systemd/man/kernel-install.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="kernel-install" conditional='ENABLE_KERNEL_INSTALL'
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>kernel-install</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>kernel-install</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>kernel-install</refname>
    <refpurpose>Add and remove kernel and initrd images to and from /boot</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>kernel-install</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">add</arg>
      <arg choice="plain"><replaceable>KERNEL-VERSION</replaceable></arg>
      <arg choice="plain"><replaceable>KERNEL-IMAGE</replaceable></arg>
      <arg choice="opt" rep="repeat"><replaceable>INITRD-FILE</replaceable></arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>kernel-install</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">remove</arg>
      <arg choice="plain"><replaceable>KERNEL-VERSION</replaceable></arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>kernel-install</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain">inspect</arg>
      <arg choice="opt"><replaceable>KERNEL-IMAGE</replaceable></arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>
    <para><command>kernel-install</command> is used to install and remove kernel and initrd images
    <footnote>
      <para>Nowadays actually CPIO archives used as an "initramfs", rather than "initrd". See
      <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry> for an
      explanation.</para>
    </footnote>
    to and from the boot loader partition, referred to as <varname>$BOOT</varname> here. It will usually be
    one of <filename>/boot/</filename>, <filename>/efi/</filename>, or <filename>/boot/efi/</filename>, see
    below.</para>

    <para><command>kernel-install</command> will run the executable files ("plugins") located in the
    directory <filename>/usr/lib/kernel/install.d/</filename> and the local administration directory
    <filename>/etc/kernel/install.d/</filename>.  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 <filename>/etc/kernel/install.d/</filename> take precedence over files with the
    same name in <filename>/usr/lib/kernel/install.d/</filename>. This can be used to override a
    system-supplied executables with a local file if needed; a symbolic link in
    <filename>/etc/kernel/install.d/</filename> with the same name as an executable in
    <filename>/usr/lib/kernel/install.d/</filename>, pointing to <filename>/dev/null</filename>, disables the
    executable entirely. Executables must have the extension <literal>.install</literal>; other extensions
    are ignored.</para>

    <para>An executable placed in these directories should return <constant>0</constant> on success. It may
    also return <constant>77</constant> to cause the whole operation to terminate (executables later in
    lexical order will be skipped).</para>
  </refsect1>

  <refsect1>
    <title>Commands</title>
    <para>The following commands are understood:</para>
    <variablelist>
      <varlistentry>
        <term><command>add <replaceable>KERNEL-VERSION</replaceable> <replaceable>KERNEL-IMAGE</replaceable> [<replaceable>INITRD-FILE</replaceable> ...]</command></term>
        <listitem>
          <para>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). <command>kernel-install</command> calls the executable files from
          <filename>/usr/lib/kernel/install.d/*.install</filename> and
          <filename>/etc/kernel/install.d/*.install</filename> (i.e. the plugins) with the following
          arguments:</para>

          <programlisting>add <replaceable>KERNEL-VERSION</replaceable> <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename> <replaceable>KERNEL-IMAGE</replaceable> [<replaceable>INITRD-FILE</replaceable> ...]</programlisting>

          <para>The third argument directly refers to the path where to place kernel images, initrd
          images and other resources for <ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot
          Loader Specification</ulink> Type #1 entries (the "entry directory"). If other boot loader schemes
          are used the parameter may be ignored. The <replaceable>ENTRY-TOKEN</replaceable> string is
          typically the machine ID and is supposed to identify the local installation on the system. For
          details see below.</para>

          <para>Two default plugins execute the following operations in this case:</para>

          <itemizedlist>
            <listitem><para><command>kernel-install</command> creates
            <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable>/<replaceable>KERNEL-VERSION</replaceable></filename>,
            if enabled (see <varname>$KERNEL_INSTALL_LAYOUT</varname>).</para></listitem>

            <listitem><para><filename>50-depmod.install</filename> runs
            <citerefentry project='man-pages'><refentrytitle>depmod</refentrytitle><manvolnum>8</manvolnum></citerefentry> for the
            <replaceable>KERNEL-VERSION</replaceable>.</para></listitem>

            <listitem><para><filename>90-loaderentry.install</filename> copies
            <replaceable>KERNEL-IMAGE</replaceable> to
            <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/linux</filename>.
            If <replaceable>INITRD-FILE</replaceable>s are provided, it also copies them to
            <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable>/<replaceable>KERNEL_VERSION</replaceable>/<replaceable>INITRD-FILE</replaceable></filename>.
            This can also be used to prepend microcode before the actual initrd. It also creates a boot loader entry according to the <ulink
            url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink> (Type #1) in
            <filename>$BOOT/loader/entries/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>.conf</filename>.
            The title of the entry is the <replaceable>PRETTY_NAME</replaceable> parameter specified in
            <filename>/etc/os-release</filename> or <filename>/usr/lib/os-release</filename> (if the former
            is missing), or "Linux <replaceable>KERNEL-VERSION</replaceable>", if unset.</para>

