man/systemd-coredump.xml

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   6   SPDX-License-Identifier: LGPL-2.1+
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   8
   9 <refentry id="systemd-coredump" conditional='ENABLE_COREDUMP'
  10           xmlns:xi="http://www.w3.org/2001/XInclude">
  11
  12   <refentryinfo>
  13     <title>systemd-coredump</title>
  14     <productname>systemd</productname>
  15
  16     <authorgroup>
  17       <author>
  18         <contrib>Developer</contrib>
  19         <firstname>Lennart</firstname>
  20         <surname>Poettering</surname>
  21         <email>lennart@poettering.net</email>
  22       </author>
  23     </authorgroup>
  24   </refentryinfo>
  25
  26   <refmeta>
  27     <refentrytitle>systemd-coredump</refentrytitle>
  28     <manvolnum>8</manvolnum>
  29   </refmeta>
  30
  31   <refnamediv>
  32     <refname>systemd-coredump</refname>
  33     <refname>systemd-coredump.socket</refname>
  34     <refname>systemd-coredump@.service</refname>
  35     <refpurpose>Acquire, save and process core dumps</refpurpose>
  36   </refnamediv>
  37
  38   <refsynopsisdiv>
  39     <para><filename>/usr/lib/systemd/systemd-coredump</filename></para>
  40     <para><filename>/usr/lib/systemd/systemd-coredump</filename> <option>--backtrace</option></para>
  41     <para><filename>systemd-coredump@.service</filename></para>
  42     <para><filename>systemd-coredump.socket</filename></para>
  43   </refsynopsisdiv>
  44
  45   <refsect1>
  46     <title>Description</title>
  47     <para><filename>systemd-coredump@.service</filename> is a system service that can acquire core
  48     dumps from the kernel and handle them in various ways. The <command>systemd-coredump</command>
  49     executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
  50     second time in the <filename>systemd-coredump@.service</filename> to actually write the data to
  51     the journal.</para>
  52
  53     <para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs
  54     in privileged mode, and will connect to the socket created by the
  55     <filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
  56     <filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
  57     <filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename>
  58     are helper units which do the actual processing of core dumps and are subject to normal service
  59     management.</para>
  60
  61     <para>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
  62     for further processing, for example in
  63     <citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
  64     </para>
  65
  66     <para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
  67     if possible to the journal and store the core dump itself in an external file in
  68     <filename>/var/lib/systemd/coredump</filename>.</para>
  69
  70     <para>The behavior of a specific program upon reception of a signal is governed by a few
  71     factors which are described in detail in
  72     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  73     In particular, the core dump will only be processed when the related resource limits are sufficient.
  74     </para>
  75
  76     <para>It is also possible to invoke <command>systemd-coredump</command> with
  77     <option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects
  78     a journal entry in the journal
  79     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
  80     on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
  81     metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append
  82     additional metadata fields in the same way it does for core dumps received from the kernel. In
  83     this mode, no core dump is stored in the journal.</para>
  84   </refsect1>
  85
  86   <refsect1>
  87     <title>Configuration</title>
  88     <para>For programs started by <command>systemd</command> process resource limits can be set by directive
  89     <varname>LimitCore=</varname>, see
  90     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  91     </para>
  92
  93     <para>In order to be used by the kernel to handle core dumps,
  94     <command>systemd-coredump</command> must be configured in
  95     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  96     parameter <varname>kernel.core_pattern</varname>. The syntax of this parameter is explained in
  97     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  98     systemd installs the file <filename>/usr/lib/sysctl.d/50-coredump.conf</filename> which configures
  99     <varname>kernel.core_pattern</varname> accordingly. This file may be masked or overridden to use a different
 100     setting following normal
 101     <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 102     rules. If the sysctl configuration is modified, it must be updated in the kernel before it
 103     takes effect, see
 104     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 105     and
 106     <citerefentry><refentrytitle>systemd-sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 107     </para>
 108
 109     <para>In order to by used in the <option>--backtrace</option> mode, an appropriate backtrace
 110     handler must be installed on the sender side. For example, in case of
 111     <citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry>, this
 112     means a <varname>sys.excepthook</varname> must installed, see
 113     <ulink url="https://github.com/keszybz/systemd-coredump-python">systemd-coredump-python</ulink>.
 114     </para>
 115
 116     <para>The behavior of <command>systemd-coredump</command> itself is configured through the configuration file
 117     <filename>/etc/systemd/coredump.conf</filename> and corresponding snippets
 118     <filename>/etc/systemd/coredump.conf.d/*.conf</filename>, see
 119     <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. A new
 120     instance of <command>systemd-coredump</command> is invoked upon receiving every core dump. Therefore, changes
 121     in these files will take effect the next time a core dump is received.</para>
 122
 123     <para>Resources used by core dump files are restricted in two ways. Parameters like maximum size of acquired
 124     core dumps and files can be set in files <filename>/etc/systemd/coredump.conf</filename> and snippets mentioned
 125     above. In addition the storage time of core dump files is restricted by <command>systemd-tmpfiles</command>,
 126     corresponding settings are by default in <filename>/usr/lib/tmpfiles.d/systemd.conf</filename>.</para>
 127
 128     <refsect2>
 129       <title>Disabling coredump processing</title>
 130
 131       <para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>,
 132       set <programlisting>Storage=none
 133 ProcessSizeMax=0</programlisting> in
 134       <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 135       </para>
 136     </refsect2>
 137   </refsect1>
 138
 139   <refsect1>
 140     <title>Usage</title>
 141     <para>Data stored in the journal can be viewed with
 142     <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 143     as usual.
 144     <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 145     can be used to retrieve saved core dumps independent of their location, to display information and to process
 146     them e.g. by passing to the GNU debugger (gdb).</para>
 147   </refsect1>
 148
 149   <refsect1>
 150     <title>See Also</title>
 151     <para>
 152       <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 153       <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 154       <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 155       <citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 156       <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 157       <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 158       <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 159     </para>
 160   </refsect1>
 161 </refentry>