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>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </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>/lib/systemd/systemd-coredump</filename></para>
    <para><filename>/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 that can acquire core
    dumps from the kernel and handle them in various ways. 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.</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>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
    for further processing, for example in
    <citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
    </para>

    <para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
    if possible to the journal and store the core dump itself in an external file in
    <filename>/var/lib/systemd/coredump</filename>.</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>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>
  </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 by 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 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>.</para>
  </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>