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01cf0ca8 | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
db9ecf05 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
01cf0ca8 | 5 | |
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6 | <refentry id="systemd-journald.service" |
7 | xmlns:xi="http://www.w3.org/2001/XInclude"> | |
01cf0ca8 | 8 | |
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9 | <refentryinfo> |
10 | <title>systemd-journald.service</title> | |
11 | <productname>systemd</productname> | |
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12 | </refentryinfo> |
13 | ||
14 | <refmeta> | |
15 | <refentrytitle>systemd-journald.service</refentrytitle> | |
16 | <manvolnum>8</manvolnum> | |
17 | </refmeta> | |
18 | ||
19 | <refnamediv> | |
20 | <refname>systemd-journald.service</refname> | |
21 | <refname>systemd-journald.socket</refname> | |
22 | <refname>systemd-journald-dev-log.socket</refname> | |
37b7affe | 23 | <refname>systemd-journald-audit.socket</refname> |
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24 | <refname>systemd-journald@.service</refname> |
25 | <refname>systemd-journald@.socket</refname> | |
26 | <refname>systemd-journald-varlink@.socket</refname> | |
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27 | <refname>systemd-journald</refname> |
28 | <refpurpose>Journal service</refpurpose> | |
29 | </refnamediv> | |
30 | ||
31 | <refsynopsisdiv> | |
32 | <para><filename>systemd-journald.service</filename></para> | |
33 | <para><filename>systemd-journald.socket</filename></para> | |
34 | <para><filename>systemd-journald-dev-log.socket</filename></para> | |
37b7affe | 35 | <para><filename>systemd-journald-audit.socket</filename></para> |
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36 | <para><filename>systemd-journald@.service</filename></para> |
37 | <para><filename>systemd-journald@.socket</filename></para> | |
38 | <para><filename>systemd-journald-varlink@.socket</filename></para> | |
12b42c76 | 39 | <para><filename>/usr/lib/systemd/systemd-journald</filename></para> |
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40 | </refsynopsisdiv> |
41 | ||
42 | <refsect1> | |
43 | <title>Description</title> | |
44 | ||
45 | <para><filename>systemd-journald</filename> is a system service | |
46 | that collects and stores logging data. It creates and maintains | |
47 | structured, indexed journals based on logging information that is | |
48 | received from a variety of sources:</para> | |
49 | ||
50 | <itemizedlist> | |
51 | <listitem><para>Kernel log messages, via kmsg</para></listitem> | |
52 | ||
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53 | <listitem><para>Simple system log messages, via the <filename>libc</filename> <citerefentry |
54 | project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
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55 | call</para></listitem> |
56 | ||
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57 | <listitem><para>Structured system log messages via the native Journal API, see |
58 | <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
59 | and <ulink url="https://systemd.io/JOURNAL_NATIVE_PROTOCOL">Native Journal | |
60 | Protocol</ulink></para></listitem> | |
798d3a52 | 61 | |
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62 | <listitem><para>Standard output and standard error of service units. For further details see |
63 | below.</para></listitem> | |
798d3a52 | 64 | |
157148d6 | 65 | <listitem><para>Audit records, originating from the kernel audit subsystem</para></listitem> |
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66 | </itemizedlist> |
67 | ||
68 | <para>The daemon will implicitly collect numerous metadata fields | |
69 | for each log messages in a secure and unfakeable way. See | |
70 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
71 | for more information about the collected metadata. | |
72 | </para> | |
73 | ||
fc5f5706 | 74 | <para>Log data collected by the journal is primarily text-based but can also include binary data where |
a2968e83 | 75 | necessary. Individual fields making up a log record stored in the journal may be up to 2⁶⁴-1 bytes in size.</para> |
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76 | |
77 | <para>The journal service stores log data either persistently below <filename>/var/log/journal</filename> or in a | |
78 | volatile way below <filename>/run/log/journal/</filename> (in the latter case it is lost at reboot). By default, log | |
79 | data is stored persistently if <filename>/var/log/journal/</filename> exists during boot, with an implicit fallback | |
80 | to volatile storage otherwise. Use <varname>Storage=</varname> in | |
81 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> to configure | |
82 | where log data is placed, independently of the existence of <filename>/var/log/journal/</filename>.</para> | |
83 | ||
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84 | <para>Note that journald will initially use volatile storage, until a call to |
85 | <command>journalctl --flush</command> (or sending <constant>SIGUSR1</constant> to journald) will cause | |
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86 | it to switch to persistent logging (under the conditions mentioned above). This is done automatically |
87 | on boot via <literal>systemd-journal-flush.service</literal>.</para> | |
88 | ||
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89 | <para>On systems where <filename>/var/log/journal/</filename> does not exist yet but where persistent logging is |
90 | desired (and the default <filename>journald.conf</filename> is used), it is sufficient to create the directory, and | |
91 | ensure it has the correct access modes and ownership:</para> | |
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92 | |
