*.install with the following arguments:

               remove KERNEL-VERSION $BOOT/ENTRY-TOKEN/KERNEL-VERSION/

           Afterwards, kernel-install removes the entry directory
           $BOOT/ENTRY-TOKEN/KERNEL-VERSION/ and its contents, if it exists.

           Two default plugins execute the following operations in this case:

           •   50-depmod.install removes the files generated by depmod for this kernel again.

           •   90-loaderentry.install removes the file
               $BOOT/loader/entries/ENTRY-TOKEN-KERNEL-VERSION.conf.

           •   90-uki-copy.install removes the file
               $BOOT/EFI/Linux/ENTRY-TOKEN-KERNEL-VERSION.efi.

       inspect
           Shows the various paths and parameters configured or auto-detected. In particular
           shows the values of the various $KERNEL_INSTALL_* environment variables listed below.

THE $BOOT PARTITION

       The partition where the kernels and Boot Loader Specification[2] snippets are located is
       called $BOOT.  kernel-install determines the location of this partition by checking /efi/,
       /boot/, and /boot/efi/ in turn. The first location where $BOOT/loader/entries/ or
       $BOOT/ENTRY-TOKEN/ exists is used.

OPTIONS

       The following options are understood:

       -v, --verbose
           Output additional information about operations being performed.

       -h, --help
           Print a short help text and exit.

       --version
           Print a short version string and exit.

ENVIRONMENT VARIABLES

   Environment variables exported for plugins
       If --verbose is used, $KERNEL_INSTALL_VERBOSE=1 will be exported for plugins. They may
       output additional logs in this case.

       $KERNEL_INSTALL_MACHINE_ID is set for the plugins to the desired machine-id to use. It's
       always a 128-bit ID. Normally it's read from /etc/machine-id, but it can also be
       overridden via $MACHINE_ID (see below). If not specified via these methods, a fallback
       value will generated by kernel-install and used only for a single invocation.

       $KERNEL_INSTALL_ENTRY_TOKEN is set for the plugins to the desired entry "token" to use.
       It's an identifier that shall be used to identify the local installation, and is often the
       machine ID, i.e. same as $KERNEL_INSTALL_MACHINE_ID, but might also be a different type of
       identifier, for example a fixed string or the ID=, IMAGE_ID= values from /etc/os-release.
       The string passed here will be used to name Boot Loader Specification entries, or the
       directories the kernel image and initial RAM disk images are placed into.

       Note that while $KERNEL_INSTALL_ENTRY_TOKEN and $KERNEL_INSTALL_MACHINE_ID are often set
       to the same value, the latter is guaranteed to be a valid 32 character ID in lowercase
       hexadecimals while the former can be any short string. The entry token to use is read from
       /etc/kernel/entry-token, if it exists. Otherwise a few possible candidates below $BOOT are
       checked for Boot Loader Specification Type 1 entry directories, and if found the entry
       token is derived from that. If that is not successful, $KERNEL_INSTALL_MACHINE_ID is used
       as fallback.

       $KERNEL_INSTALL_BOOT_ROOT is set for the plugins to the absolute path of the root
       directory (mount point, usually) of the hierarchy where boot loader entries, kernel
       images, and associated resources should be placed. This usually is the path where the
       XBOOTLDR partition or the ESP (EFI System Partition) are mounted, and also conceptually
       referred to as $BOOT. Can be overridden by setting $BOOT_ROOT (see below).

       $KERNEL_INSTALL_LAYOUT=bls|uki|other|...  is set for the plugins to specify the
       installation layout. Defaults to bls if $BOOT/ENTRY-TOKEN exists, or other otherwise.
       Additional layout names may be defined by convention. If a plugin uses a special layout,
       it's encouraged to declare its own layout name and configure layout= in install.conf upon
       initial installation. The following values are currently understood:

       bls
           Standard Boot Loader Specification[2] Type #1 layout, compatible with systemd-boot(7):
           entries in $BOOT/loader/entries/ENTRY-TOKEN-KERNEL-VERSION[+TRIES].conf, kernel and
           initrds under $BOOT/ENTRY-TOKEN/KERNEL-VERSION/

           Implemented by 90-loaderentry.install.

       uki
           Standard Boot Loader Specification[2] Type #2 layout, compatible with systemd-boot(7):
           unified kernel images under $BOOT/EFI/Linux as
           $BOOT/EFI/Linux/ENTRY-TOKEN-KERNEL-VERSION[+TRIES].efi.

