man/systemd-coredump.xml

   1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2014 Zbigniew Jędrzejewski-Szmek
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd-coredump" conditional='ENABLE_COREDUMP'
  25           xmlns:xi="http://www.w3.org/2001/XInclude">
  26
  27   <refentryinfo>
  28     <title>systemd-coredump</title>
  29     <productname>systemd</productname>
  30
  31     <authorgroup>
  32       <author>
  33         <contrib>Developer</contrib>
  34         <firstname>Lennart</firstname>
  35         <surname>Poettering</surname>
  36         <email>lennart@poettering.net</email>
  37       </author>
  38     </authorgroup>
  39   </refentryinfo>
  40
  41   <refmeta>
  42     <refentrytitle>systemd-coredump</refentrytitle>
  43     <manvolnum>8</manvolnum>
  44   </refmeta>
  45
  46   <refnamediv>
  47     <refname>systemd-coredump</refname>
  48     <refname>systemd-coredump.socket</refname>
  49     <refname>systemd-coredump@.service</refname>
  50     <refpurpose>Acquire, save and process core dumps</refpurpose>
  51   </refnamediv>
  52
  53   <refsynopsisdiv>
  54     <para><filename>/usr/lib/systemd/systemd-coredump</filename></para>
  55     <para><filename>/usr/lib/systemd/systemd-coredump</filename> <option>--backtrace</option></para>
  56     <para><filename>systemd-coredump@.service</filename></para>
  57     <para><filename>systemd-coredump.socket</filename></para>
  58   </refsynopsisdiv>
  59
  60   <refsect1>
  61     <title>Description</title>
  62     <para><filename>systemd-coredump@.service</filename> is a system service that can acquire core
  63     dumps from the kernel and handle them in various ways. The <command>systemd-coredump</command>
  64     executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
  65     second time in the <filename>systemd-coredump@.service</filename> to actually write the data to
  66     the journal.</para>
  67
  68     <para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs
  69     in privileged mode, and will connect to the socket created by the
  70     <filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
  71     <filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
  72     <filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename>
  73     are helper units which do the actual processing of core dumps and are subject to normal service
  74     management.</para>
  75
  76     <para>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
  77     for further processing, for example in
  78     <citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
  79     </para>
  80
  81     <para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
  82     if possible to the journal and store the core dump itself in an external file in
  83     <filename>/var/lib/systemd/coredump</filename>.</para>
  84
  85     <para>The behavior of a specific program upon reception of a signal is governed by a few
  86     factors which are described in detail in
  87     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  88     In particular, the core dump will only be processed when the related resource limits are sufficient.
  89     </para>
  90
  91     <para>It is also possible to invoke <command>systemd-coredump</command> with
  92     <option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects
  93     a journal entry in the journal
  94     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
  95     on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
  96     metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append
  97     additional metadata fields in the same way it does for core dumps received from the kernel. In
  98     this mode, no core dump is stored in the journal.</para>
  99   </refsect1>
 100
 101   <refsect1>
 102     <title>Configuration</title>
 103     <para>For programs started by <command>systemd</command> process resource limits can be set by directive
 104     <varname>LimitCore=</varname>, see
 105     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 106     </para>
 107
 108     <para>In order to be used by the kernel to handle core dumps,
 109     <command>systemd-coredump</command> must be configured in
 110     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 111     parameter <varname>kernel.core_pattern</varname>. The syntax of this parameter is explained in
 112     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 113     Systemd installs the file <filename>/usr/lib/sysctl.d/50-coredump.conf</filename> which configures
 114     <varname>kernel.core_pattern</varname> accordingly. This file may be masked or overridden to use a different
 115     setting following normal
 116     <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 117     rules. If the sysctl configuration is modified, it must be updated in the kernel before it
 118     takes effect, see
 119     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 120     and
 121     <citerefentry><refentrytitle>systemd-sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 122     </para>
 123
 124     <para>In order to by used in the <option>--backtrace</option> mode, an appropriate backtrace
 125     handler must be installed on the sender side. For example, in case of
 126     <citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry>, this
 127     means a <varname>sys.excepthook</varname> must installed, see
 128     <ulink url="https://github.com/keszybz/systemd-coredump-python">systemd-coredump-python</ulink>.
 129     </para>
 130
 131     <para>The behavior of <command>systemd-coredump</command> itself is configured through the configuration file
 132     <filename>/etc/systemd/coredump.conf</filename> and corresponding snippets
 133     <filename>/etc/systemd/coredump.conf.d/*.conf</filename>, see
 134     <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. A new
 135     instance of <command>systemd-coredump</command> is invoked upon receiving every core dump. Therefore, changes
 136     in these files will take effect the next time a core dump is received.</para>
 137
 138     <para>Resources used by core dump files are restricted in two ways. Parameters like maximum size of acquired
 139     core dumps and files can be set in files <filename>/etc/systemd/coredump.conf</filename> and snippets mentioned
 140     above. In addition the storage time of core dump files is restricted by <command>systemd-tmpfiles</command>,
 141     corresponding settings are by default in <filename>/usr/lib/tmpfiles.d/systemd.conf</filename>.</para>
 142   </refsect1>
 143
 144   <refsect1>
 145     <title>Usage</title>
 146     <para>Data stored in the journal can be viewed with
 147     <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 148     as usual.
 149     <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 150     can be used to retrieve saved core dumps independent of their location, to display information and to process
 151     them e.g. by passing to the GNU debugger (gdb).</para>
 152   </refsect1>
 153
 154   <refsect1>
 155     <title>See Also</title>
 156     <para>
 157       <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 158       <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 159       <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 160       <citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 161       <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 162       <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 163       <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 164     </para>
 165   </refsect1>
 166 </refentry>