1<?xml version='1.0'?> <!--*-nxml-*--> 2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" 3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> 4<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> 5 6<refentry id="systemd-journald.service"> 7 8 <refentryinfo> 9 <title>systemd-journald.service</title> 10 <productname>systemd</productname> 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> 22 <refname>systemd-journald-audit.socket</refname> 23 <refname>systemd-journald@.service</refname> 24 <refname>systemd-journald@.socket</refname> 25 <refname>systemd-journald-varlink@.socket</refname> 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> 34 <para><filename>systemd-journald-audit.socket</filename></para> 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> 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 52 <listitem><para>Simple system log messages, via the <filename>libc</filename> <citerefentry 53 project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> 54 call</para></listitem> 55 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> 60 61 <listitem><para>Standard output and standard error of service units. For further details see 62 below.</para></listitem> 63 64 <listitem><para>Audit records, originating from the kernel audit subsystem</para></listitem> 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 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 2⁶⁴-1 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> 82 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 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> 91 92 <programlisting>mkdir -p /var/log/journal 93systemd-tmpfiles --create --prefix /var/log/journal</programlisting> 94 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> 99 100 <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 113 ignore such errors. If the <constant>SIGPIPE</constant> UNIX signal handler is not blocked or turned off, such 114 write attempts will also result in such process signals being generated, see 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 119 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for 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> 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> 135 136 <para>In addition to the implicit standard output/error logging of services, stream logging is also available 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 141 4096. When this limit is reached further log streams may be established but will receive 142 <constant>EPIPE</constant> right from the beginning.</para> 143 </refsect1> 144 145 <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> 178 179 <refsect1> 180 <title>Signals</title> 181 182 <variablelist> 183 <varlistentry> 184 <term>SIGUSR1</term> 185 186 <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 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 190 <command>journalctl --flush</command> command to request flushing of the journal files, and wait for 191 the operation to complete. See 192 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for 193 details.</para></listitem> 194 </varlistentry> 195 196 <varlistentry> 197 <term>SIGUSR2</term> 198 199 <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> 202 </varlistentry> 203 204 <varlistentry> 205 <term>SIGRTMIN+1</term> 206 207 <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> 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> 240 241 <para>Note that these kernel command line options are only honoured by the default namespace, see 242 above.</para> 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 250 writable. Adding a user to this group thus enables them to read 251 the journal files.</para> 252 253 <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 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> 281 282 <listitem><para>Configure <command>systemd-journald</command> behavior. See 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> 292 293 <listitem><para><command>systemd-journald</command> writes entries to files in 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 301 to a new file. <filename>/run/</filename> is used when 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> 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> 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> 331 332 <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> 336 </varlistentry> 337 </variablelist> 338 339 <para>If journal namespacing is used these paths are slightly altered to include a namespace identifier, see above.</para> 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>, 351 <citerefentry project='man-pages'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, 352 <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 353 <command>pydoc systemd.journal</command> 354 </para> 355 </refsect1> 356 357</refentry> 358