93 | <programlisting>mkdir -p /var/log/journal | |
94 | systemd-tmpfiles --create --prefix /var/log/journal</programlisting> | |
798d3a52 | 95 | |
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96 | <para>See |
97 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
98 | for information about the configuration of this service.</para> | |
99 | </refsect1> | |
100 | ||
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101 | <refsect1> |
102 | <title>Stream logging</title> | |
103 | ||
104 | <para>The systemd service manager invokes all service processes with standard output and standard error connected | |
105 | to the journal by default. This behaviour may be altered via the | |
106 | <varname>StandardOutput=</varname>/<varname>StandardError=</varname> unit file settings, see | |
107 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The | |
108 | journal converts the log byte stream received this way into individual log records, splitting the stream at newline | |
109 | (<literal>\n</literal>, ASCII <constant>10</constant>) and <constant>NUL</constant> bytes.</para> | |
110 | ||
111 | <para>If <filename>systemd-journald.service</filename> is stopped, the stream connections associated with all | |
112 | services are terminated. Further writes to those streams by the service will result in <constant>EPIPE</constant> | |
113 | errors. In order to react gracefully in this case it is recommended that programs logging to standard output/error | |
dcfaecc7 | 114 | ignore such errors. If the <constant>SIGPIPE</constant> UNIX signal handler is not blocked or turned off, such |
157148d6 | 115 | write attempts will also result in such process signals being generated, see |
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116 | <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>. |
117 | To mitigate this issue, systemd service manager explicitly turns off the <constant>SIGPIPE</constant> | |
118 | signal for all invoked processes by default (this may be changed for each unit individually via the | |
119 | <varname>IgnoreSIGPIPE=</varname> option, see | |
157148d6 | 120 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for |
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121 | details). After the standard output/standard error streams have been terminated they may not be recovered |
122 | until the services they are associated with are restarted. Note that during normal operation, | |
123 | <filename>systemd-journald.service</filename> stores copies of the file descriptors for those streams in | |
124 | the service manager. If <filename>systemd-journald.service</filename> is restarted using | |
125 | <command>systemctl restart</command> or equivalent operation instead of a pair of separate | |
126 | <command>systemctl stop</command> and <command>systemctl start</command> commands (or equivalent | |
127 | operations), these stream connections are not terminated and survive the restart. It is thus safe to | |
128 | restart <filename>systemd-journald.service</filename>, but stopping it is not recommended.</para> | |
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129 | |
130 | <para>Note that the log record metadata for records transferred via such standard output/error streams reflect the | |
131 | metadata of the peer the stream was originally created for. If the stream connection is passed on to other | |
132 | processes (such as further child processes forked off the main service process), the log records will not reflect | |
133 | their metadata, but will continue to describe the original process. This is different from the other logging | |
134 | transports listed above, which are inherently record based and where the metadata is always associated with the | |
135 | individual record.</para> | |
136 | ||
dcfaecc7 | 137 | <para>In addition to the implicit standard output/error logging of services, stream logging is also available |
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138 | via the <citerefentry><refentrytitle>systemd-cat</refentrytitle><manvolnum>1</manvolnum></citerefentry> command |
139 | line tool.</para> | |
140 | ||
ec20fe5f | 141 | <para>Currently, the number of parallel log streams <filename>systemd-journald</filename> will accept is limited to |
dcfaecc7 | 142 | 4096. When this limit is reached further log streams may be established but will receive |
ec20fe5f | 143 | <constant>EPIPE</constant> right from the beginning.</para> |
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144 | </refsect1> |
145 | ||
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146 | <refsect1> |
147 | <title>Journal Namespaces</title> | |
148 | ||
149 | <para>Journal 'namespaces' are both a mechanism for logically isolating the log stream of projects | |
150 | consisting of one or more services from the rest of the system and a mechanism for improving | |
151 | performance. Multiple journal namespaces may exist simultaneously, each defining its own, independent log | |
152 | stream managed by its own instance of <command>systemd-journald</command>. Namespaces are independent of | |
153 | each other, both in the data store and in the IPC interface. By default only a single 'default' namespace | |
154 | exists, managed by <filename>systemd-journald.service</filename> (and its associated socket | |
155 | units). Additional namespaces are created by starting an instance of the | |
156 | <filename>systemd-journald@.service</filename> service template. The instance name is the namespace | |
157 | identifier, which is a short string used for referencing the journal namespace. Service units may be | |
158 | assigned to a specific journal namespace through the <varname>LogNamespace=</varname> unit file setting, | |
159 | see <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for | |
160 | details. The <option>--namespace=</option> switch of | |
