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debug-generator: add a kernel cmdline option to pause the boot process

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Introduce the `systemd.break=` kernel command line option to allow stopping the
boot process at a certain point and spawn a debug shell. After exiting this
shell, the system will resume booting.

It accepts the following values:
- `pre-udev`: before starting to process kernel uevents (initrd and host).
- `pre-basic`: before leaving early boot and regular services start (initrd and
host).
- `pre-mount`: before the root filesystem is mounted (initrd).
- `pre-switch-root`: before switching root (initrd).
This commit is contained in:
Antonio Alvarez Feijoo
2024-12-20 08:51:23 +01:00
parent cb3801a4c9
commit e9f781a5a4
9 changed files with 411 additions and 0 deletions
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man/systemd-debug-generator.xml
+61
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@@ -93,6 +93,66 @@
<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 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 in
the main system.</para>
<table>
<title>Available breakpoints</title>
<tgroup cols='4'>
<colspec colname='breakpoint' />
<colspec colname='description' />
<colspec colname='initrd' />
<colspec colname='main' />
<thead>
<row>
<entry>Breakpoints</entry>
<entry>Description</entry>
<entry>Can be used in the initrd</entry>
<entry>Can be used in the main system</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>
@@ -135,6 +195,7 @@
<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>