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663996b3 | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
bb4f798a | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
e735f4d4 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
a032b68d | 4 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
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5 | |
6 | <refentry id="systemd-journald.service"> | |
7 | ||
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8 | <refentryinfo> |
9 | <title>systemd-journald.service</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>systemd-journald.service</refentrytitle> | |
15 | <manvolnum>8</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>systemd-journald.service</refname> | |
20 | <refname>systemd-journald.socket</refname> | |
21 | <refname>systemd-journald-dev-log.socket</refname> | |
db2df898 | 22 | <refname>systemd-journald-audit.socket</refname> |
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23 | <refname>systemd-journald@.service</refname> |
24 | <refname>systemd-journald@.socket</refname> | |
25 | <refname>systemd-journald-varlink@.socket</refname> | |
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26 | <refname>systemd-journald</refname> |
27 | <refpurpose>Journal service</refpurpose> | |
28 | </refnamediv> | |
29 | ||
30 | <refsynopsisdiv> | |
31 | <para><filename>systemd-journald.service</filename></para> | |
32 | <para><filename>systemd-journald.socket</filename></para> | |
33 | <para><filename>systemd-journald-dev-log.socket</filename></para> | |
db2df898 | 34 | <para><filename>systemd-journald-audit.socket</filename></para> |
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35 | <para><filename>systemd-journald@.service</filename></para> |
36 | <para><filename>systemd-journald@.socket</filename></para> | |
37 | <para><filename>systemd-journald-varlink@.socket</filename></para> | |
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38 | <para><filename>/usr/lib/systemd/systemd-journald</filename></para> |
39 | </refsynopsisdiv> | |
40 | ||
41 | <refsect1> | |
42 | <title>Description</title> | |
43 | ||
44 | <para><filename>systemd-journald</filename> is a system service | |
45 | that collects and stores logging data. It creates and maintains | |
46 | structured, indexed journals based on logging information that is | |
47 | received from a variety of sources:</para> | |
48 | ||
49 | <itemizedlist> | |
50 | <listitem><para>Kernel log messages, via kmsg</para></listitem> | |
51 | ||
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52 | <listitem><para>Simple system log messages, via the <filename>libc</filename> <citerefentry |
53 | project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
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54 | call</para></listitem> |
55 | ||
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56 | <listitem><para>Structured system log messages via the native Journal API, see |
57 | <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
58 | and <ulink url="https://systemd.io/JOURNAL_NATIVE_PROTOCOL">Native Journal | |
59 | Protocol</ulink></para></listitem> | |
e735f4d4 | 60 | |
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61 | <listitem><para>Standard output and standard error of service units. For further details see |
62 | below.</para></listitem> | |
e735f4d4 | 63 | |
f5e65279 | 64 | <listitem><para>Audit records, originating from the kernel audit subsystem</para></listitem> |
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65 | </itemizedlist> |
66 | ||
67 | <para>The daemon will implicitly collect numerous metadata fields | |
68 | for each log messages in a secure and unfakeable way. See | |
69 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
70 | for more information about the collected metadata. | |
71 | </para> | |
72 | ||
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73 | <para>Log data collected by the journal is primarily text-based but can also include binary data where |
74 | necessary. Individual fields making up a log record stored in the journal may be up to 2^64-1 bytes in size.</para> | |
75 | ||
76 | <para>The journal service stores log data either persistently below <filename>/var/log/journal</filename> or in a | |
77 | volatile way below <filename>/run/log/journal/</filename> (in the latter case it is lost at reboot). By default, log | |
78 | data is stored persistently if <filename>/var/log/journal/</filename> exists during boot, with an implicit fallback | |
79 | to volatile storage otherwise. Use <varname>Storage=</varname> in | |
80 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> to configure | |
81 | where log data is placed, independently of the existence of <filename>/var/log/journal/</filename>.</para> | |
e735f4d4 | 82 | |
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83 | <para>Note that journald will initially use volatile storage, until a call to |
84 | <command>journalctl --flush</command> (or sending <constant>SIGUSR1</constant> to journald) will cause | |
85 | it to switch to persistent logging (under the conditions mentioned above). This is done automatically | |
86 | on boot via <literal>systemd-journal-flush.service</literal>.</para> | |
87 | ||
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88 | <para>On systems where <filename>/var/log/journal/</filename> does not exist yet but where persistent logging is |
89 | desired (and the default <filename>journald.conf</filename> is used), it is sufficient to create the directory, and | |
90 | ensure it has the correct access modes and ownership:</para> | |
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91 | |
92 | <programlisting>mkdir -p /var/log/journal | |
93 | systemd-tmpfiles --create --prefix /var/log/journal</programlisting> | |
