man > kernel-install(8)

KERNEL-INSTALL(8)                          kernel-install                          KERNEL-INSTALL(8)

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

SYNOPSIS


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

       kernel-install [OPTIONS...] remove KERNEL-VERSION

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

       kernel-install [OPTIONS...] list

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 takes a kernel version string and a path to a kernel image file as
           arguments. If the former is omitted, specified as an empty string or as "-" it defaults
           to the current kernel version, i.e. the same string uname -r returns. If the latter is
           omitted, specified as an empty string or as "-" defaults to
           /usr/lib/modules/KERNEL_VERSION/vmlinuz. Optionally, one or more initrd images may be
           specified as well (note that plugins might generate additional ones).

           The executable files from /usr/lib/kernel/install.d/*.install and
           /etc/kernel/install.d/*.install (i.e. the plugins) are called 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. This can also be used to prepend
               microcode before the actual initrd. 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, only if 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.

           Added in version 198.

       add-all
           This is the same as add (see above), but invokes the operation iteratively for every
           installed kernel in /usr/lib/modules/. This operation is only supported on systems where
           the kernel image is installed in /usr/lib/modules/KERNEL-VERSION/vmlinuz.

           Added in version 255.

       remove KERNEL-VERSION
           This command expects a kernel version string as single argument.

           The executable files from /usr/lib/kernel/install.d/*.install and
           /etc/kernel/install.d/*.install (i.e. the plugins) are called 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.

           Added in version 198.

       inspect [[[KERNEL-VERSION] KERNEL-IMAGE] [INITRD-FILE ...]]
           Takes the same parameters as add.

           Shows the various paths and parameters configured or auto-detected. In particular shows
           the values of the various $KERNEL_INSTALL_* environment variables listed below, as they
           would be passed to plugins. The --json option can be used to get the output of this verb
           as a JSON object.

           Added in version 251.

       list
           Shows the various installed kernels. This enumerates the subdirectories of
           /usr/lib/modules/, and shows whether a kernel image is installed there.

           Added in version 255.

COMPATIBILITY WITH THE KERNEL BUILD SYSTEM


       installkernel [OPTIONS...] VERSION VMLINUZ [MAP] [INSTALLATION-DIR]

       When invoked as installkernel, this program accepts arguments as specified by the kernel
       build system's make install command. The VERSION and VMLINUZ parameters specify the kernel
       version and the kernel binary. The other two parameters (MAP and INSTALLATION-DIR) are
       currently ignored.

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:

       --esp-path=
           Path to the EFI System Partition (ESP). If not specified, /efi/, /boot/, and /boot/efi/
           are checked in turn. It is recommended to mount the ESP to /efi/, if possible.

       --boot-path=
           Path to the Extended Boot Loader partition, as defined in the Boot Loader
           Specification[2]. If not specified, /boot/ is checked. It is recommended to mount the
           Extended Boot Loader partition to /boot/, if possible.

       --make-entry-directory=yes|no|auto
           Controls creation and deletion of the Boot Loader Specification[2] Type #1 entry
           directory on the file system containing resources such as kernel and initrd images during
           add and remove, respectively. The directory is named after the entry token, and is placed
           immediately below the boot root directory. When "auto", the directory is created or
           removed only when the install layout is "bls". Defaults to "auto".

           Added in version 254.

       --entry-token=
           Controls how to name and identify boot loader entries for this kernel installation or
           deletion. Takes one of "auto", "machine-id", "os-id", "os-image-id", or an arbitrary
           string prefixed by "literal:" as argument.

           If set to machine-id the entries are named after the machine ID of the running system
           (e.g.  "b0e793a9baf14b5fa13ecbe84ff637ac"). See machine-id(5) for details about the
           machine ID concept and file.

           If set to os-id the entries are named after the OS ID of the running system, i.e. the ID=
           field of os-release(5) (e.g.  "fedora"). Similarly, if set to os-image-id the entries are
           named after the OS image ID of the running system, i.e. the IMAGE_ID= field of os-release
           (e.g.  "vendorx-cashier-system").

           If set to auto (the default), the /etc/kernel/entry-token (or
           $KERNEL_INSTALL_CONF_ROOT/entry-token) file will be read if it exists, and the stored
           value used. Otherwise if the local machine ID is initialized it is used. Otherwise
           IMAGE_ID= from os-release will be used, if set. Otherwise, ID= from os-release will be
           used, if set. Otherwise a randomly generated machine ID is used.

           Using the machine ID for naming the entries is generally preferable, however there are
           cases where using the other identifiers is a good option. Specifically: if the
           identification data that the machine ID entails shall not be stored on the (unencrypted)
           $BOOT_ROOT partition, or if the ID shall be generated on first boot and is not known when
           the entries are prepared. Note that using the machine ID has the benefit that multiple
           parallel installations of the same OS can coexist on the same medium, and they can update
           their boot loader entries independently. When using another identifier (such as the OS ID
           or the OS image ID), parallel installations of the same OS would try to use the same
           entry name. To support parallel installations, the installer must use a different entry
           token when adding a second installation.

           Added in version 254.

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

           Added in version 242.

       --root=root
           Takes a directory path as an argument. All paths will be prefixed with the given
           alternate root path, including config search paths. This is useful to operate on a system
           image mounted to the specified directory instead of the host system itself.

