systemd/man/loader.conf.xml

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<refentry id="loader.conf" conditional='HAVE_GNU_EFI'
    xmlns:xi="http://www.w3.org/2001/XInclude">
  <refentryinfo>
    <title>loader.conf</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>loader.conf</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>loader.conf</refname>
    <refpurpose>Configuration file for systemd-boot</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename><replaceable>ESP</replaceable>/loader/loader.conf</filename>,
    <filename><replaceable>ESP</replaceable>/loader/entries/*.conf</filename>
    <filename><replaceable>XBOOTLDR</replaceable>/loader/entries/*.conf</filename>
    </para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>
    <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> will
    read <filename><replaceable>ESP</replaceable>/loader/loader.conf</filename>, and any files with the
    <literal>.conf</literal> extension under
    <filename><replaceable>ESP</replaceable>/loader/entries/</filename> on the EFI system partition (ESP),
    and <filename><replaceable>XBOOTLDR</replaceable>/loader/entries/</filename> on the extended boot loader
    partition (XBOOTLDR) as defined by <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader
    Specification</ulink>.
    </para>

    <para>Each of these configuration files must consist of series of newline (i.e. ASCII code 10) separated
    lines, each consisting of an option name, followed by whitespace, and the option
    value. <literal>#</literal> may be used to start a comment line. Empty and comment lines are ignored. The
    files use UTF-8 encoding.</para>

    <para>Boolean arguments may be written as
    <literal>yes</literal>/<literal>y</literal>/<literal>true</literal>/<literal>t</literal>/<literal>on</literal>/<literal>1</literal> or
    <literal>no</literal>/<literal>n</literal>/<literal>false</literal>/<literal>f</literal>/<literal>off</literal>/<literal>0</literal>.
    </para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>The configuration options supported by
    <filename><replaceable>ESP</replaceable>/loader/entries/*.conf</filename> and
    <filename><replaceable>XBOOTLDR</replaceable>/loader/entries/*.conf</filename> files are defined as part
    of the <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader
    Specification</ulink>.</para>

    <para>The following configuration are supported by the <filename>loader.conf</filename> configuration
    file:</para>

    <variablelist>
      <varlistentry>
        <term>default</term>

        <listitem><para>A glob pattern to select the default entry. The default entry
        may be changed in the boot menu itself, in which case the name of the
        selected entry will be stored as an EFI variable, overriding this option.
        </para>

        <para>If set to <literal>@saved</literal> the chosen entry will be saved as an EFI variable
        on every boot and automatically selected the next time the boot loader starts.</para>

        <table>
          <title>Automatically detected entries will use the following names:</title>

          <tgroup cols='2'>
            <colspec colname='name' />
            <colspec colname='expl' />
            <thead>
              <row>
                <entry>Name</entry>
                <entry>Description</entry>
              </row>
            </thead>
            <tbody>
              <row>
                <entry>auto-efi-default</entry>
                <entry>EFI Default Loader</entry>
              </row>
              <row>
                <entry>auto-efi-shell</entry>
                <entry>EFI Shell</entry>
              </row>
              <row>
                <entry>auto-osx</entry>
                <entry>macOS</entry>
              </row>
              <row>
                <entry>auto-reboot-to-firmware-setup</entry>
                <entry>Reboot Into Firmware Interface</entry>
              </row>
              <row>
                <entry>auto-windows</entry>
                <entry>Windows Boot Manager</entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        <para>Supported glob wildcard patterns are <literal>?</literal>, <literal>*</literal>, and
        <literal>[…]</literal> (including ranges). Note that these patterns use the same syntax as
        <citerefentry project='man-pages'><refentrytitle>glob</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        but do not support all features. In particular, set negation and named character classes are not
        supported. The matching is done case-insensitively on the entry ID (as shown by <command>bootctl
        list</command>).</para></listitem>
      </varlistentry>

