kernel-install(8)

NAME#

kernel-install - Add and remove kernel and initrd images to and from the boot partition

SYNOPSIS#

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

kernel-install [OPTIONS...] add-all

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 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...]]

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 \nKERNEL-VERSION\n $BOOT/\nENTRY-TOKEN\n/\nKERNEL-VERSION\n/ \nKERNEL-IMAGE\n \
\n
          [\nINITRD-FILE\n ...]

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:

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

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

Added in version 198.

add-all

Added in version 255.

removeKERNEL-VERSION

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 \nKERNEL-VERSION\n $BOOT/\nENTRY-TOKEN\n/\nKERNEL-VERSION\n/

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:

Added in version 198.

inspect [[[KERNEL-VERSION]KERNEL-IMAGE] [INITRD-FILE...]]

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

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=

--boot-path=

--make-entry-directory=yes|no|auto

Added in version 254.

--entry-token=

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

Added in version 242.

--root=root

Added in version 255.

--image=image

Added in version 255.

-h, --help

--version

--no-pager

--json=MODE

--image-policy=policy

--no-legend

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

Added in version 254.

pe

Added in version 254.

unknown

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 is 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 is encouraged to declare its own layout name and configure layout= in install.conf upon initial installation. The following values are currently understood:

bls

Implemented by 90-loaderentry.install.

Added in version 250.

uki

Implemented by 90-uki-copy.install.

Added in version 253.

other

Added in version 250.

auto

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 only. Note that this path is relative to the host, and in particular symlinks in this directory are resolved relative to the host, even if --root=root is used. This means that it is generally not correct to use this variable to specify a directory underneath root if symlinks are used there.

$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

Added in version 198.

/etc/kernel/cmdline, /usr/lib/kernel/cmdline, /proc/cmdline

Added in version 198.

/etc/kernel/devicetree, /usr/lib/kernel/devicetree

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

Added in version 240.

/etc/kernel/entry-token

Added in version 251.

/etc/machine-id

Added in version 198.

/etc/os-release, /usr/lib/os-release

Added in version 198.

/etc/kernel/install.conf, /run/kernel/install.conf, /usr/local/lib/kernel/install.conf, /usr/lib/kernel/install.conf, /etc/kernel/install.conf.d/*.conf, /run/kernel/install.conf.d/*.conf, /usr/local/lib/kernel/install.conf.d/*.conf, /usr/lib/kernel/install.conf.d/*.conf

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

Added in version 255.

/usr/lib/modules/KERNEL-VERSION/

Added in version 255.

/usr/lib/modules/KERNEL-VERSION/vmlinuz

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

3.

Discoverable Partitions Specification