           Added in version 255.

       --image=image
           Takes a path to a disk image file or block device node. If specified, all operations are
           applied to the file system in the indicated disk image. This option is similar to
           --root=, but operates on file systems stored in disk images or block devices. The disk
           image should either contain just a file system or a set of file systems within a GPT
           partition table, following the Discoverable Partitions Specification[3]. For further
           information on supported disk images, see systemd-nspawn(1)'s switch of the same name.

           Added in version 255.

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

       --version
           Print a short version string and exit.

       --no-pager
           Do not pipe output into a pager.

       --json=MODE
           Shows output formatted as JSON. Expects one of "short" (for the shortest possible output
           without any redundant whitespace or line breaks), "pretty" (for a pretty version of the
           same, with indentation and line breaks) or "off" (to turn off JSON output, the default).

       --image-policy=policy
           Takes an image policy string as argument, as per systemd.image-policy(7). The policy is
           enforced when operating on the disk image specified via --image=, see above. If not
           specified defaults to the "*" policy, i.e. all recognized file systems in the image are
           used.

       --no-legend
           Do not print the legend, i.e. column headers and the footer with hints.

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_IMAGE_TYPE=uki|pe|unknown is set for the plugins to specify the type of the
       kernel image.

       uki
           Unified kernel image.

           Added in version 254.

       pe
           PE binary.

           Added in version 254.

       unknown
           Unknown type.

           Added in version 254.

       $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=auto|bls|uki|other|...  is set for the plugins to specify the
       installation layout. 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.

           Added in version 250.

       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.

           Added in version 253.

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

           Added in version 250.

       auto
           Pick the layout automatically. If the kernel is a UKI set layout to uki. If not default
           to bls if $BOOT/loader/entries.srel with content "type1" or $BOOT/ENTRY-TOKEN exists, or
           other otherwise.

           Leaving layout blank has the same effect. This is the default.

           Added in version 254.

       $KERNEL_INSTALL_INITRD_GENERATOR and $KERNEL_INSTALL_UKI_GENERATOR are set for plugins to
       select the initrd and/or UKI generator. This may be configured as initrd_generator= and
       uki_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: Files named initrd* will be installed as INITRD-FILEs, and files
       named microcode* will be prepended before INITRD-FILEs.

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

           Added in version 198.

       /etc/kernel/cmdline, /usr/lib/kernel/cmdline, /proc/cmdline
           Specifies the kernel command line to use. The first of the files that is found will be
           used.  $KERNEL_INSTALL_CONF_ROOT may be used to override the search path; see below for
           details.

           Added in version 198.

       /etc/kernel/devicetree, /usr/lib/kernel/devicetree
           Specifies the partial path to the file containing the device tree blob to install with
           the kernel and use at boot. The first of the files that is found will be used.
           $KERNEL_INSTALL_CONF_ROOT may be used to override the search path; see below for details.

           The devicetree file contains a path, and this path specifies a location relative to the
           kernel install tree. A set of locations is checked, including in particular
           /usr/lib/modules/KERNEL_VERSION/dtb/, which is the recommended location to place the dtb
           files under. For example, with "broadcom/bcm2711-rpi-4-b.dtb" in the devicetree file, the
           device tree blob for the Raspberry Pi 4 Model B would be installed, and the actual file
           would be /usr/lib/modules/KERNEL_VERSION/dtb/broadcom/bcm2711-rpi-4-b.dtb.

           Added in version 255.

       /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 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
           search path; see below for details.

           Added in version 240.

       /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 search path; see below
           for details.

           Added in version 251.

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

           Added in version 198.

       /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.

           Added in version 198.

       /etc/kernel/install.conf, /usr/lib/kernel/install.conf
           Configuration file with 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). The
           first of the files that is found will be used.  $KERNEL_INSTALL_CONF_ROOT may be used to
           override the search path; see below for details.

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

           Added in version 250.

       /etc/kernel/uki.conf
           Ini-style configuration file for ukify(1) which is only effective when
           $KERNEL_INSTALL_LAYOUT or layout= in install.conf is set to uki and
           $KERNEL_INSTALL_UKI_GENERATOR or uki_generator= in install.conf is set to ukify, or is
           unset.  $KERNEL_INSTALL_CONF_ROOT may be used to override the search path; see below for
           details.

           Added in version 255.

       /usr/lib/modules/KERNEL-VERSION/
           Location for installed kernel modules and other kernel related resources. For each
           locally installed kernel a directory named after the kernel version (uname -r) is kept.

           Added in version 255.

       /usr/lib/modules/KERNEL-VERSION/vmlinuz
           Location for installed kernel images. This is the recommended location for OS package
           managers to install kernel images into (as applicable), from which kernel-install add
           then copies it into the final boot partition.

           Added in version 255.

       For various cases listed above, if the $KERNEL_INSTALL_CONF_ROOT environment variable is set,
       it will override the search path. The files will be loaded only from the directory specified
       by the environment variable. When the variable is not set, the listed paths are tried in
       turn, and the first file that exists is used.

SEE ALSO
       machine-id(5), os-release(5), depmod(8), systemd-boot(7), ukify(1), 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

        3. Discoverable Partitions Specification
           https://uapi-group.org/specifications/specs/discoverable_partitions_specification

systemd 255                                                                        KERNEL-INSTALL(8)