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[elogind.git] / man / systemd-journald.service.xml
1 <?xml version='1.0'?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4
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8   Copyright 2010 Lennart Poettering
9
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22 -->
23
24 <refentry id="systemd-journald.service">
25
26         <refentryinfo>
27                 <title>systemd-journald.service</title>
28                 <productname>systemd</productname>
29
30                 <authorgroup>
31                         <author>
32                                 <contrib>Developer</contrib>
33                                 <firstname>Lennart</firstname>
34                                 <surname>Poettering</surname>
35                                 <email>lennart@poettering.net</email>
36                         </author>
37                 </authorgroup>
38         </refentryinfo>
39
40         <refmeta>
41                 <refentrytitle>systemd-journald.service</refentrytitle>
42                 <manvolnum>8</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>systemd-journald.service</refname>
47                 <refname>systemd-journald.socket</refname>
48                 <refname>systemd-journald-dev-log.socket</refname>
49                 <refname>systemd-journald</refname>
50                 <refpurpose>Journal service</refpurpose>
51         </refnamediv>
52
53         <refsynopsisdiv>
54                 <para><filename>systemd-journald.service</filename></para>
55                 <para><filename>systemd-journald.socket</filename></para>
56                 <para><filename>systemd-journald-dev-log.socket</filename></para>
57                 <para><filename>/usr/lib/systemd/systemd-journald</filename></para>
58         </refsynopsisdiv>
59
60         <refsect1>
61                 <title>Description</title>
62
63                 <para><filename>systemd-journald</filename> is a
64                 system service that collects and stores logging data.
65                 It creates and maintains structured, indexed journals
66                 based on logging information that is received from a
67                 variety of sources:</para>
68
69                 <itemizedlist>
70                         <listitem><para>Kernel log messages, via kmsg</para></listitem>
71
72                         <listitem><para>Simple system log messages, via the
73                         libc <citerefentry
74                         project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
75                         call</para></listitem>
76
77                         <listitem><para>Structured system log messages via the
78                         native Journal API, see
79                         <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry></para></listitem>
80
81                         <listitem><para>Standard output and
82                         standard error of system
83                         services</para></listitem>
84
85                         <listitem><para>Audit records, via the audit subsystem</para></listitem>
86                 </itemizedlist>
87
88                 <para>The daemon will implicitly collect numerous
89                 metadata fields for each log messages in a secure and
90                 unfakeable way. See
91                 <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
92                 for more information about the collected metadata.
93                 </para>
94
95                 <para>Log data collected by the journal is primarily
96                 text-based but can also include binary data where
97                 necessary. All objects stored in the journal can be up
98                 to 2^64-1 bytes in size.</para>
99
100                 <para>By default, the journal stores log data in
101                 <filename>/run/log/journal/</filename>. Since
102                 <filename>/run/</filename> is volatile, log data is
103                 lost at reboot. To make the data persistent, it
104                 is sufficient to create
105                 <filename>/var/log/journal/</filename> where
106                 <filename>systemd-journald</filename> will then store
107                 the data.</para>
108
109                 <para><filename>systemd-journald</filename> will
110                 forward all received log messages to the <constant>AF_UNIX</constant>/<constant>SOCK_DGRAM</constant> socket
111                 <filename>/run/systemd/journal/syslog</filename>, if it exists, which
112                 may be used by Unix syslog daemons to process the data
113                 further.</para>
114
115                 <para>See
116                 <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
117                 for information about the configuration of this
118                 service.</para>
119         </refsect1>
120
121         <refsect1>
122                 <title>Signals</title>
123
124                 <variablelist>
125                         <varlistentry>
126                                 <term>SIGUSR1</term>
127
128                                 <listitem><para>Request that journal
129                                 data from <filename>/run/</filename>
130                                 is flushed to
131                                 <filename>/var/</filename> in order to
132                                 make it persistent (if this is
133                                 enabled). This must be used after
134                                 <filename>/var/</filename> is mounted,
135                                 as otherwise log data from
136                                 <filename>/run</filename> is never
137                                 flushed to <filename>/var</filename>
138                                 regardless of the
139                                 configuration.</para></listitem>
140                         </varlistentry>
141
142                         <varlistentry>
143                                 <term>SIGUSR2</term>
144
145                                 <listitem><para>Request immediate
146                                 rotation of the journal
147                                 files.</para></listitem>
148                         </varlistentry>
149                 </variablelist>
150         </refsect1>
151
152         <refsect1>
153                 <title>Kernel Command Line</title>
154
155                 <para>A few configuration parameters from
156                 <filename>journald.conf</filename> may be overridden on
157                 the kernel command line:</para>
158
159                 <variablelist class='kernel-commandline-options'>
160                         <varlistentry>
161                                 <term><varname>systemd.journald.forward_to_syslog=</varname></term>
162                                 <term><varname>systemd.journald.forward_to_kmsg=</varname></term>
163                                 <term><varname>systemd.journald.forward_to_console=</varname></term>
164                                 <term><varname>systemd.journald.forward_to_wall=</varname></term>
165
166                                 <listitem><para>Enables/disables
167                                 forwarding of collected log messages
168                                 to syslog, the kernel log buffer, the
169                                 system console or wall.
