systemd-journald.service.xml 9.41 KB
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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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  This file is part of systemd.

  Copyright 2010 Lennart Poettering

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<refentry id="systemd-journald.service">

        <refentryinfo>
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                <title>systemd-journald.service</title>
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                <productname>systemd</productname>

                <authorgroup>
                        <author>
                                <contrib>Developer</contrib>
                                <firstname>Lennart</firstname>
                                <surname>Poettering</surname>
                                <email>lennart@poettering.net</email>
                        </author>
                </authorgroup>
        </refentryinfo>

        <refmeta>
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                <refentrytitle>systemd-journald.service</refentrytitle>
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                <manvolnum>8</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd-journald.service</refname>
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                <refname>systemd-journald.socket</refname>
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                <refname>systemd-journald</refname>
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                <refpurpose>Journal service</refpurpose>
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        </refnamediv>

        <refsynopsisdiv>
                <para><filename>systemd-journald.service</filename></para>
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                <para><filename>systemd-journald.socket</filename></para>
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                <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
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                lost at reboot. To make the data persistent it
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                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>

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        <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
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                                enabled). This must be used after
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                                <filename>/var/</filename> is mounted,
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                                as otherwise log data from
                                <filename>/run</filename> is never
                                flushed to <filename>/var</filename>
                                regardless of the
                                configuration.</para></listitem>
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                        </varlistentry>

                        <varlistentry>
                                <term>SIGUSR2</term>

                                <listitem><para>Request immediate
                                rotation of the journal
                                files.</para></listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

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        <refsect1>
                <title>Kernel Command Line</title>

                <para>A few configuration parameters from
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                <filename>journald.conf</filename> may be overridden on
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                the kernel command line:</para>

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                <variablelist class='kernel-commandline-options'>
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                        <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>
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        <refsect1>
                <title>Access Control</title>

                <para>Journal files are by default owned and readable
                by the <literal>systemd-journal</literal> system group
                (but 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>
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        <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>,
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                        <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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                        <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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                </para>
        </refsect1>

</refentry>