<?xml version='1.0'?> <!--*-nxml-*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
-
-<!--
- This file is part of systemd.
-
- Copyright 2010 Lennart Poettering
-
- systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 2.1 of the License, or
- (at your option) any later version.
-
- systemd is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with systemd; If not, see <http://www.gnu.org/licenses/>.
--->
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="systemd-journald.service">
<refentryinfo>
<title>systemd-journald.service</title>
<productname>systemd</productname>
-
- <authorgroup>
- <author>
- <contrib>Developer</contrib>
- <firstname>Lennart</firstname>
- <surname>Poettering</surname>
- <email>lennart@poettering.net</email>
- </author>
- </authorgroup>
</refentryinfo>
<refmeta>
<itemizedlist>
<listitem><para>Kernel log messages, via kmsg</para></listitem>
- <listitem><para>Simple system log messages, via the libc
- <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ <listitem><para>Simple system log messages, via the <filename>libc</filename> <citerefentry
+ project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
call</para></listitem>
<listitem><para>Structured system log messages via the native
Journal API, see
- <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry></para></listitem>
+ <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry></para></listitem>
- <listitem><para>Standard output and standard error of system
- services</para></listitem>
+ <listitem><para>Standard output and standard error of service units. For further details see
+ below.</para></listitem>
- <listitem><para>Audit records, via the audit
- subsystem</para></listitem>
+ <listitem><para>Audit records, originating from the kernel audit subsystem</para></listitem>
</itemizedlist>
<para>The daemon will implicitly collect numerous metadata fields
for more information about the collected metadata.
</para>
- <para>Log data collected by the journal is primarily text-based
- but can also include binary data where necessary. All objects
- stored in the journal can be up to 2^64-1 bytes in size.</para>
+ <para>Log data collected by the journal is primarily text-based but can also include binary data where
+ necessary. Individual fields making up a log record stored in the journal may be up to 2^64-1 bytes in size.</para>
+
+ <para>The journal service stores log data either persistently below <filename>/var/log/journal</filename> or in a
+ volatile way below <filename>/run/log/journal/</filename> (in the latter case it is lost at reboot). By default, log
+ data is stored persistently if <filename>/var/log/journal/</filename> exists during boot, with an implicit fallback
+ to volatile storage otherwise. Use <varname>Storage=</varname> in
+ <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> to configure
+ where log data is placed, independently of the existence of <filename>/var/log/journal/</filename>.</para>
- <para>By default, the journal stores log data in
- <filename>/run/log/journal/</filename>. Since
- <filename>/run/</filename> is volatile, log data is lost at
- reboot. To make the data persistent, it is sufficient to create
- <filename>/var/log/journal/</filename> where
- <filename>systemd-journald</filename> will then store the
- data:</para>
+ <para>On systems where <filename>/var/log/journal/</filename> does not exist yet but where persistent logging is
+ desired (and the default <filename>journald.conf</filename> is used), it is sufficient to create the directory, and
+ ensure it has the correct access modes and ownership:</para>
<programlisting>mkdir -p /var/log/journal
systemd-tmpfiles --create --prefix /var/log/journal</programlisting>
- <para><filename>systemd-journald</filename> will forward all
- received log messages to the
- <constant>AF_UNIX</constant>/<constant>SOCK_DGRAM</constant>
- socket <filename>/run/systemd/journal/syslog</filename>, if it
- exists, which may be used by Unix syslog daemons to process the
- data further.</para>
-
<para>See
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for information about the configuration of this service.</para>
</refsect1>
+ <refsect1>
+ <title>Stream logging</title>
+
+ <para>The systemd service manager invokes all service processes with standard output and standard error connected
+ to the journal by default. This behaviour may be altered via the
+ <varname>StandardOutput=</varname>/<varname>StandardError=</varname> unit file settings, see
+ <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The
+ journal converts the log byte stream received this way into individual log records, splitting the stream at newline
+ (<literal>\n</literal>, ASCII <constant>10</constant>) and <constant>NUL</constant> bytes.</para>
+
+ <para>If <filename>systemd-journald.service</filename> is stopped, the stream connections associated with all
+ services are terminated. Further writes to those streams by the service will result in <constant>EPIPE</constant>
+ errors. In order to react gracefully in this case it is recommended that programs logging to standard output/error
+ ignore such errors. If the <constant>SIGPIPE</constant> UNIX signal handler is not blocked or turned off, such
+ write attempts will also result in such process signals being generated, see
+ <citerefentry><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>. To mitigate this issue,
+ systemd service manager explicitly turns off the <constant>SIGPIPE</constant> signal for all invoked processes by
+ default (this may be changed for each unit individually via the <varname>IgnoreSIGPIPE=</varname> option, see
+ <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
+ details). After the standard output/standard error streams have been terminated they may not be recovered until the
+ services they are associated with are restarted. Note that during normal operation,
+ <filename>systemd-journald.service</filename> stores copies of the file descriptors for those streams in the
+ service manager. If <filename>systemd-journald.service</filename> is restarted using <command>systemctl
+ restart</command> or equivalent operation instead of a pair of separate <command>systemctl stop</command> and
