systemd/man/systemd-coredump.xml

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<refentry id="systemd-coredump" conditional='ENABLE_COREDUMP'
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-coredump</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-coredump</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-coredump</refname>
    <refname>systemd-coredump.socket</refname>
    <refname>systemd-coredump@.service</refname>
    <refpurpose>Acquire, save and process core dumps</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>/usr/lib/systemd/systemd-coredump</filename></para>
    <para><filename>/usr/lib/systemd/systemd-coredump</filename> <option>--backtrace</option></para>
    <para><filename>systemd-coredump@.service</filename></para>
    <para><filename>systemd-coredump.socket</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>
    <para><filename>systemd-coredump@.service</filename> is a system service to process core dumps. It will
    log a summary of the event to
    <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
    including information about the process identifier, owner, the signal that killed the process, and the
    stack trace if possible. It may also save the core dump for later processing.</para>

    <para>The behavior of a specific program upon reception of a signal is governed by a few
    factors which are described in detail in
    <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    In particular, the core dump will only be processed when the related resource limits are sufficient.
    </para>

    <para>Core dumps can be written to the journal or saved as a file. In both cases, they can be retrieved
    for further processing, for example in
    <citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
    See <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
    in particular the <command>list</command> and <command>debug</command> verbs.</para>

    <para>By default, <command>systemd-coredump</command> will log the core dump to the journal, including a
    backtrace if possible, and store the core dump (an image of the memory contents of the process) itself in
    an external file in <filename>/var/lib/systemd/coredump</filename>. These core dumps are deleted after a
    few days by default; see <filename>/usr/lib/tmpfiles.d/systemd.conf</filename> for details. Note that the
    removal of core files from the file system and the purging of journal entries are independent, and the
    core file may be present without the journal entry, and journal entries may point to since-removed core
    files. Metadata is attached to core files in the form of extended attributes, so the core files may be
    useful even without the full metadata available in the journal entry.
    </para>

    <refsect2>
      <title>Invocation of <command>systemd-coredump</command></title>

      <para>The <command>systemd-coredump</command> executable does the actual work. It is invoked twice:
      once as the handler by the kernel, and the second time in the
      <filename>systemd-coredump@.service</filename> to actually write the data to the journal and process
      and save the core file.</para>

      <para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs in
      privileged mode, and will connect to the socket created by the
      <filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
      <filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
      <filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename> are
      helper units which do the actual processing of core dumps and are subject to normal service
      management.</para>

      <para>It is also possible to invoke <command>systemd-coredump</command> with
      <option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects a
      journal entry in the journal
      <ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
      on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
      metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append additional
      metadata fields in the same way it does for core dumps received from the kernel. In this mode, no core
      dump is stored in the journal.</para>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Configuration</title>
    <para>For programs started by <command>systemd</command>, process resource limits can be set by directive
    <varname>LimitCORE=</varname>, see
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    </para>

    <para>In order to be used by the kernel to handle core dumps,
    <command>systemd-coredump</command> must be configured in
    <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    parameter <varname>kernel.core_pattern</varname>. The syntax of this parameter is explained in
    <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    systemd installs the file <filename>/usr/lib/sysctl.d/50-coredump.conf</filename> which configures
    <varname>kernel.core_pattern</varname> accordingly. This file may be masked or overridden to use a different
    setting following normal
    <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    rules. If the sysctl configuration is modified, it must be updated in the kernel before it
    takes effect, see
    <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    and
    <citerefentry><refentrytitle>systemd-sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    </para>

    <para>In order to be used in the <option>--backtrace</option> mode, an appropriate backtrace
    handler must be installed on the sender side. For example, in case of
    <citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry>, this
    means a <varname>sys.excepthook</varname> must be installed, see
    <ulink url="https://github.com/keszybz/systemd-coredump-python">systemd-coredump-python</ulink>.
    </para>

    <para>The behavior of <command>systemd-coredump</command> itself is configured through the configuration file
    <filename>/etc/systemd/coredump.conf</filename> and corresponding snippets
    <filename>/etc/systemd/coredump.conf.d/*.conf</filename>, see
    <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. A new
    instance of <command>systemd-coredump</command> is invoked upon receiving every core dump. Therefore, changes
    in these files will take effect the next time a core dump is received.</para>

    <para>Resources used by core dump files are restricted in two ways. Parameters like maximum size of acquired
    core dumps and files can be set in files <filename>/etc/systemd/coredump.conf</filename> and snippets mentioned
    above. In addition the storage time of core dump files is restricted by <command>systemd-tmpfiles</command>,
    corresponding settings are by default in <filename>/usr/lib/tmpfiles.d/systemd.conf</filename>. The default is
    to delete core dumps after a few days; see the above file for details.</para>

    <refsect2>
      <title>Disabling coredump processing</title>

      <para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>, set
      <programlisting>Storage=none ProcessSizeMax=0</programlisting> in
      <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
      </para>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Usage</title>
    <para>Data stored in the journal can be viewed with
    <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> as usual.
    <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> can be
    used to retrieve saved core dumps independent of their location, to display information and to process
    them e.g. by passing to the GNU debugger (gdb).</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    </para>
  </refsect1>
</refentry>