170                                 </para>
171
172                                 <para>See
173                                 <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
174                                 for information about these settings.</para>
175                                 </listitem>
176
177                         </varlistentry>
178                 </variablelist>
179         </refsect1>
180
181         <refsect1>
182                 <title>Access Control</title>
183
184                 <para>Journal files are, by default, owned and readable
185                 by the <literal>systemd-journal</literal> system group
186                 but are not writable. Adding a user to this group thus
187                 enables her/him to read the journal files.</para>
188
189                 <para>By default, each logged in user will get her/his
190                 own set of journal files in
191                 <filename>/var/log/journal/</filename>. These files
192                 will not be owned by the user, however, in order to
193                 avoid that the user can write to them
194                 directly. Instead, file system ACLs are used to ensure
195                 the user gets read access only.</para>
196
197                 <para>Additional users and groups may be granted
198                 access to journal files via file system access control
199                 lists (ACL). Distributions and administrators may
200                 choose to grant read access to all members of the
201                 <literal>wheel</literal> and <literal>adm</literal>
202                 system groups with a command such as the
203                 following:</para>
204
205                 <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>
206
207                 <para>Note that this command will update the ACLs both
208                 for existing journal files and for future journal
209                 files created in the
210                 <filename>/var/log/journal/</filename>
211                 directory.</para>
212         </refsect1>
213
214         <refsect1>
215                 <title>Files</title>
216
217                 <variablelist>
218                         <varlistentry>
219                                 <term><filename>/etc/systemd/journald.conf</filename></term>
220
221                                 <listitem><para>Configure
222                                 <command>systemd-journald</command>
223                                 behaviour. See
224                                 <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
225                                 </para></listitem>
226                         </varlistentry>
227
228                         <varlistentry>
229                                 <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
230                                 <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
231                                 <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
232                                 <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
233
234                                 <listitem><para><command>systemd-journald</command>
235                                 writes entries to files in
236                                 <filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename>
237                                 or
238                                 <filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename>
239                                 with the <literal>.journal</literal>
240                                 suffix. If the daemon is stopped
241                                 uncleanly, or if the files are found
242                                 to be corrupted, they are renamed
243                                 using the <literal>.journal~</literal>
244                                 suffix, and
245                                 <command>systemd-journald</command>
246                                 starts writing to a new
247                                 file. <filename>/run</filename> is
248                                 used when
249                                 <filename>/var/log/journal</filename>
250                                 is not available, or when
251                                 <option>Storage=volatile</option> is
252                                 set in the
253                                 <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
254                                 configuration file.
255                                 </para></listitem>
256                         </varlistentry>
257                 </variablelist>
258         </refsect1>
259
260         <refsect1>
261                 <title>See Also</title>
262                 <para>
263                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
264                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
265                         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
266                         <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
267                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
268                         <citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
269                         <citerefentry><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
270                         <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
271                         <command>pydoc systemd.journal</command>.
272                 </para>
273         </refsect1>
274
275 </refentry>