"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
+ SPDX-License-Identifier: LGPL-2.1+
+
This file is part of systemd.
Copyright 2014 Zbigniew Jędrzejewski-Szmek
<refnamediv>
<refname>systemd-coredump</refname>
- <refpurpose>Log and store core dumps</refpurpose>
+ <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>.</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>
- <para><command>systemd-coredump</command> can be used as a helper
- binary by the kernel when a user space program receives a fatal
- signal and dumps core. For it to be used in this capacity, it must
- be specified by the
- <varname>kernel.core_pattern</varname> <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
- setting. Systemd installs
- <filename>/usr/lib/sysctl.d/50-coredump.conf</filename> which
- configures <varname>kernel.core_pattern</varname> to invoke
- <command>systemd-coredump</command>. This file may be masked or
- overridden to use a different setting following normal
- <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> rules.</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 coredump will only be processed when the
- related resource limits are high enough. For programs started by
- <command>systemd</command>, those may be set using
- <varname>LimitCore=</varname> (see
- <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
+ <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><command>systemd-coredump</command> will log the coredump
- including a backtrace if possible, and store the core (contents of
- process' memory contents) in an external file on disk in
- <filename>/var/lib/systemd/coredump</filename>, or directly in
- the journal. This behavior may be modified using
- <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</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>Apart from the
+ <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>
- log viewer,
+ as usual.
<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- may be used to list and extract coredumps.</para>
+ 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>
<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>.
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