            <para>If <varname>$KERNEL_INSTALL_LAYOUT</varname> is not "bls", this plugin does nothing.</para></listitem>

            <listitem><para><filename>90-uki-copy.install</filename> copies a file
            <filename>uki.efi</filename> from <varname>$KERNEL_INSTALL_STAGING_AREA</varname> or if it does
            not exist the <replaceable>KERNEL-IMAGE</replaceable> argument, only if it has a
            <literal>.efi</literal> extension, to
            <filename>$BOOT/EFI/Linux/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>.efi</filename>.</para>

            <para>If <varname>$KERNEL_INSTALL_LAYOUT</varname> is not "uki", this plugin does nothing.</para></listitem>
          </itemizedlist>

            <xi:include href="version-info.xml" xpointer="v241"/>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><command>remove <replaceable>KERNEL-VERSION</replaceable></command></term>
        <listitem>
          <para>This command expects a kernel version string as single argument. This calls executables from
          <filename>/usr/lib/kernel/install.d/*.install</filename> and
          <filename>/etc/kernel/install.d/*.install</filename> with the following arguments:
          </para>

          <programlisting>remove <replaceable>KERNEL-VERSION</replaceable> <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename></programlisting>

          <para>Afterwards, <command>kernel-install</command> removes the entry directory
          <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename>
          and its contents, if it exists.</para>

          <para>Two default plugins execute the following operations in this case:</para>

          <itemizedlist>
            <listitem><para><filename>50-depmod.install</filename> removes the files generated by <command>depmod</command> for this kernel again.</para></listitem>

            <listitem><para><filename>90-loaderentry.install</filename> removes the file
            <filename>$BOOT/loader/entries/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>.conf</filename>.</para></listitem>

            <listitem><para><filename>90-uki-copy.install</filename> removes the file
            <filename>$BOOT/EFI/Linux/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>.efi</filename>.</para></listitem>
          </itemizedlist>

            <xi:include href="version-info.xml" xpointer="v203"/>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><command>inspect [<replaceable>KERNEL-IMAGE</replaceable>]</command></term>
        <listitem>
          <para>Shows the various paths and parameters configured or auto-detected. In particular shows the
          values of the various <varname>$KERNEL_INSTALL_*</varname> environment variables listed
          below.</para>

          <xi:include href="version-info.xml" xpointer="v254"/>
        </listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>The <varname>$BOOT</varname> partition</title>

    <para>The partition where the kernels and <ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot
    Loader Specification</ulink> snippets are located is called <varname>$BOOT</varname>.
    <command>kernel-install</command> determines the location of this partition by checking
    <filename>/efi/</filename>, <filename>/boot/</filename>, and <filename>/boot/efi/</filename> in turn. The
    first location where <filename>$BOOT/loader/entries/</filename> or
    <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable>/</filename> exists is used.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>
    <para>The following options are understood:</para>

    <variablelist>
      <xi:include href="standard-options.xml" xpointer="esp-path"/>
      <xi:include href="standard-options.xml" xpointer="boot-path"/>

      <varlistentry>
        <term><option>--make-entry-directory=yes|no|auto</option></term>
        <listitem>
          <para>Controls creation and deletion of the
          <ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink>
          Type #1 entry directory on the file system containing resources such as kernel and initrd images
          during <option>add</option> and <option>remove</option>, respectively. The directory is named after
          the entry token, and is placed immediately below the boot root directory. When
          <literal>auto</literal>, the directory is created or removed only when the install layout is
          <literal>bls</literal>. Defaults to <literal>auto</literal>.</para>

          <xi:include href="version-info.xml" xpointer="v254"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--entry-token=</option></term>

        <listitem>
          <para>Controls how to name and identify boot loader entries for this kernel installation or
          deletion. Takes one of <literal>auto</literal>, <literal>machine-id</literal>,
          <literal>os-id</literal>, <literal>os-image-id</literal>, or an arbitrary string prefixed by
          <literal>literal:</literal> as argument.</para>

          <para>If set to <option>machine-id</option> the entries are named after the machine ID of the
          running system (e.g. <literal>b0e793a9baf14b5fa13ecbe84ff637ac</literal>). See
          <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
          details about the machine ID concept and file.</para>

          <para>If set to <option>os-id</option> the entries are named after the OS ID of the running system,
          i.e. the <varname>ID=</varname> field of
          <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          (e.g. <literal>fedora</literal>). Similarly, if set to <option>os-image-id</option> the entries are
          named after the OS image ID of the running system, i.e. the <varname>IMAGE_ID=</varname> field of
          <filename>os-release</filename> (e.g. <literal>vendorx-cashier-system</literal>).</para>

