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)
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