man/systemd-coredump.xml

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   8   Copyright © 2014 Zbigniew Jędrzejewski-Szmek
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  10
  11 <refentry id="systemd-coredump" conditional='ENABLE_COREDUMP'
  12           xmlns:xi="http://www.w3.org/2001/XInclude">
  13
  14   <refentryinfo>
  15     <title>systemd-coredump</title>
  16     <productname>systemd</productname>
  17
  18     <authorgroup>
  19       <author>
  20         <contrib>Developer</contrib>
  21         <firstname>Lennart</firstname>
  22         <surname>Poettering</surname>
  23         <email>lennart@poettering.net</email>
  24       </author>
  25     </authorgroup>
  26   </refentryinfo>
  27
  28   <refmeta>
  29     <refentrytitle>systemd-coredump</refentrytitle>
  30     <manvolnum>8</manvolnum>
  31   </refmeta>
  32
  33   <refnamediv>
  34     <refname>systemd-coredump</refname>
  35     <refname>systemd-coredump.socket</refname>
  36     <refname>systemd-coredump@.service</refname>
  37     <refpurpose>Acquire, save and process core dumps</refpurpose>
  38   </refnamediv>
  39
  40   <refsynopsisdiv>
  41     <para><filename>/usr/lib/systemd/systemd-coredump</filename></para>
  42     <para><filename>/usr/lib/systemd/systemd-coredump</filename> <option>--backtrace</option></para>
  43     <para><filename>systemd-coredump@.service</filename></para>
  44     <para><filename>systemd-coredump.socket</filename></para>
  45   </refsynopsisdiv>
  46
  47   <refsect1>
  48     <title>Description</title>
  49     <para><filename>systemd-coredump@.service</filename> is a system service that can acquire core
  50     dumps from the kernel and handle them in various ways. The <command>systemd-coredump</command>
  51     executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
  52     second time in the <filename>systemd-coredump@.service</filename> to actually write the data to
  53     the journal.</para>
  54
  55     <para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs
  56     in privileged mode, and will connect to the socket created by the
  57     <filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
  58     <filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
  59     <filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename>
  60     are helper units which do the actual processing of core dumps and are subject to normal service
  61     management.</para>
  62
  63     <para>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
  64     for further processing, for example in
  65     <citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
  66     </para>
  67
  68     <para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
  69     if possible to the journal and store the core dump itself in an external file in
  70     <filename>/var/lib/systemd/coredump</filename>.</para>
  71
  72     <para>The behavior of a specific program upon reception of a signal is governed by a few
  73     factors which are described in detail in
  74     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  75     In particular, the core dump will only be processed when the related resource limits are sufficient.
  76     </para>
  77
  78     <para>It is also possible to invoke <command>systemd-coredump</command> with
  79     <option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects
  80     a journal entry in the journal
  81     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
  82     on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
  83     metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append
  84     additional metadata fields in the same way it does for core dumps received from the kernel. In
  85     this mode, no core dump is stored in the journal.</para>
  86   </refsect1>
  87
  88   <refsect1>
  89     <title>Configuration</title>
  90     <para>For programs started by <command>systemd</command> process resource limits can be set by directive
  91     <varname>LimitCore=</varname>, see
  92     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  93     </para>
  94
  95     <para>In order to be used by the kernel to handle core dumps,
  96     <command>systemd-coredump</command> must be configured in
  97     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  98     parameter <varname>kernel.core_pattern</varname>. The syntax of this parameter is explained in
  99     <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 100     systemd installs the file <filename>/usr/lib/sysctl.d/50-coredump.conf</filename> which configures
 101     <varname>kernel.core_pattern</varname> accordingly. This file may be masked or overridden to use a different
 102     setting following normal
 103     <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 104     rules. If the sysctl configuration is modified, it must be updated in the kernel before it
 105     takes effect, see
 106     <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 107     and
 108     <citerefentry><refentrytitle>systemd-sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 109     </para>
 110
 111     <para>In order to by used in the <option>--backtrace</option> mode, an appropriate backtrace
 112     handler must be installed on the sender side. For example, in case of
 113     <citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry>, this
 114     means a <varname>sys.excepthook</varname> must installed, see
 115     <ulink url="https://github.com/keszybz/systemd-coredump-python">systemd-coredump-python</ulink>.
 116     </para>
 117
 118     <para>The behavior of <command>systemd-coredump</command> itself is configured through the configuration file
 119     <filename>/etc/systemd/coredump.conf</filename> and corresponding snippets
 120     <filename>/etc/systemd/coredump.conf.d/*.conf</filename>, see
 121     <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. A new
 122     instance of <command>systemd-coredump</command> is invoked upon receiving every core dump. Therefore, changes
 123     in these files will take effect the next time a core dump is received.</para>
 124
 125     <para>Resources used by core dump files are restricted in two ways. Parameters like maximum size of acquired
 126     core dumps and files can be set in files <filename>/etc/systemd/coredump.conf</filename> and snippets mentioned
 127     above. In addition the storage time of core dump files is restricted by <command>systemd-tmpfiles</command>,
 128     corresponding settings are by default in <filename>/usr/lib/tmpfiles.d/systemd.conf</filename>.</para>
 129
 130     <refsect2>
 131       <title>Disabling coredump processing</title>
 132
 133       <para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>,
 134       set <programlisting>Storage=none
 135 ProcessSizeMax=0</programlisting> in
 136       <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 137       </para>
 138     </refsect2>
 139   </refsect1>
 140
 141   <refsect1>
 142     <title>Usage</title>
 143     <para>Data stored in the journal can be viewed with
 144     <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 145     as usual.
 146     <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 147     can be used to retrieve saved core dumps independent of their location, to display information and to process
 148     them e.g. by passing to the GNU debugger (gdb).</para>
 149   </refsect1>
 150
 151   <refsect1>
 152     <title>See Also</title>
 153     <para>
 154       <citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 155       <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 156       <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 157       <citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 158       <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 159       <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 160       <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 161     </para>
 162   </refsect1>
 163 </refentry>