niceSOFT/systemd: The systemd System and Service Manager

man/systemd-debug-generator.xml
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Luca Boccassi
Fix typos found by Lintian
24 июл 2025, 12:38
24 июл 2025, 12:3828eec22
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="systemd-debug-generator" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-debug-generator</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-debug-generator</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-debug-generator</refname>
    <refpurpose>Generator for enabling a runtime debug shell and
    masking specific units at boot</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>/usr/lib/systemd/system-generators/systemd-debug-generator</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>systemd-debug-generator</command> is a generator that provides some debugging
    functionality.</para>

    <para><command>systemd-debug-generator</command> implements
    <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
  </refsect1>

  <refsect1>
    <title>Kernel Command Line</title>

    <para><command>systemd-debug-generator</command> understands the following kernel command line
    parameters:</para>

    <variablelist class='kernel-commandline-options'>

      <varlistentry>
        <term><varname>systemd.mask=</varname></term>
        <term><varname>rd.systemd.mask=</varname></term>

        <listitem><para>These options take a unit name as argument. The unit specified is masked for the
        runtime (i.e. for this session — from boot to shutdown), similarly to the effect of
        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
        <command>mask</command> command. This is useful to boot with certain units removed from the initial
        boot transaction for debugging system startup. May be specified more than once. The option prefixed
        with <literal>rd.</literal> is honored only in the initrd, while the one without prefix is only
        honored on the host.</para>

        <xi:include href="version-info.xml" xpointer="v215"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>systemd.wants=</varname></term>
        <term><varname>rd.systemd.wants=</varname></term>

        <listitem><para>These options take a unit name as argument. A start job for this unit is added to the
        initial transaction. This is useful to start one or more additional units at boot. May be specified
        more than once. The option prefixed with <literal>rd.</literal> is honored only in the initrd, while
        the one that is not prefixed only on the host.</para>

        <xi:include href="version-info.xml" xpointer="v215"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>systemd.debug_shell</varname></term>
        <term><varname>rd.systemd.debug_shell</varname></term>
        <term><varname>systemd.default_debug_tty=</varname></term>
        <term><varname>rd.systemd.default_debug_tty=</varname></term>

        <listitem><para>If the <option>systemd.debug_shell</option> or
        <option>rd.systemd.debug_shell</option> option is specified, the debug shell service
        <literal>debug-shell.service</literal> is pulled into the boot transaction and a debug shell will be
        spawned during early boot. By default, <filename>&DEBUGTTY;</filename> is used, but a specific tty
        can also be specified, either with or without the <filename>/dev/</filename> prefix. To set the tty
        to use without enabling the debug shell, the <option>systemd.default_debug_tty=</option> option can
        be used which also takes a tty with or without the <filename>/dev/</filename> prefix. Note that the
        shell may also be turned on persistently by enabling it with
        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
        <command>enable</command> command. The options prefixed with <literal>rd.</literal> are honored only
        in the initrd, while the ones without prefix are only honored on the host.</para>

        <xi:include href="version-info.xml" xpointer="v215"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>systemd.break=</varname></term>
        <term><varname>rd.systemd.break=</varname></term>

        <listitem><para>Takes one of <option>pre-udev</option>, <option>pre-basic</option>,
        <option>pre-mount</option>, or <option>pre-switch-root</option> (the default for the
        <literal>rd.</literal> option). It also accepts multiple values separated by comma
        (<literal>,</literal>). These options allow one to pause the boot process at a certain point and spawn
        a debug shell. After exiting this shell, the system will resume booting. The option prefixed with
        <literal>rd.</literal> is honored only in the initrd, while the one without prefix is only honored on
        the host.</para>

        <table>
          <title>Available breakpoints</title>

          <tgroup cols='4'>
            <colspec colname='breakpoint' />
            <colspec colname='description' />
            <colspec colname='initrd' />
            <colspec colname='host' />
            <thead>
              <row>
                <entry>Breakpoints</entry>
                <entry>Description</entry>
                <entry>Can be used in the initrd</entry>
                <entry>Can be used on the host</entry>
              </row>
            </thead>
            <tbody>
              <row>
                <entry><option>pre-udev</option></entry>
                <entry>Before starting to process kernel uevents, i.e., before <filename>systemd-udevd.service</filename> starts.</entry>
                <entry>✓</entry>
                <entry>✓</entry>
              </row>
              <row>
                <entry><option>pre-basic</option></entry>
                <entry>Before leaving early boot and regular services start, i.e., before <filename>basic.target</filename> is reached.</entry>
                <entry>✓</entry>
                <entry>✓</entry>
              </row>
              <row>
                <entry><option>pre-mount</option></entry>
                <entry>Before the root filesystem is mounted, i.e., before <filename>sysroot.mount</filename> starts.</entry>
                <entry>✓</entry>
                <entry>✗</entry>
              </row>
              <row>
                <entry><option>pre-switch-root</option></entry>
                <entry>Before switching from the initrd to the real root.</entry>
                <entry>✓</entry>
                <entry>✗</entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        <xi:include href="version-info.xml" xpointer="v258"/></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>System Credentials</title>

    <variablelist class='system-credentials'>
      <varlistentry>
        <term><varname>systemd.extra-unit.*</varname></term>

        <listitem><para>Credentials prefixed with <literal>systemd.extra-unit.</literal> specify additional
        units to add to the final system. Note that these additional units are added to both the initrd and
        the final system. <varname>ConditionPathExists=!/etc/initrd-release</varname> can be used to make
        sure the unit is conditioned out in the initrd. Note that this can also be used to mask units, by
        simply specifying an empty value.</para>

        <xi:include href="version-info.xml" xpointer="v256"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>systemd.unit-dropin.*</varname></term>

        <listitem><para>Credentials prefixed with <literal>systemd.unit-dropin.</literal> add drop-ins for
        the corresponding units in the final system. Each credential must be suffixed with the full unit name
        including the unit extension. Its contents must be a valid unit drop-in file. Optionally, the unit
        name may be followed with <literal>~</literal>, followed by the drop-in name without the
        <literal>.conf</literal> suffix. If not specified, the name of the generated drop-in will be
        <literal>50-credential.conf</literal>. Note that these additional drop-ins are added to both the
        initrd and the final system.</para>

        <xi:include href="version-info.xml" xpointer="v256"/></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd.system-credentials</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>