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

          <para>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) <varname>$BOOT_ROOT</varname>
          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.
          </para>

          <xi:include href="version-info.xml" xpointer="v254"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-v</option></term>
        <term><option>--verbose</option></term>
        <listitem>
          <para>Output additional information about operations being performed.</para>

        <xi:include href="version-info.xml" xpointer="v242"/>
        </listitem>
      </varlistentry>

      <xi:include href="standard-options.xml" xpointer="help" />
      <xi:include href="standard-options.xml" xpointer="version" />
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Environment variables</title>

    <refsect2>
      <title>Environment variables exported for plugins</title>

      <para>If <option>--verbose</option> is used, <varname>$KERNEL_INSTALL_VERBOSE=1</varname> will be
      exported for plugins. They may output additional logs in this case.</para>

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

      <para><varname>$KERNEL_INSTALL_ENTRY_TOKEN</varname> is set for the plugins to the desired entry
      "token" to use. It's an identifier that shall be used to identify the local installation, and is often
      the machine ID, i.e. same as <varname>$KERNEL_INSTALL_MACHINE_ID</varname>, but might also be a
      different type of identifier, for example a fixed string or the <varname>ID=</varname>,
      <varname>IMAGE_ID=</varname> values from <filename>/etc/os-release</filename>. 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.</para>

      <para>Note that while <varname>$KERNEL_INSTALL_ENTRY_TOKEN</varname> and
      <varname>$KERNEL_INSTALL_MACHINE_ID</varname> 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 <filename>/etc/kernel/entry-token</filename>, if it exists. Otherwise a
      few possible candidates below <varname>$BOOT</varname> are checked for Boot Loader Specification Type 1
      entry directories, and if found the entry token is derived from that. If that is not successful,
      <varname>$KERNEL_INSTALL_MACHINE_ID</varname> is used as fallback.</para>

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

      <para><varname>$KERNEL_INSTALL_LAYOUT=auto|bls|uki|other|...</varname> 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 <varname>layout=</varname> in
      <filename>install.conf</filename> upon initial installation. The following values are currently
      understood:</para>

      <variablelist>
        <varlistentry>
          <term>bls</term>
          <listitem>
            <para>Standard <ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader
            Specification</ulink> Type #1 layout, compatible with
            <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>:
            entries in
            <filename>$BOOT/loader/entries/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>[+<replaceable>TRIES</replaceable>].conf</filename>,
            kernel and initrds under
            <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename></para>
            <para>Implemented by <filename>90-loaderentry.install</filename>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term>uki</term>
          <listitem>
            <para>Standard <ulink
            url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader
            Specification</ulink> Type #2 layout, compatible with
            <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>:
            unified kernel images under <filename>$BOOT/EFI/Linux</filename> as
            <filename>$BOOT/EFI/Linux/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>[+<replaceable>TRIES</replaceable>].efi</filename>.</para>
            <para>Implemented by <filename>90-uki-copy.install</filename>.</para>

            <xi:include href="version-info.xml" xpointer="v253"/>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term>other</term>
          <listitem>
            <para>Some other layout not understood natively by <command>kernel-install</command>.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term>auto</term>
          <listitem>
            <para>Pick the layout automatically. If the kernel is a UKI set layout to
            <option>uki</option>. If not default to <option>bls</option> if
            <filename>$BOOT/loader/entries.srel</filename> with content <literal>type1</literal> or
            <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable></filename> exists, or
            <option>other</option> otherwise.</para>
            <para>Leaving layout blank has the same effect. This is the default.</para>

            <xi:include href="version-info.xml" xpointer="v254"/>
          </listitem>
        </varlistentry>
      </variablelist>

      <para><varname>$KERNEL_INSTALL_INITRD_GENERATOR</varname> and <varname>$KERNEL_INSTALL_UKI_GENERATOR</varname>
      are set for plugins to select the initrd and/or UKI generator. This may be configured as
      <varname>initrd_generator=</varname> and <varname>uki_generator=</varname> in <filename>install.conf</filename>, see below.</para>

      <para><varname>$KERNEL_INSTALL_STAGING_AREA</varname> 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 <filename>initrd*</filename> will be installed as <replaceable>INITRD-FILE</replaceable>s, 
      and files named <filename>microcode*</filename> will be prepended before <replaceable>INITRD-FILE</replaceable>s.</para>
      
    </refsect2>

    <refsect2>
      <title>Environment variables understood by <command>kernel-install</command></title>

      <para><varname>$KERNEL_INSTALL_CONF_ROOT</varname> can be set to override the location of the
      configuration files read by <command>kernel-install</command>. When set,
      <filename>install.conf</filename>, <filename>entry-token</filename>, and other files will be
      read from this directory.</para>

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

      <para><varname>$MACHINE_ID</varname> can be set for <command>kernel-install</command> to override
      <varname>$KERNEL_INSTALL_MACHINE_ID</varname>, the machine ID.</para>

