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-audit.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>/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>

    <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>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. The
        <command>journalctl --flush</command> command uses this signal
        to request flushing of the journal files, and then waits 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. The <command>journalctl --rotate</command> command uses
        this signal to request journal file
        rotation.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term>SIGRTMIN+1</term>

        <listitem><para>Request that all unwritten log data is written
        to disk. The <command>journalctl --sync</command> command uses
        this signal to trigger journal synchronization, and then waits
        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>
  </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>
        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></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 paths that
        <command>systemd-journald</command> will listen on that are
        visible in the file system. In addition to these, journald can
        listen for audit events using netlink.</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 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>
    </para>
  </refsect1>

</refentry>