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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 15:35:18 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 15:35:18 +0000
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Adding upstream version 252.22.upstream/252.22
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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="systemd-journald.service">
+
+ <refentryinfo>
+ <title>systemd-journald.service</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>systemd-journald.service</refentrytitle>
+ <manvolnum>8</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>systemd-journald.service</refname>
+ <refname>systemd-journald.socket</refname>
+ <refname>systemd-journald-dev-log.socket</refname>
+ <refname>systemd-journald-audit.socket</refname>
+ <refname>systemd-journald@.service</refname>
+ <refname>systemd-journald@.socket</refname>
+ <refname>systemd-journald-varlink@.socket</refname>
+ <refname>systemd-journald</refname>
+ <refpurpose>Journal service</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <para><filename>systemd-journald.service</filename></para>
+ <para><filename>systemd-journald.socket</filename></para>
+ <para><filename>systemd-journald-dev-log.socket</filename></para>
+ <para><filename>systemd-journald-audit.socket</filename></para>
+ <para><filename>systemd-journald@.service</filename></para>
+ <para><filename>systemd-journald@.socket</filename></para>
+ <para><filename>systemd-journald-varlink@.socket</filename></para>
+ <para><filename>/usr/lib/systemd/systemd-journald</filename></para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><filename>systemd-journald</filename> is a system service
+ that collects and stores logging data. It creates and maintains
+ structured, indexed journals based on logging information that is
+ received from a variety of sources:</para>
+
+ <itemizedlist>
+ <listitem><para>Kernel log messages, via kmsg</para></listitem>
+
+ <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>3</manvolnum></citerefentry>
+ and <ulink url="https://systemd.io/JOURNAL_NATIVE_PROTOCOL">Native Journal
+ Protocol</ulink></para></listitem>
+
+ <listitem><para>Standard output and standard error of service units. For further details see
+ below.</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 each log messages in a secure and unfakeable way. See
+ <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ 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. Individual fields making up a log record stored in the journal may be up to 2⁶⁴-1 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>Note that journald will initially use volatile storage, until a call to
+ <command>journalctl --flush</command> (or sending <constant>SIGUSR1</constant> to journald) will cause
+ it to switch to persistent logging (under the conditions mentioned above). This is done automatically
+ on boot via <literal>systemd-journal-flush.service</literal>.</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>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 project='man-pages'><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>Journal Namespaces</title>
+
+ <para>Journal 'namespaces' are both a mechanism for logically isolating the log stream of projects
+ consisting of one or more services from the rest of the system and a mechanism for improving
+ performance. Multiple journal namespaces may exist simultaneously, each defining its own, independent log
+ stream managed by its own instance of <command>systemd-journald</command>. Namespaces are independent of
+ each other, both in the data store and in the IPC interface. By default only a single 'default' namespace
+ exists, managed by <filename>systemd-journald.service</filename> (and its associated socket
+ units). Additional namespaces are created by starting an instance of the
+ <filename>systemd-journald@.service</filename> service template. The instance name is the namespace
+ identifier, which is a short string used for referencing the journal namespace. Service units may be
+ assigned to a specific journal namespace through the <varname>LogNamespace=</varname> unit file setting,
+ see <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
+ details. The <option>--namespace=</option> switch of
+ <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> may be
+ used to view the log stream of a specific namespace. If the switch is not used the log stream of the
+ default namespace is shown, i.e. log data from other namespaces is not visible.</para>
+
+ <para>Services associated with a specific log namespace may log via syslog, the native logging protocol
+ of the journal and via stdout/stderr; the logging from all three transports is associated with the
+ namespace.</para>
+
+ <para>By default only the default namespace will collect kernel and audit log messages.</para>
+
+ <para>The <command>systemd-journald</command> instance of the default namespace is configured through
+ <filename>/etc/systemd/journald.conf</filename> (see below), while the other instances are configured
+ through <filename>/etc/systemd/journald@<replaceable>NAMESPACE</replaceable>.conf</filename>. The journal
+ log data for the default namespace is placed in
+ <filename>/var/log/journal/<replaceable>MACHINE_ID</replaceable></filename> (see below) while the data
+ for the other namespaces is located in
+ <filename>/var/log/journal/<replaceable>MACHINE_ID</replaceable>.<replaceable>NAMESPACE</replaceable></filename>.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Signals</title>
+
+ <variablelist>
+ <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. 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. 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>
+
+ <refsect1>
+ <title>Kernel Command Line</title>
+
+ <para>A few configuration parameters from
+ <filename>journald.conf</filename> may be overridden on the kernel
+ command line:</para>
+
+ <variablelist class='kernel-commandline-options'>
+ <varlistentry>
+ <term><varname>systemd.journald.forward_to_syslog=</varname></term>
+ <term><varname>systemd.journald.forward_to_kmsg=</varname></term>
+ <term><varname>systemd.journald.forward_to_console=</varname></term>
+ <term><varname>systemd.journald.forward_to_wall=</varname></term>
+
+ <listitem><para>Enables/disables forwarding of collected log
+ messages to syslog, the kernel log buffer, the system console
+ or wall.
+ </para>
+
+ <para>See
+ <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for information about these settings.</para>
+ </listitem>
+
+ </varlistentry>
+ </variablelist>
+
+ <para>Note that these kernel command line options are only honoured by the default namespace, see
+ above.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Access Control</title>
+
+ <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 them to read
+ the journal files.</para>
+
+ <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>
+
+ <para>Additional users and groups may be granted access to journal
+ files via file system access control lists (ACL). Distributions
+ and administrators may choose to grant read access to all members
+ of the <literal>wheel</literal> and <literal>adm</literal> system
+ groups with a command such as the following:</para>
+
+ <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>
+
+ <para>Note that this command will update the ACLs both for
+ existing journal files and for future journal files created in the
+ <filename>/var/log/journal/</filename> directory.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Files</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>/etc/systemd/journald.conf</filename></term>
+
+ <listitem><para>Configure <command>systemd-journald</command> behavior. See
+ <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal</filename></term>
+ <term><filename>/run/log/journal/<replaceable>machine-id</replaceable>/*.journal~</filename></term>
+ <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
+ <filename>/run/log/journal/<replaceable>machine-id</replaceable>/</filename>
+ or
+ <filename>/var/log/journal/<replaceable>machine-id</replaceable>/</filename>
+ with the <literal>.journal</literal> suffix. If the daemon is
+ stopped uncleanly, or if the files are found to be corrupted,
+ they are renamed using the <literal>.journal~</literal>
+ suffix, and <command>systemd-journald</command> starts writing
+ to a new file. <filename>/run/</filename> is used when
+ <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>
+
+ <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>
+ <term><filename>/dev/kmsg</filename></term>
+ <term><filename>/dev/log</filename></term>
+ <term><filename>/run/systemd/journal/dev-log</filename></term>
+ <term><filename>/run/systemd/journal/socket</filename></term>
+ <term><filename>/run/systemd/journal/stdout</filename></term>
+
+ <listitem><para>Sockets and other file node paths that <command>systemd-journald</command> will
+ listen on and are visible in the file system. In addition to these,
+ <command>systemd-journald</command> can listen for audit events using <citerefentry
+ project='man-pages'><refentrytitle>netlink</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>If journal namespacing is used these paths are slightly altered to include a namespace identifier, see above.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry project='man-pages'><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <command>pydoc systemd.journal</command>
+ </para>
+ </refsect1>
+
+</refentry>