e735f4d4 | 94 | |
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95 | <para>See |
96 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
97 | for information about the configuration of this service.</para> | |
98 | </refsect1> | |
99 | ||
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100 | <refsect1> |
101 | <title>Stream logging</title> | |
102 | ||
103 | <para>The systemd service manager invokes all service processes with standard output and standard error connected | |
104 | to the journal by default. This behaviour may be altered via the | |
105 | <varname>StandardOutput=</varname>/<varname>StandardError=</varname> unit file settings, see | |
106 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The | |
107 | journal converts the log byte stream received this way into individual log records, splitting the stream at newline | |
108 | (<literal>\n</literal>, ASCII <constant>10</constant>) and <constant>NUL</constant> bytes.</para> | |
109 | ||
110 | <para>If <filename>systemd-journald.service</filename> is stopped, the stream connections associated with all | |
111 | services are terminated. Further writes to those streams by the service will result in <constant>EPIPE</constant> | |
112 | errors. In order to react gracefully in this case it is recommended that programs logging to standard output/error | |
52ad194e | 113 | ignore such errors. If the <constant>SIGPIPE</constant> UNIX signal handler is not blocked or turned off, such |
f5e65279 | 114 | write attempts will also result in such process signals being generated, see |
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115 | <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>. |
116 | To mitigate this issue, systemd service manager explicitly turns off the <constant>SIGPIPE</constant> | |
117 | signal for all invoked processes by default (this may be changed for each unit individually via the | |
118 | <varname>IgnoreSIGPIPE=</varname> option, see | |
f5e65279 | 119 | <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for |
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120 | details). After the standard output/standard error streams have been terminated they may not be recovered |
121 | until the services they are associated with are restarted. Note that during normal operation, | |
122 | <filename>systemd-journald.service</filename> stores copies of the file descriptors for those streams in | |
123 | the service manager. If <filename>systemd-journald.service</filename> is restarted using | |
124 | <command>systemctl restart</command> or equivalent operation instead of a pair of separate | |
125 | <command>systemctl stop</command> and <command>systemctl start</command> commands (or equivalent | |
126 | operations), these stream connections are not terminated and survive the restart. It is thus safe to | |
127 | restart <filename>systemd-journald.service</filename>, but stopping it is not recommended.</para> | |
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128 | |
129 | <para>Note that the log record metadata for records transferred via such standard output/error streams reflect the | |
130 | metadata of the peer the stream was originally created for. If the stream connection is passed on to other | |
131 | processes (such as further child processes forked off the main service process), the log records will not reflect | |
132 | their metadata, but will continue to describe the original process. This is different from the other logging | |
133 | transports listed above, which are inherently record based and where the metadata is always associated with the | |
134 | individual record.</para> | |
135 | ||
52ad194e | 136 | <para>In addition to the implicit standard output/error logging of services, stream logging is also available |
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137 | via the <citerefentry><refentrytitle>systemd-cat</refentrytitle><manvolnum>1</manvolnum></citerefentry> command |
138 | line tool.</para> | |
139 | ||
140 | <para>Currently, the number of parallel log streams <filename>systemd-journald</filename> will accept is limited to | |
52ad194e | 141 | 4096. When this limit is reached further log streams may be established but will receive |
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142 | <constant>EPIPE</constant> right from the beginning.</para> |
143 | </refsect1> | |
144 | ||
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145 | <refsect1> |
146 | <title>Journal Namespaces</title> | |
147 | ||
148 | <para>Journal 'namespaces' are both a mechanism for logically isolating the log stream of projects | |
149 | consisting of one or more services from the rest of the system and a mechanism for improving | |
150 | performance. Multiple journal namespaces may exist simultaneously, each defining its own, independent log | |
151 | stream managed by its own instance of <command>systemd-journald</command>. Namespaces are independent of | |
152 | each other, both in the data store and in the IPC interface. By default only a single 'default' namespace | |
153 | exists, managed by <filename>systemd-journald.service</filename> (and its associated socket | |
154 | units). Additional namespaces are created by starting an instance of the | |
155 | <filename>systemd-journald@.service</filename> service template. The instance name is the namespace | |
156 | identifier, which is a short string used for referencing the journal namespace. Service units may be | |
157 | assigned to a specific journal namespace through the <varname>LogNamespace=</varname> unit file setting, | |
158 | see <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for | |
159 | details. The <option>--namespace=</option> switch of | |
