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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<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 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>. These core dumps are deleted after a few days by
default; see <filename>/usr/lib/tmpfiles.d/systemd.conf</filename> for details.</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 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>
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