           Implemented by 90-uki-copy.install.

       other
           Some other layout not understood natively by kernel-install.

       $KERNEL_INSTALL_INITRD_GENERATOR is set for plugins to select the initrd generator. This
       may be configured as initrd_generator= in install.conf, see below.

       $KERNEL_INSTALL_STAGING_AREA is set for plugins to a path to a directory. Plugins may drop
       files in that directory, and they will be installed as part of the loader entry, based on
       the file name and extension.

   Environment variables understood by kernel-install
       $KERNEL_INSTALL_CONF_ROOT can be set to override the location of the configuration files
       read by kernel-install. When set, install.conf, entry-token, and other files will be read
       from this directory.

       $KERNEL_INSTALL_PLUGINS can be set to override the list of plugins executed by
       kernel-install. The argument is a whitespace-separated list of paths.
       "KERNEL_INSTALL_PLUGINS=:" may be used to prevent any plugins from running.

       $MACHINE_ID can be set for kernel-install to override $KERNEL_INSTALL_MACHINE_ID, the
       machine ID.

       $BOOT_ROOT can be set for kernel-install to override $KERNEL_INSTALL_BOOT_ROOT, the
       installation location for boot entries.

       The last two variables may also be set in install.conf. Variables set in the environment
       take precedence over the values specified in the config file.

EXIT STATUS

       If every executable returns 0 or 77, 0 is returned, and a non-zero failure code otherwise.

FILES

       /usr/lib/kernel/install.d/*.install /etc/kernel/install.d/*.install
           Drop-in files which are executed by kernel-install.

       /usr/lib/kernel/cmdline /etc/kernel/cmdline /proc/cmdline
           Read by 90-loaderentry.install. The content of the file /etc/kernel/cmdline specifies
           the kernel command line to use. If that file does not exist, /usr/lib/kernel/cmdline
           is used. If that also does not exist, /proc/cmdline is used.
           $KERNEL_INSTALL_CONF_ROOT may be used to override the path.

       /etc/kernel/tries
           Read by 90-loaderentry.install and 90-uki-copy.install. If this file exists a numeric
           value is read from it and the naming of the generated entry file or UKI is slightly
           altered to include it as $BOOT/loader/entries/ENTRY-TOKEN-KERNEL-VERSION+TRIES.conf or
           $BOOT/EFI/Linux/ENTRY-TOKEN-KERNEL-VERSION+TRIES.efi, respectively. This is useful for
           boot loaders such as systemd-boot(7) which implement boot attempt counting with a
           counter embedded in the entry file name.  $KERNEL_INSTALL_CONF_ROOT may be used to
           override the path.

       /etc/kernel/entry-token
           If this file exists it is read and used as "entry token" for this system, i.e. is used
           for naming Boot Loader Specification entries, see $KERNEL_INSTALL_ENTRY_TOKEN above
           for details.  $KERNEL_INSTALL_CONF_ROOT may be used to override the path.

       /etc/machine-id
           The content of this file specifies the machine identification MACHINE-ID.

       /etc/os-release /usr/lib/os-release
           Read by 90-loaderentry.install. If available, PRETTY_NAME= is read from these files
           and used as the title of the boot menu entry. Otherwise, "Linux KERNEL-VERSION" will
           be used.

       /usr/lib/kernel/install.conf /etc/kernel/install.conf
           Configuration options for kernel-install, as a series of KEY=VALUE assignments,
           compatible with shell syntax, following the same rules as described in os-release(5).
           /etc/kernel/install.conf will be read if present, and /usr/lib/kernel/install.conf
           otherwise. This file is optional.  $KERNEL_INSTALL_CONF_ROOT may be used to override
           the path.

           Currently, the following keys are supported: MACHINE_ID=, BOOT_ROOT=, layout=,
           initrd_generator=. See the Environment variables section above for details.

SEE ALSO

       machine-id(5), os-release(5), depmod(8), systemd-boot(7), Boot Loader Specification[2]

NOTES

        1. Nowadays actually CPIO archives used as an "initramfs", rather than "initrd". See
           bootup(7) for an explanation.

        2. Boot Loader Specification
           https://uapi-group.org/specifications/specs/boot_loader_specification