160 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> may be | |
161 | used to view the log stream of a specific namespace. If the switch is not used the log stream of the | |
162 | default namespace is shown, i.e. log data from other namespaces is not visible.</para> | |
163 | ||
164 | <para>Services associated with a specific log namespace may log via syslog, the native logging protocol | |
165 | of the journal and via stdout/stderr; the logging from all three transports is associated with the | |
166 | namespace.</para> | |
167 | ||
168 | <para>By default only the default namespace will collect kernel and audit log messages.</para> | |
169 | ||
170 | <para>The <command>systemd-journald</command> instance of the default namespace is configured through | |
171 | <filename>/etc/systemd/journald.conf</filename> (see below), while the other instances are configured | |
172 | through <filename>/etc/systemd/journald@<replaceable>NAMESPACE</replaceable>.conf</filename>. The journal | |
173 | log data for the default namespace is placed in | |
174 | <filename>/var/log/journal/<replaceable>MACHINE_ID</replaceable></filename> (see below) while the data | |
175 | for the other namespaces is located in | |
176 | <filename>/var/log/journal/<replaceable>MACHINE_ID</replaceable>.<replaceable>NAMESPACE</replaceable></filename>.</para> | |
177 | </refsect1> | |
178 | ||
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179 | <refsect1> |
180 | <title>Signals</title> | |
181 | ||
182 | <variablelist> | |
183 | <varlistentry> | |
184 | <term>SIGUSR1</term> | |
185 | ||
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186 | <listitem><para>Request that journal data from <filename>/run/</filename> is flushed to |
187 | <filename>/var/</filename> in order to make it persistent (if this is enabled). This must be used | |
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188 | after <filename>/var/</filename> is mounted, as otherwise log data from <filename>/run/</filename> is |
189 | never flushed to <filename>/var/</filename> regardless of the configuration. Use the | |
e1f67bc7 | 190 | <command>journalctl --flush</command> command to request flushing of the journal files, and wait for |
db2df898 | 191 | the operation to complete. See |
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192 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for |
193 | details.</para></listitem> | |
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194 | </varlistentry> |
195 | ||
196 | <varlistentry> | |
197 | <term>SIGUSR2</term> | |
198 | ||
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199 | <listitem><para>Request immediate rotation of the journal files. Use the <command>journalctl |
200 | --rotate</command> command to request journal file rotation, and wait for the operation to | |
201 | complete.</para></listitem> | |
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202 | </varlistentry> |
203 | ||
204 | <varlistentry> | |
205 | <term>SIGRTMIN+1</term> | |
206 | ||
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207 | <listitem><para>Request that all unwritten log data is written to disk. Use the <command>journalctl |
208 | --sync</command> command to trigger journal synchronization, and wait for the operation to | |
209 | complete.</para></listitem> | |
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210 | </varlistentry> |
211 | </variablelist> | |
212 | </refsect1> | |
213 | ||
214 | <refsect1> | |
215 | <title>Kernel Command Line</title> | |
216 | ||
217 | <para>A few configuration parameters from | |
218 | <filename>journald.conf</filename> may be overridden on the kernel | |
219 | command line:</para> | |
220 | ||
221 | <variablelist class='kernel-commandline-options'> | |
222 | <varlistentry> | |
223 | <term><varname>systemd.journald.forward_to_syslog=</varname></term> | |
224 | <term><varname>systemd.journald.forward_to_kmsg=</varname></term> | |
225 | <term><varname>systemd.journald.forward_to_console=</varname></term> | |
226 | <term><varname>systemd.journald.forward_to_wall=</varname></term> | |
227 | ||
228 | <listitem><para>Enables/disables forwarding of collected log | |
229 | messages to syslog, the kernel log buffer, the system console | |
230 | or wall. | |
231 | </para> | |
232 | ||
233 | <para>See | |
234 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
235 | for information about these settings.</para> | |
236 | </listitem> | |
237 | ||
238 | </varlistentry> | |
239 | </variablelist> | |
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240 | |
241 | <para>Note that these kernel command line options are only honoured by the default namespace, see | |
242 | above.</para> | |
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243 | </refsect1> |
244 | ||
245 | <refsect1> | |
246 | <title>Access Control</title> | |
247 | ||
248 | <para>Journal files are, by default, owned and readable by the | |
249 | <literal>systemd-journal</literal> system group but are not | |
6e866b33 | 250 | writable. Adding a user to this group thus enables them to read |
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251 | the journal files.</para> |
252 | ||
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253 | <para>By default, each user, with a UID outside the range of system users, |
254 | dynamic service users, and the nobody user, will get their own set of | |
255 | journal files in <filename>/var/log/journal/</filename>. See | |
256 | <ulink url="https://systemd.io/UIDS-GIDS">Users, Groups, UIDs and GIDs on systemd systems</ulink> | |
257 | for more details about UID ranges. These journal | |
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258 | files will not be owned by the user, however, in order to avoid |
259 | that the user can write to them directly. Instead, file system | |