      <para><varname>$BOOT_ROOT</varname> can be set for <command>kernel-install</command> to override
      <varname>$KERNEL_INSTALL_BOOT_ROOT</varname>, the installation location for boot entries.</para>

      <para>The last two variables may also be set in <filename>install.conf</filename>. Variables set in the
      environment take precedence over the values specified in the config file.</para>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Exit status</title>
    <para>If every executable returns 0 or 77, 0 is returned, and a non-zero failure code otherwise.</para>
  </refsect1>

  <refsect1>
    <title>Files</title>
    <variablelist>
      <varlistentry>
        <term>
          <filename>/usr/lib/kernel/install.d/*.install</filename>
          <filename>/etc/kernel/install.d/*.install</filename>
        </term>
          <listitem>
            <para>Drop-in files which are executed by kernel-install.</para>

          <xi:include href="version-info.xml" xpointer="v198"/>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/usr/lib/kernel/cmdline</filename>
          <filename>/etc/kernel/cmdline</filename>
          <filename>/proc/cmdline</filename>
        </term>
          <listitem>
            <para>Read by <filename>90-loaderentry.install</filename>. The content of the file
            <filename>/etc/kernel/cmdline</filename> specifies the kernel command line to use. If that file
            does not exist, <filename>/usr/lib/kernel/cmdline</filename> is used. If that also does not
            exist, <filename>/proc/cmdline</filename> is used. <varname>$KERNEL_INSTALL_CONF_ROOT</varname>
            may be used to override the path.</para>

          <xi:include href="version-info.xml" xpointer="v250"/>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/kernel/tries</filename>
        </term>
          <listitem>
            <para>Read by <filename>90-loaderentry.install</filename> and
            <filename>90-uki-copy.install</filename>. 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
            <filename>$BOOT/loader/entries/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>+<replaceable>TRIES</replaceable>.conf</filename>
            or
            <filename>$BOOT/EFI/Linux/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>+<replaceable>TRIES</replaceable>.efi</filename>, respectively. This
            is useful for boot loaders such as
            <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>
            which implement boot attempt counting with a counter embedded in the entry file name.
            <varname>$KERNEL_INSTALL_CONF_ROOT</varname> may be used to override the path.</para>

          <xi:include href="version-info.xml" xpointer="v240"/>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/kernel/entry-token</filename>
        </term>
          <listitem>
            <para>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 <varname>$KERNEL_INSTALL_ENTRY_TOKEN</varname>
            above for details. <varname>$KERNEL_INSTALL_CONF_ROOT</varname> may be used to override the
            path.</para>

            <xi:include href="version-info.xml" xpointer="v251"/>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/machine-id</filename>
        </term>
          <listitem>
            <para>The content of this file specifies the machine identification
            <replaceable>MACHINE-ID</replaceable>.</para>

            <xi:include href="version-info.xml" xpointer="v198"/>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/os-release</filename>
          <filename>/usr/lib/os-release</filename>
        </term>
        <listitem>
            <para>Read by <filename>90-loaderentry.install</filename>.
            If available, <varname>PRETTY_NAME=</varname> is read from these files and used as the title of the boot menu entry.
            Otherwise, <literal>Linux <replaceable>KERNEL-VERSION</replaceable></literal> will be used.</para>

        <xi:include href="version-info.xml" xpointer="v215"/>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/usr/lib/kernel/install.conf</filename>
          <filename>/etc/kernel/install.conf</filename>
        </term>
          <listitem>
            <para>Configuration options for <command>kernel-install</command>, as a series of
            <varname>KEY=</varname><replaceable>VALUE</replaceable> assignments, compatible with shell
            syntax, following the same rules as described in
            <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            <filename>/etc/kernel/install.conf</filename> will be read if present, and
            <filename>/usr/lib/kernel/install.conf</filename> otherwise. This file is optional.
            <varname>$KERNEL_INSTALL_CONF_ROOT</varname> may be used to override the path.
            </para>

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

            <xi:include href="version-info.xml" xpointer="v250"/>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/kernel/uki.conf</filename>
        </term>
          <listitem>
            <para>Ini-style configuration file for <citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry> which is only effective when <varname>$KERNEL_INSTALL_LAYOUT</varname> or <varname>layout=</varname> in <filename>install.conf</filename> is set to <option>uki</option> and <varname>$KERNEL_INSTALL_UKI_GENERATOR</varname> or <varname>uki_generator=</varname> in <filename>install.conf</filename> is set to <option>ukify</option>.
            <varname>$KERNEL_INSTALL_CONF_ROOT</varname> may be used to override the path.
            </para>

          <xi:include href="version-info.xml" xpointer="v255"/>
          </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>depmod</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>ukify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink>
    </para>
  </refsect1>

</refentry>