161 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> may be | |
162 | used to view the log stream of a specific namespace. If the switch is not used the log stream of the | |
163 | default namespace is shown, i.e. log data from other namespaces is not visible.</para> | |
164 | ||
165 | <para>Services associated with a specific log namespace may log via syslog, the native logging protocol | |
166 | of the journal and via stdout/stderr; the logging from all three transports is associated with the | |
167 | namespace.</para> | |
168 | ||
169 | <para>By default only the default namespace will collect kernel and audit log messages.</para> | |
170 | ||
171 | <para>The <command>systemd-journald</command> instance of the default namespace is configured through | |
172 | <filename>/etc/systemd/journald.conf</filename> (see below), while the other instances are configured | |
173 | through <filename>/etc/systemd/journald@<replaceable>NAMESPACE</replaceable>.conf</filename>. The journal | |
174 | log data for the default namespace is placed in | |
175 | <filename>/var/log/journal/<replaceable>MACHINE_ID</replaceable></filename> (see below) while the data | |
176 | for the other namespaces is located in | |
177 | <filename>/var/log/journal/<replaceable>MACHINE_ID</replaceable>.<replaceable>NAMESPACE</replaceable></filename>.</para> | |
178 | </refsect1> | |
179 | ||
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180 | <refsect1> |
181 | <title>Signals</title> | |
182 | ||
183 | <variablelist> | |
184 | <varlistentry> | |
185 | <term>SIGUSR1</term> | |
186 | ||
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187 | <listitem><para>Request that journal data from <filename>/run/</filename> is flushed to |
188 | <filename>/var/</filename> in order to make it persistent (if this is enabled). This must be used | |
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189 | after <filename>/var/</filename> is mounted, as otherwise log data from <filename>/run/</filename> is |
190 | never flushed to <filename>/var/</filename> regardless of the configuration. Use the | |
870a2d85 | 191 | <command>journalctl --flush</command> command to request flushing of the journal files, and wait for |
94b65516 | 192 | the operation to complete. See |
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193 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for |
194 | details.</para></listitem> | |
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195 | </varlistentry> |
196 | ||
197 | <varlistentry> | |
198 | <term>SIGUSR2</term> | |
199 | ||
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200 | <listitem><para>Request immediate rotation of the journal files. Use the <command>journalctl |
201 | --rotate</command> command to request journal file rotation, and wait for the operation to | |
202 | complete.</para></listitem> | |
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203 | </varlistentry> |
204 | ||
205 | <varlistentry> | |
206 | <term>SIGRTMIN+1</term> | |
207 | ||
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208 | <listitem><para>Request that all unwritten log data is written to disk. Use the <command>journalctl |
209 | --sync</command> command to trigger journal synchronization, and wait for the operation to | |
210 | complete.</para></listitem> | |
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211 | </varlistentry> |
212 | </variablelist> | |
213 | </refsect1> | |
214 | ||
215 | <refsect1> | |
216 | <title>Kernel Command Line</title> | |
217 | ||
218 | <para>A few configuration parameters from | |
219 | <filename>journald.conf</filename> may be overridden on the kernel | |
220 | command line:</para> | |
221 | ||
222 | <variablelist class='kernel-commandline-options'> | |
223 | <varlistentry> | |
224 | <term><varname>systemd.journald.forward_to_syslog=</varname></term> | |
225 | <term><varname>systemd.journald.forward_to_kmsg=</varname></term> | |
226 | <term><varname>systemd.journald.forward_to_console=</varname></term> | |
227 | <term><varname>systemd.journald.forward_to_wall=</varname></term> | |
228 | ||
229 | <listitem><para>Enables/disables forwarding of collected log | |
230 | messages to syslog, the kernel log buffer, the system console | |
231 | or wall. | |
232 | </para> | |
233 | ||
234 | <para>See | |
235 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
236 | for information about these settings.</para> | |
237 | </listitem> | |
238 | ||
239 | </varlistentry> | |
240 | </variablelist> | |
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241 | |
242 | <para>Note that these kernel command line options are only honoured by the default namespace, see | |
243 | above.</para> | |
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244 | </refsect1> |
245 | ||
246 | <refsect1> | |
247 | <title>Access Control</title> | |
248 | ||
249 | <para>Journal files are, by default, owned and readable by the | |
250 | <literal>systemd-journal</literal> system group but are not | |
f16eb8b0 | 251 | writable. Adding a user to this group thus enables them to read |
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252 | the journal files.</para> |
253 | ||
a1533ad7 AZ |
254 | <para>By default, each user, with a UID outside the range of system users, |
255 | dynamic service users, and the nobody user, will get their own set of | |
256 | journal files in <filename>/var/log/journal/</filename>. See | |
257 | <ulink url="https://systemd.io/UIDS-GIDS">Users, Groups, UIDs and GIDs on systemd systems</ulink> | |
258 | for more details about UID ranges. These journal | |
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259 | files will not be owned by the user, however, in order to avoid |
260 | that the user can write to them directly. Instead, file system | |