      <varlistentry>
        <term>timeout</term>

        <listitem><para>How long the boot menu should be shown before the default
        entry is booted, in seconds. This may be changed in the boot menu itself and
        will be stored as an EFI variable in that case, overriding this option.
        </para>

        <para>If set to <literal>menu-hidden</literal> or <literal>0</literal> (the default) no menu
        is shown and the default entry will be booted immediately. The menu can be shown
        by pressing and holding a key before systemd-boot is launched. Setting this to
        <literal>menu-force</literal> disables the timeout while always showing the menu.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>console-mode</term>

        <listitem><para>This option configures the resolution of the console. Takes a
        number or one of the special values listed below. The following values may be
        used:</para>

        <variablelist>
          <varlistentry>
            <term>0</term>
            <listitem>
              <para>Standard UEFI 80x25 mode</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>1</term>
            <listitem>
              <para>80x50 mode, not supported by all devices</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>2</term>
            <listitem>
              <para>the first non-standard mode provided by the device
              firmware, if any</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>auto</term>
            <listitem>
              <para>Pick a suitable mode automatically using heuristics</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>max</term>
            <listitem>
              <para>Pick the highest-numbered available mode</para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>keep</term>
            <listitem>
              <para>Keep the mode selected by firmware (the default)</para>
            </listitem>
          </varlistentry>
        </variablelist>

        </listitem>
      </varlistentry>

      <varlistentry>
        <term>editor</term>

        <listitem><para>Takes a boolean argument. Enable (the default) or disable the
        editor. The editor should be disabled if the machine can be accessed by
        unauthorized persons.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term>auto-entries</term>

        <listitem><para>Takes a boolean argument. Enable (the default) or disable
        entries for other boot entries found on the boot partition. In particular,
        this may be useful when loader entries are created to show replacement
        descriptions for those entries.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term>auto-firmware</term>

        <listitem><para>A boolean controlling the presence of the "Reboot into firmware" entry
        (enabled by default). If this is disabled, the firmware interface may still be reached
        by using the <keycap>f</keycap> key.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term>beep</term>

        <listitem><para>Takes a boolean argument. If timeout enabled beep every second, otherwise beep n times when n-th entry in boot menu is selected (default disabled).
        Currently, only x86 is supported, where it uses the PC speaker.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term>secure-boot-enroll</term>

        <listitem><para>Danger: this feature might soft-brick your device if used improperly.</para>

        <para>Takes one of <literal>off</literal>, <literal>manual</literal> or <literal>force</literal>.
        Controls the enrollment of secure boot keys. If set to <literal>off</literal>, no action whatsoever
        is taken. If set to <literal>manual</literal> (the default) and the UEFI firmware is in setup-mode
        then entries to manually enroll Secure Boot variables are created in the boot menu. If set to
        <literal>force</literal>, in addition, if a directory named <filename>/loader/keys/auto/</filename>
        exists on the ESP then the keys in that directory are enrolled automatically.</para>

        <para>The different sets of variables can be set up under <filename>/loader/keys/<replaceable>NAME</replaceable></filename>
        where <replaceable>NAME</replaceable> is the name that is going to be used as the name of the entry.
        This allows to ship multiple sets of Secure Boot variables and choose which one to enroll at runtime.</para>

        <para>Supported secure boot variables are one database for authorized images, one key exchange key (KEK)
        and one platform key (PK). For more information, refer to the <ulink url="https://uefi.org/specifications">UEFI specification</ulink>,
        under Secure Boot and Driver Signing. Another resource that describe the interplay of the different variables is the
        <ulink url="https://edk2-docs.gitbook.io/understanding-the-uefi-secure-boot-chain/secure_boot_chain_in_uefi/uefi_secure_boot">
        EDK2 documentation</ulink>.</para>

        <para>A complete set of UEFI variable includes <filename>db.esl</filename>, <filename>KEK.esl</filename>
        and <filename>PK.esl</filename>. Note that these files need to be authenticated UEFI variables. See
        below for an example of how to generate them from regular X.509 keys.</para>

