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...] 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.
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.
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|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.
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. If this file exists a numeric value
is read from it and the naming of the generated entry file is
slightly altered to include it as
$BOOT/loader/entries/MACHINE-ID-KERNEL-VERSION+TRIES.conf. 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://systemd.io/BOOT_LOADER_SPECIFICATION
systemd 252 KERNEL-INSTALL(8)
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