261 | ACLs are used to ensure the user gets read access only.</para> | |
262 | ||
263 | <para>Additional users and groups may be granted access to journal | |
264 | files via file system access control lists (ACL). Distributions | |
265 | and administrators may choose to grant read access to all members | |
266 | of the <literal>wheel</literal> and <literal>adm</literal> system | |
267 | groups with a command such as the following:</para> | |
268 | ||
269 | <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting> | |
270 | ||
271 | <para>Note that this command will update the ACLs both for | |
272 | existing journal files and for future journal files created in the | |
273 | <filename>/var/log/journal/</filename> directory.</para> | |
274 | </refsect1> | |
275 | ||
276 | <refsect1> | |
277 | <title>Files</title> | |
278 | ||
279 | <variablelist> | |
280 | <varlistentry> | |
12b42c76 | 281 | <term><filename>/etc/systemd/journald.conf</filename></term> |
798d3a52 | 282 | |
4bb890bc | 283 | <listitem><para>Configure <command>systemd-journald</command> behavior. See |
798d3a52 ZJS |
284 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. |
285 | </para></listitem> | |
286 | </varlistentry> | |
287 | ||
288 | <varlistentry> | |
289 | <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term> | |
290 | <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term> | |
291 | <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term> | |
292 | <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term> | |
293 | ||
4bb890bc | 294 | <listitem><para><command>systemd-journald</command> writes entries to files in |
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295 | <filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename> |
296 | or | |
297 | <filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename> | |
298 | with the <literal>.journal</literal> suffix. If the daemon is | |
299 | stopped uncleanly, or if the files are found to be corrupted, | |
300 | they are renamed using the <literal>.journal~</literal> | |
301 | suffix, and <command>systemd-journald</command> starts writing | |
3b121157 | 302 | to a new file. <filename>/run/</filename> is used when |
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303 | <filename>/var/log/journal</filename> is not available, or |
304 | when <option>Storage=volatile</option> is set in the | |
305 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
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306 | configuration file.</para> |
307 | ||
308 | <para>When <filename>systemd-journald</filename> ceases writing to a journal file, | |
309 | it will be renamed to <literal><replaceable>original-name</replaceable>@<replaceable>suffix.journal</replaceable></literal> | |
310 | (or <literal><replaceable>original-name</replaceable>@<replaceable>suffix.journal~</replaceable></literal>). | |
311 | Such files are "archived" and will not be written to any more.</para> | |
312 | ||
313 | <para>In general, it is safe to read or copy any journal file (active or archived). | |
314 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
315 | and the functions in the | |
316 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
317 | library should be able to read all entries that have been fully written.</para> | |
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318 | |
319 | <para><filename>systemd-journald</filename> will automatically remove the oldest | |
320 | archived journal files to limit disk use. See <varname>SystemMaxUse=</varname> | |
321 | and related settings in | |
322 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. | |
323 | </para></listitem> | |
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324 | </varlistentry> |
325 | ||
326 | <varlistentry> | |
327 | <term><filename>/dev/kmsg</filename></term> | |
328 | <term><filename>/dev/log</filename></term> | |
329 | <term><filename>/run/systemd/journal/dev-log</filename></term> | |
330 | <term><filename>/run/systemd/journal/socket</filename></term> | |
331 | <term><filename>/run/systemd/journal/stdout</filename></term> | |
332 | ||
efcbcd0d LP |
333 | <listitem><para>Sockets and other file node paths that <command>systemd-journald</command> will |
334 | listen on and are visible in the file system. In addition to these, | |
335 | <command>systemd-journald</command> can listen for audit events using <citerefentry | |
2aba7705 FB |
336 | project='man-pages'><refentrytitle>netlink</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
337 | depending on whether <literal>systemd-journald-audit.socket</literal> is enabled or | |
338 | not.</para></listitem> | |
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339 | </varlistentry> |
340 | </variablelist> | |
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341 | |
342 | <para>If journal namespacing is used these paths are slightly altered to include a namespace identifier, see above.</para> | |
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343 | </refsect1> |
344 | ||
345 | <refsect1> | |
346 | <title>See Also</title> | |
347 | <para> | |
348 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
349 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
350 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
351 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
352 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
353 | <citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>, | |
efcbcd0d | 354 | <citerefentry project='man-pages'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
01dc8e30 | 355 | <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
94b65516 | 356 | <command>pydoc systemd.journal</command> |
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357 | </para> |
358 | </refsect1> | |
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359 | |
360 | </refentry> |