1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
|
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
-->
<refentry id="systemd-coredump" conditional='ENABLE_COREDUMP'
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>systemd-coredump</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-coredump</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-coredump</refname>
<refname>systemd-coredump.socket</refname>
<refname>systemd-coredump@.service</refname>
<refpurpose>Acquire, save and process core dumps</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/usr/lib/systemd/systemd-coredump</filename></para>
<para><filename>/usr/lib/systemd/systemd-coredump</filename> <option>--backtrace</option></para>
<para><filename>systemd-coredump@.service</filename></para>
<para><filename>systemd-coredump.socket</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-coredump@.service</filename> is a system service that can acquire core
dumps from the kernel and handle them in various ways. The <command>systemd-coredump</command>
executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
second time in the <filename>systemd-coredump@.service</filename> to actually write the data to
the journal.</para>
<para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs
in privileged mode, and will connect to the socket created by the
<filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
<filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
<filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename>
are helper units which do the actual processing of core dumps and are subject to normal service
management.</para>
<para>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
for further processing, for example in
<citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
</para>
<para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
if possible to the journal and store the core dump itself in an external file in
<filename>/var/lib/systemd/coredump</filename>.</para>
<para>The behavior of a specific program upon reception of a signal is governed by a few
factors which are described in detail in
<citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
In particular, the core dump will only be processed when the related resource limits are sufficient.
</para>
<para>It is also possible to invoke <command>systemd-coredump</command> with
<option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects
a journal entry in the journal
<ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append
additional metadata fields in the same way it does for core dumps received from the kernel. In
this mode, no core dump is stored in the journal.</para>
</refsect1>
<refsect1>
<title>Configuration</title>
<para>For programs started by <command>systemd</command> process resource limits can be set by directive
<varname>LimitCore=</varname>, see
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
<para>In order to be used by the kernel to handle core dumps,
<command>systemd-coredump</command> must be configured in
<citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
parameter <varname>kernel.core_pattern</varname>. The syntax of this parameter is explained in
<citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
systemd installs the file <filename>/usr/lib/sysctl.d/50-coredump.conf</filename> which configures
<varname>kernel.core_pattern</varname> accordingly. This file may be masked or overridden to use a different
setting following normal
<citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
rules. If the sysctl configuration is modified, it must be updated in the kernel before it
takes effect, see
<citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd-sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
</para>
<para>In order to by used in the <option>--backtrace</option> mode, an appropriate backtrace
handler must be installed on the sender side. For example, in case of
<citerefentry project='die-net'><refentrytitle>python</refentrytitle><manvolnum>1</manvolnum></citerefentry>, this
means a <varname>sys.excepthook</varname> must installed, see
<ulink url="https://github.com/keszybz/systemd-coredump-python">systemd-coredump-python</ulink>.
</para>
<para>The behavior of <command>systemd-coredump</command> itself is configured through the configuration file
<filename>/etc/systemd/coredump.conf</filename> and corresponding snippets
<filename>/etc/systemd/coredump.conf.d/*.conf</filename>, see
<citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. A new
instance of <command>systemd-coredump</command> is invoked upon receiving every core dump. Therefore, changes
in these files will take effect the next time a core dump is received.</para>
<para>Resources used by core dump files are restricted in two ways. Parameters like maximum size of acquired
core dumps and files can be set in files <filename>/etc/systemd/coredump.conf</filename> and snippets mentioned
above. In addition the storage time of core dump files is restricted by <command>systemd-tmpfiles</command>,
corresponding settings are by default in <filename>/usr/lib/tmpfiles.d/systemd.conf</filename>.</para>
<refsect2>
<title>Disabling coredump processing</title>
<para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>,
set <programlisting>Storage=none
ProcessSizeMax=0</programlisting> in
<citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
</refsect2>
</refsect1>
<refsect1>
<title>Usage</title>
<para>Data stored in the journal can be viewed with
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
as usual.
<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
can be used to retrieve saved core dumps independent of their location, to display information and to process
them e.g. by passing to the GNU debugger (gdb).</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
</para>
</refsect1>
</refentry>
|