        <programlisting>uuid=$(systemd-id128 new --uuid)
for key in PK KEK db; do
  openssl req -new -x509 -subj "/CN=${key}/" -keyout "${key}.key" -out "${key}.crt"
  openssl x509 -outform DER -in "${key}.crt" -out "${key}.cer"
  cert-to-efi-sig-list -g "${uuid}" "${key}.crt" "${key}.tmp"
done

sign-efi-sig-list -c PK.crt -k PK.key PK PK.tmp PK.esl
sign-efi-sig-list -c PK.crt -k PK.key KEK KEK.tmp KEK.esl
sign-efi-sig-list -c KEK.crt -k KEK.key db db.tmp db.esl
        </programlisting>

        <para>This feature is considered dangerous because even if all the required files are signed with the
        keys being loaded, some files necessary for the system to function properly still won't be. This
        is especially the case with Option ROMs (e.g. for storage controllers or graphics cards). See
        <ulink url="https://github.com/Foxboron/sbctl/wiki/FAQ#option-rom">Secure Boot and Option ROMs</ulink>
        for more details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term>reboot-for-bitlocker</term>

        <listitem><para>Caveat: This feature is experimental, and is likely to be changed (or removed in its
        current form) in a future version of systemd.</para>

        <para>Work around BitLocker requiring a recovery key when the boot loader was
        updated (disabled by default).</para>

        <para>Try to detect BitLocker encrypted drives along with an active TPM. If both are found
        and Windows Boot Manager is selected in the boot menu, set the <literal>BootNext</literal>
        EFI variable and restart the system. The firmware will then start Windows Boot Manager
        directly, leaving the TPM PCRs in expected states so that Windows can unseal the encryption
        key. This allows systemd-boot to be updated without having to provide the recovery key for
        BitLocker drive unlocking.</para>

        <para>Note that the PCRs that Windows uses can be configured with the
        <literal>Configure TPM platform validation profile for native UEFI firmware configurations</literal>
        group policy under <literal>Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption</literal>.
        When secure boot is enabled, changing this to PCRs <literal>0,2,7,11</literal> should be safe.
        The TPM key protector needs to be removed and then added back for the PCRs on an already
        encrypted drive to change. If PCR 4 is not measured, this setting can be disabled to speed
        up booting into Windows.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term>random-seed-mode</term>

        <listitem><para>Takes one of <literal>off</literal>, <literal>with-system-token</literal> and
        <literal>always</literal>. If <literal>off</literal> no random seed data is read off the ESP, nor
        passed to the OS. If <literal>with-system-token</literal> (the default)
        <command>systemd-boot</command> will read a random seed from the ESP (from the file
        <filename>/loader/random-seed</filename>) only if the <varname>LoaderSystemToken</varname> EFI
        variable is set, and then derive the random seed to pass to the OS from the combination. If
        <literal>always</literal> the boot loader will do so even if <varname>LoaderSystemToken</varname> is
        not set. This mode is useful in environments where protection against OS image reuse is not a
        concern, and the random seed shall be used even with no further setup in place. Use <command>bootctl
        random-seed</command> to initialize both the random seed file in the ESP and the system token EFI
        variable.</para>

        <para>See <ulink url="https://systemd.io/RANDOM_SEEDS">Random Seeds</ulink> for further
        information.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Example</title>

    <programlisting># /boot/efi/loader/loader.conf
timeout 0
default 01234567890abcdef1234567890abdf0-*
editor no
    </programlisting>

    <para>The menu will not be shown by default (the menu can still be shown by
    pressing and holding a key during boot). One of the entries with files with a
    name starting with <literal>01234567890abcdef1234567890abdf0-</literal> will be
    selected by default. If more than one entry matches, the one with the highest
    priority will be selected (generally the one with the highest version number).
    The editor will be disabled, so it is not possible to alter the kernel command
    line.</para>
  </refsect1>

  <refsect1>
      <title>See Also</title>
      <para>
        <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
      </para>
  </refsect1>
</refentry>