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</refname>
                <refpurpose>systemd Journal Service</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <para><filename>systemd-journald.service</filename></para>
                <para><filename>systemd-journald.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 the kernel, from user processes via the libc
                <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                call, from STDOUT/STDERR of system services or via its
                native API. It will implicitly collect numerous meta
                data 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 meta data.
                </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 AF_UNIX
                SOCK_DGRAM 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 may be used after
                                <filename>/var/</filename> is mounted,
                                but is generally not required since
                                the first journal write when
                                <filename>/var/</filename> becomes
                                writable triggers the flushing
                                anyway.</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 overriden on
                the kernel command line:</para>

                <variablelist>
                        <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>

                                <listitem><para>Enables/disables
                                forwarding of collected log messages
                                to syslog, the kernel log buffer or
                                the system console.
                                </para>

                                <para>See
                                <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                for information about these settings.</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>
                </para>
        </refsect1>

</refentry>