man/systemd-coredump.xml

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