260 | ACLs are used to ensure the user gets read access only.</para> | |
261 | ||
262 | <para>Additional users and groups may be granted access to journal | |
263 | files via file system access control lists (ACL). Distributions | |
264 | and administrators may choose to grant read access to all members | |
265 | of the <literal>wheel</literal> and <literal>adm</literal> system | |
266 | groups with a command such as the following:</para> | |
267 | ||
268 | <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting> | |
269 | ||
270 | <para>Note that this command will update the ACLs both for | |
271 | existing journal files and for future journal files created in the | |
272 | <filename>/var/log/journal/</filename> directory.</para> | |
273 | </refsect1> | |
274 | ||
275 | <refsect1> | |
276 | <title>Files</title> | |
277 | ||
278 | <variablelist> | |
279 | <varlistentry> | |
280 | <term><filename>/etc/systemd/journald.conf</filename></term> | |
281 | ||
b012e921 | 282 | <listitem><para>Configure <command>systemd-journald</command> behavior. See |
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283 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. |
284 | </para></listitem> | |
285 | </varlistentry> | |
286 | ||
287 | <varlistentry> | |
288 | <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term> | |
289 | <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term> | |
290 | <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term> | |
291 | <term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term> | |
292 | ||
b012e921 | 293 | <listitem><para><command>systemd-journald</command> writes entries to files in |
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294 | <filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename> |
295 | or | |
296 | <filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename> | |
297 | with the <literal>.journal</literal> suffix. If the daemon is | |
298 | stopped uncleanly, or if the files are found to be corrupted, | |
299 | they are renamed using the <literal>.journal~</literal> | |
300 | suffix, and <command>systemd-journald</command> starts writing | |
a032b68d | 301 | to a new file. <filename>/run/</filename> is used when |
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302 | <filename>/var/log/journal</filename> is not available, or |
303 | when <option>Storage=volatile</option> is set in the | |
304 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
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305 | configuration file.</para> |
306 | ||
307 | <para>When <filename>systemd-journald</filename> ceases writing to a journal file, | |
308 | it will be renamed to <literal><replaceable>original-name</replaceable>@<replaceable>suffix.journal</replaceable></literal> | |
309 | (or <literal><replaceable>original-name</replaceable>@<replaceable>suffix.journal~</replaceable></literal>). | |
310 | Such files are "archived" and will not be written to any more.</para> | |
311 | ||
312 | <para>In general, it is safe to read or copy any journal file (active or archived). | |
313 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
314 | and the functions in the | |
315 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
316 | library should be able to read all entries that have been fully written.</para> | |
317 | ||
318 | <para><filename>systemd-journald</filename> will automatically remove the oldest | |
319 | archived journal files to limit disk use. See <varname>SystemMaxUse=</varname> | |
320 | and related settings in | |
321 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. | |
322 | </para></listitem> | |
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323 | </varlistentry> |
324 | ||
325 | <varlistentry> | |
326 | <term><filename>/dev/kmsg</filename></term> | |
327 | <term><filename>/dev/log</filename></term> | |
328 | <term><filename>/run/systemd/journal/dev-log</filename></term> | |
329 | <term><filename>/run/systemd/journal/socket</filename></term> | |
330 | <term><filename>/run/systemd/journal/stdout</filename></term> | |
331 | ||
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332 | <listitem><para>Sockets and other file node paths that <command>systemd-journald</command> will |
333 | listen on and are visible in the file system. In addition to these, | |
334 | <command>systemd-journald</command> can listen for audit events using <citerefentry | |
335 | project='man-pages'><refentrytitle>netlink</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem> | |
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336 | </varlistentry> |
337 | </variablelist> | |
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338 | |
339 | <para>If journal namespacing is used these paths are slightly altered to include a namespace identifier, see above.</para> | |
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340 | </refsect1> |
341 | ||
342 | <refsect1> | |
343 | <title>See Also</title> | |
344 | <para> | |
345 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
346 | <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
347 | <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
348 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
349 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
350 | <citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>, | |
46cdbd49 | 351 | <citerefentry project='man-pages'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
6e866b33 | 352 | <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
db2df898 | 353 | <command>pydoc systemd.journal</command> |
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354 | </para> |
355 | </refsect1> | |
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356 | |
357 | </refentry> |