systemd/man/kernel-install.xml

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<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">COMMAND</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>
  </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://systemd.io/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>.
            It also creates a boot loader entry according to the <ulink
            url="https://systemd.io/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>
          </itemizedlist>
        </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>$BOOT/loader/entries/<replaceable>ENTRY-TOKEN</replaceable>-<replaceable>KERNEL-VERSION</replaceable>.conf</filename>.</para></listitem>
          </itemizedlist>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><command>inspect</command></term>
        <listitem>
          <para>Shows the various paths and parameters configured or auto-detected. In particular shows the
          values of the various <varname>$KERNEL_INSTALL_*</varname> environment variables listed
          below.</para>
        </listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

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

    <para>The partition where the kernels and <ulink url="https://systemd.io/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>
      <varlistentry>
        <term><option>-v</option></term>
        <term><option>--verbose</option></term>
        <listitem>
          <para>Output additional information about operations being performed.</para>
        </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>$KERNEL_INSTALL_LAYOUT=bls|other|...</varname> is set for the plugins to specify the
      installation layout. Defaults to <option>bls</option> if
      <filename>$BOOT/<replaceable>ENTRY-TOKEN</replaceable></filename> exists, or <option>other</option>
      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 <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://systemd.io/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>other</term>
          <listitem>
            <para>Some other layout not understood natively by <command>kernel-install</command>.</para>
          </listitem>
        </varlistentry>
      </variablelist>

      <para><varname>$KERNEL_INSTALL_INITRD_GENERATOR</varname> is set for plugins to select the initrd
      generator. This may be configured as <varname>initrd_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.</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>
          </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>$KERNEL_INSTALL_CONF_ROOT</varname>
            may be used to override the path.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/kernel/tries</filename>
        </term>
          <listitem>
            <para>Read by <filename>90-loaderentry.install</filename>. If this file exists a numeric value is read from
            it and the naming of the generated entry file is slightly altered to include it as
            <filename>$BOOT/loader/entries/<replaceable>MACHINE-ID</replaceable>-<replaceable>KERNEL-VERSION</replaceable>+<replaceable>TRIES</replaceable>.conf</filename>. 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>$KERNEL_INSTALL_CONF_ROOT</varname> may be used to override the path.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/kernel/entry-token</filename>
        </term>
          <listitem>
            <para>If this file exists it is read and used as "entry token" for this system, i.e. is used for
            naming Boot Loader Specification entries, see <varname>$KERNEL_INSTALL_ENTRY_TOKEN</varname>
            above for details. <varname>$KERNEL_INSTALL_CONF_ROOT</varname> may be used to override the
            path.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/machine-id</filename>
        </term>
          <listitem>
            <para>The content of this file specifies the machine identification
            <replaceable>MACHINE-ID</replaceable>.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/etc/os-release</filename>
          <filename>/usr/lib/os-release</filename>
        </term>
        <listitem>
            <para>Read by <filename>90-loaderentry.install</filename>.
            If available, <varname>PRETTY_NAME=</varname> is read from these files and used as the title of the boot menu entry.
            Otherwise, <literal>Linux <replaceable>KERNEL-VERSION</replaceable></literal> will be used.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <filename>/usr/lib/kernel/install.conf</filename>
          <filename>/etc/kernel/install.conf</filename>
        </term>
          <listitem>
            <para>Configuration options for <command>kernel-install</command>, as a series of
            <varname>KEY=</varname><replaceable>VALUE</replaceable> assignments, compatible with shell
            syntax, following the same rules as described in
            <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
            <filename>/etc/kernel/install.conf</filename> will be read if present, and
            <filename>/usr/lib/kernel/install.conf</filename> otherwise. This file is optional.
            <varname>$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>.
            See the Environment variables section above for details.</para>
          </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>,
      <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>
    </para>
  </refsect1>

</refentry>