systemd/man/systemd-journald.service.xml

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<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>
                <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</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>/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
                        libc <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>

                        <listitem><para>Standard output and
                        standard error of system
                        services</para></listitem>

                        <listitem><para>Audit records, via the 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. All objects stored in the journal can be up
                to 2^64-1 bytes in size.</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><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>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.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGUSR2</term>

                                <listitem><para>Request immediate
                                rotation of the journal
                                files.</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>
        </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 her/him 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 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>
                                behaviour. 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></listitem>
                        </varlistentry>
                </variablelist>
        </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><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
                        <command>pydoc systemd.journal</command>.
                </para>
        </refsect1>

</refentry>