systemd/man/loader.conf.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">
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<refentry id="loader.conf" conditional='ENABLE_BOOTLOADER'
    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://uapi-group.org/specifications/specs/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://uapi-group.org/specifications/specs/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>Controls enrollment of secure boot keys found on the ESP if the system is in setup mode:
        <variablelist>
          <varlistentry>
            <term><option>off</option></term>
            <listitem><para>No action is taken.</para></listitem>
          </varlistentry>

          <varlistentry>
            <term><option>manual</option></term>
            <listitem><para>Boot entries for found secure boot keys are created that allow manual
            enrollment.</para></listitem>
          </varlistentry>

          <varlistentry>
            <term><option>if-safe</option></term>
            <listitem><para>Same behavior as <option>manual</option>, but will try to automatically
            enroll the key <literal>auto</literal> if it is considered to be safe. Currently, this is only
            the case if the system is running inside a virtual machine.</para></listitem>
          </varlistentry>

          <varlistentry>
            <term><option>force</option></term>
            <listitem><para>Always enroll the <literal>auto</literal> key if found. Note that a warning
            message with a timeout will still be shown if this operation is unknown to be safe.</para></listitem>
          </varlistentry>
        </variablelist>
        </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 one 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.auth</filename>, <filename>KEK.auth</filename>
        and <filename>PK.auth</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}.der"
  sbsiglist --owner "${uuid}" --type x509 --output "${key}.esl" "${key}.der"
done

for key in MicWinProPCA2011_2011-10-19.crt MicCorUEFCA2011_2011-06-27.crt MicCorKEKCA2011_2011-06-24.crt; do
  curl "https://www.microsoft.com/pkiops/certs/${key}" --output "${key}"
  sbsiglist --owner 77fa9abd-0359-4d32-bd60-28f4e78f784b --type x509 --output "${key%crt}esl" "${key}"
done

# Optionally add Microsoft Windows Production CA 2011 (needed to boot into Windows).
cat MicWinProPCA2011_2011-10-19.esl >>db.esl

# Optionally add Microsoft Corporation UEFI CA 2011 for firmware drivers / option ROMs
# and third-party boot loaders (including shim). This is highly recommended on real
# hardware as not including this may soft-brick your device (see next paragraph).
cat MicCorUEFCA2011_2011-06-27.esl >>db.esl

# Optionally add Microsoft Corporation KEK CA 2011. Recommended if either of the
# Microsoft keys is used as the official UEFI revocation database is signed with this
# key. The revocation database can be updated with <citerefentry project='man-pages'><refentrytitle>fwupdmgr</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
cat MicCorKEKCA2011_2011-06-24.esl >>KEK.esl

attr=NON_VOLATILE,RUNTIME_ACCESS,BOOTSERVICE_ACCESS,TIME_BASED_AUTHENTICATED_WRITE_ACCESS
sbvarsign --attr ${attr} --key PK.key --cert PK.crt --output PK.auth PK PK.esl
sbvarsign --attr ${attr} --key PK.key --cert PK.crt --output KEK.auth KEK KEK.esl
sbvarsign --attr ${attr} --key KEK.key --cert KEK.crt --output db.auth db 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
        <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> 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>
    </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>