man/systemd-coredump.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd-coredump" conditional='ENABLE_COREDUMP'
   7           xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>systemd-coredump</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd-coredump</refentrytitle>
  16     <manvolnum>8</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd-coredump</refname>
  21     <refname>systemd-coredump.socket</refname>
  22     <refname>systemd-coredump@.service</refname>
  23     <refpurpose>Acquire, save and process core dumps</refpurpose>
  24   </refnamediv>
  25
  26   <refsynopsisdiv>
  27     <para><filename>/usr/lib/systemd/systemd-coredump</filename></para>
  28     <para><filename>/usr/lib/systemd/systemd-coredump</filename> <option>--backtrace</option></para>
  29     <para><filename>systemd-coredump@.service</filename></para>
  30     <para><filename>systemd-coredump.socket</filename></para>
  31   </refsynopsisdiv>
  32
  33   <refsect1>
  34     <title>Description</title>
  35     <para><filename>systemd-coredump@.service</filename> is a system service that can acquire core
  36     dumps from the kernel and handle them in various ways. The <command>systemd-coredump</command>
  37     executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
  38     second time in the <filename>systemd-coredump@.service</filename> to actually write the data to
  39     the journal.</para>
  40
  41     <para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs
  42     in privileged mode, and will connect to the socket created by the
  43     <filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
  44     <filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
  45     <filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename>
  46     are helper units which do the actual processing of core dumps and are subject to normal service
  47     management.</para>
  48
  49     <para>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
  50     for further processing, for example in
  51     <citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
  52     </para>
  53
  54     <para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
  55     if possible to the journal and store the core dump itself in an external file in
  56     <filename>/var/lib/systemd/coredump</filename>.</para>
  57
  58     <para>The behavior of a specific program upon reception of a signal is governed by a few
  59     factors which are described in detail in
  60     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  61     In particular, the core dump will only be processed when the related resource limits are sufficient.
  62     </para>
  63
  64     <para>It is also possible to invoke <command>systemd-coredump</command> with
  65     <option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects
  66     a journal entry in the journal
  67     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
  68     on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
  69     metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append
  70     additional metadata fields in the same way it does for core dumps received from the kernel. In
  71     this mode, no core dump is stored in the journal.</para>
  72   </refsect1>
  73
  74   <refsect1>
  75     <title>Configuration</title>
  76     <para>For programs started by <command>systemd</command> process resource limits can be set by directive
  77     <varname>LimitCore=</varname>, see
  78     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  79     </para>
  80
  81     <para>In order to be used by the kernel to handle core dumps,
  82     <command>systemd-coredump</command> must be configured in
  83     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  84     parameter <varname>kernel.core_pattern</varname>. The syntax of this parameter is explained in
  85     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  86     systemd installs the file <filename>/usr/lib/sysctl.d/50-coredump.conf</filename> which configures
  87     <varname>kernel.core_pattern</varname> accordingly. This file may be masked or overridden to use a different
  88     setting following normal
  89     <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  90     rules. If the sysctl configuration is modified, it must be updated in the kernel before it
  91     takes effect, see
  92     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  93     and
  94     <citerefentry><refentrytitle>systemd-sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
  95     </para>
  96
  97     <para>In order to by used in the <option>--backtrace</option> mode, an appropriate backtrace
  98     handler must be installed on the sender side. For example, in case of
  99     <citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry>, this
 100     means a <varname>sys.excepthook</varname> must installed, see
 101     <ulink url="https://github.com/keszybz/systemd-coredump-python">systemd-coredump-python</ulink>.
 102     </para>
 103
 104     <para>The behavior of <command>systemd-coredump</command> itself is configured through the configuration file
 105     <filename>/etc/systemd/coredump.conf</filename> and corresponding snippets
 106     <filename>/etc/systemd/coredump.conf.d/*.conf</filename>, see
 107     <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. A new
 108     instance of <command>systemd-coredump</command> is invoked upon receiving every core dump. Therefore, changes
 109     in these files will take effect the next time a core dump is received.</para>
 110
 111     <para>Resources used by core dump files are restricted in two ways. Parameters like maximum size of acquired
 112     core dumps and files can be set in files <filename>/etc/systemd/coredump.conf</filename> and snippets mentioned
 113     above. In addition the storage time of core dump files is restricted by <command>systemd-tmpfiles</command>,
 114     corresponding settings are by default in <filename>/usr/lib/tmpfiles.d/systemd.conf</filename>.</para>
 115
 116     <refsect2>
 117       <title>Disabling coredump processing</title>
 118
 119       <para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>,
 120       set <programlisting>Storage=none
 121 ProcessSizeMax=0</programlisting> in
 122       <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 123       </para>
 124     </refsect2>
 125   </refsect1>
 126
 127   <refsect1>
 128     <title>Usage</title>
 129     <para>Data stored in the journal can be viewed with
 130     <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 131     as usual.
 132     <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 133     can be used to retrieve saved core dumps independent of their location, to display information and to process
 134     them e.g. by passing to the GNU debugger (gdb).</para>
 135   </refsect1>
 136
 137   <refsect1>
 138     <title>See Also</title>
 139     <para>
 140       <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 141       <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 142       <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 143       <citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 144       <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 145       <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 146       <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 147     </para>
 148   </refsect1>
 149 </refentry>