man/systemd-coredump.xml

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  10   Copyright 2014 Zbigniew Jędrzejewski-Szmek
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  25
  26 <refentry id="systemd-coredump" conditional='ENABLE_COREDUMP'
  27           xmlns:xi="http://www.w3.org/2001/XInclude">
  28
  29   <refentryinfo>
  30     <title>systemd-coredump</title>
  31     <productname>systemd</productname>
  32
  33     <authorgroup>
  34       <author>
  35         <contrib>Developer</contrib>
  36         <firstname>Lennart</firstname>
  37         <surname>Poettering</surname>
  38         <email>lennart@poettering.net</email>
  39       </author>
  40     </authorgroup>
  41   </refentryinfo>
  42
  43   <refmeta>
  44     <refentrytitle>systemd-coredump</refentrytitle>
  45     <manvolnum>8</manvolnum>
  46   </refmeta>
  47
  48   <refnamediv>
  49     <refname>systemd-coredump</refname>
  50     <refname>systemd-coredump.socket</refname>
  51     <refname>systemd-coredump@.service</refname>
  52     <refpurpose>Acquire, save and process core dumps</refpurpose>
  53   </refnamediv>
  54
  55   <refsynopsisdiv>
  56     <para><filename>/usr/lib/systemd/systemd-coredump</filename></para>
  57     <para><filename>/usr/lib/systemd/systemd-coredump</filename> <option>--backtrace</option></para>
  58     <para><filename>systemd-coredump@.service</filename></para>
  59     <para><filename>systemd-coredump.socket</filename></para>
  60   </refsynopsisdiv>
  61
  62   <refsect1>
  63     <title>Description</title>
  64     <para><filename>systemd-coredump@.service</filename> is a system service that can acquire core
  65     dumps from the kernel and handle them in various ways. The <command>systemd-coredump</command>
  66     executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
  67     second time in the <filename>systemd-coredump@.service</filename> to actually write the data to
  68     the journal.</para>
  69
  70     <para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs
  71     in privileged mode, and will connect to the socket created by the
  72     <filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
  73     <filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
  74     <filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename>
  75     are helper units which do the actual processing of core dumps and are subject to normal service
  76     management.</para>
  77
  78     <para>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
  79     for further processing, for example in
  80     <citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
  81     </para>
  82
  83     <para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
  84     if possible to the journal and store the core dump itself in an external file in
  85     <filename>/var/lib/systemd/coredump</filename>.</para>
  86
  87     <para>The behavior of a specific program upon reception of a signal is governed by a few
  88     factors which are described in detail in
  89     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  90     In particular, the core dump will only be processed when the related resource limits are sufficient.
  91     </para>
  92
  93     <para>It is also possible to invoke <command>systemd-coredump</command> with
  94     <option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects
  95     a journal entry in the journal
  96     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
  97     on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
  98     metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append
  99     additional metadata fields in the same way it does for core dumps received from the kernel. In
 100     this mode, no core dump is stored in the journal.</para>
 101   </refsect1>
 102
 103   <refsect1>
 104     <title>Configuration</title>
 105     <para>For programs started by <command>systemd</command> process resource limits can be set by directive
 106     <varname>LimitCore=</varname>, see
 107     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 108     </para>
 109
 110     <para>In order to be used by the kernel to handle core dumps,
 111     <command>systemd-coredump</command> must be configured in
 112     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 113     parameter <varname>kernel.core_pattern</varname>. The syntax of this parameter is explained in
 114     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 115     systemd installs the file <filename>/usr/lib/sysctl.d/50-coredump.conf</filename> which configures
 116     <varname>kernel.core_pattern</varname> accordingly. This file may be masked or overridden to use a different
 117     setting following normal
 118     <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 119     rules. If the sysctl configuration is modified, it must be updated in the kernel before it
 120     takes effect, see
 121     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 122     and
 123     <citerefentry><refentrytitle>systemd-sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 124     </para>
 125
 126     <para>In order to by used in the <option>--backtrace</option> mode, an appropriate backtrace
 127     handler must be installed on the sender side. For example, in case of
 128     <citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry>, this
 129     means a <varname>sys.excepthook</varname> must installed, see
 130     <ulink url="https://github.com/keszybz/systemd-coredump-python">systemd-coredump-python</ulink>.
 131     </para>
 132
 133     <para>The behavior of <command>systemd-coredump</command> itself is configured through the configuration file
 134     <filename>/etc/systemd/coredump.conf</filename> and corresponding snippets
 135     <filename>/etc/systemd/coredump.conf.d/*.conf</filename>, see
 136     <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. A new
 137     instance of <command>systemd-coredump</command> is invoked upon receiving every core dump. Therefore, changes
 138     in these files will take effect the next time a core dump is received.</para>
 139
 140     <para>Resources used by core dump files are restricted in two ways. Parameters like maximum size of acquired
 141     core dumps and files can be set in files <filename>/etc/systemd/coredump.conf</filename> and snippets mentioned
 142     above. In addition the storage time of core dump files is restricted by <command>systemd-tmpfiles</command>,
 143     corresponding settings are by default in <filename>/usr/lib/tmpfiles.d/systemd.conf</filename>.</para>
 144   </refsect1>
 145
 146   <refsect1>
 147     <title>Usage</title>
 148     <para>Data stored in the journal can be viewed with
 149     <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 150     as usual.
 151     <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 152     can be used to retrieve saved core dumps independent of their location, to display information and to process
 153     them e.g. by passing to the GNU debugger (gdb).</para>
 154   </refsect1>
 155
 156   <refsect1>
 157     <title>See Also</title>
 158     <para>
 159       <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 160       <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 161       <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 162       <citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 163       <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 164       <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 165       <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 166     </para>
 167   </refsect1>
 168 </refentry>