+ <command>systemctl start</command> commands (or equivalent operations), these stream connections are not terminated
+ and survive the restart. It is thus safe to restart <filename>systemd-journald.service</filename>, but stopping it
+ is not recommended.</para>
+
+ <para>Note that the log record metadata for records transferred via such standard output/error streams reflect the
+ metadata of the peer the stream was originally created for. If the stream connection is passed on to other
+ processes (such as further child processes forked off the main service process), the log records will not reflect
+ their metadata, but will continue to describe the original process. This is different from the other logging
+ transports listed above, which are inherently record based and where the metadata is always associated with the
+ individual record.</para>
+
+ <para>In addition to the implicit standard output/error logging of services, stream logging is also available
+ via the <citerefentry><refentrytitle>systemd-cat</refentrytitle><manvolnum>1</manvolnum></citerefentry> command
+ line tool.</para>
+
+ <para>Currently, the number of parallel log streams <filename>systemd-journald</filename> will accept is limited to
+ 4096. When this limit is reached further log streams may be established but will receive
+ <constant>EPIPE</constant> right from the beginning.</para>
+ </refsect1>
+
<refsect1>
<title>Signals</title>
<varlistentry>
<term>SIGUSR1</term>
- <listitem><para>Request that journal data from
- <filename>/run/</filename> is flushed to
- <filename>/var/</filename> in order to make it persistent (if
- this is enabled). This must be used after
- <filename>/var/</filename> is mounted, as otherwise log data
- from <filename>/run</filename> is never flushed to
- <filename>/var</filename> regardless of the
- configuration.</para></listitem>
+ <listitem><para>Request that journal data from <filename>/run/</filename> is flushed to
+ <filename>/var/</filename> in order to make it persistent (if this is enabled). This must be used
+ after <filename>/var/</filename> is mounted, as otherwise log data from <filename>/run</filename> is
+ never flushed to <filename>/var</filename> regardless of the configuration. Use the
+ <command>journalctl --flush</command> command to request flushing of the journal files, and wait for
+ the operation to complete. See
+ <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
+ details.</para></listitem>
</varlistentry>
<varlistentry>
<term>SIGUSR2</term>
- <listitem><para>Request immediate rotation of the journal
- files.</para></listitem>
+ <listitem><para>Request immediate rotation of the journal files. Use the <command>journalctl
+ --rotate</command> command to request journal file rotation, and wait for the operation to
+ complete.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>SIGRTMIN+1</term>
+
+ <listitem><para>Request that all unwritten log data is written to disk. Use the <command>journalctl
+ --sync</command> command to trigger journal synchronization, and wait for the operation to
+ complete.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<para>Journal files are, by default, owned and readable by the
<literal>systemd-journal</literal> system group but are not
- writable. Adding a user to this group thus enables her/him to read
+ writable. Adding a user to this group thus enables them to read
the journal files.</para>
- <para>By default, each logged in user will get her/his own set of
- journal files in <filename>/var/log/journal/</filename>. These
+ <para>By default, each user, with a UID outside the range of system users,
+ dynamic service users, and the nobody user, will get their own set of
+ journal files in <filename>/var/log/journal/</filename>. See
+ <ulink url="https://systemd.io/UIDS-GIDS">Users, Groups, UIDs and GIDs on systemd systems</ulink>
+ for more details about UID ranges. These journal
files will not be owned by the user, however, in order to avoid
that the user can write to them directly. Instead, file system
ACLs are used to ensure the user gets read access only.</para>
<varlistentry>
<term><filename>/etc/systemd/journald.conf</filename></term>
- <listitem><para>Configure
- <command>systemd-journald</command>
- behavior. See
+ <listitem><para>Configure <command>systemd-journald</command> behavior. See
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
<term><filename>/var/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
- <listitem><para><command>systemd-journald</command> writes
- entries to files in
+ <listitem><para><command>systemd-journald</command> writes entries to files in
<filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename>
or
<filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename>
<filename>/var/log/journal</filename> is not available, or
when <option>Storage=volatile</option> is set in the
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
- configuration file.</para></listitem>
+ configuration file.</para>
+
+ <para>When <filename>systemd-journald</filename> ceases writing to a journal file,
+ it will be renamed to <literal><replaceable>original-name</replaceable>@<replaceable>suffix.journal</replaceable></literal>
+ (or <literal><replaceable>original-name</replaceable>@<replaceable>suffix.journal~</replaceable></literal>).
+ Such files are "archived" and will not be written to any more.</para>
+
+ <para>In general, it is safe to read or copy any journal file (active or archived).
+ <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ and the functions in the
+ <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ library should be able to read all entries that have been fully written.</para>
+
+ <para><filename>systemd-journald</filename> will automatically remove the oldest
+ archived journal files to limit disk use. See <varname>SystemMaxUse=</varname>
+ and related settings in
+ <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+ </para></listitem>
</varlistentry>
<varlistentry>
<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
- <command>pydoc systemd.journal</command>.
+ <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <command>pydoc systemd.journal</command>
</para>
</refsect1>
projects / thirdparty / systemd.git / blobdiff