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<refentry id="systemd.journal-fields">

        <refentryinfo>
                <title>systemd.journal-fields</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.journal-fields</refentrytitle>
                <manvolnum>7</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd.journal-fields</refname>
                <refpurpose>Special journal fields</refpurpose>
        </refnamediv>

        <refsect1>
                <title>Description</title>

                <para>Entries in the journal resemble an environment
                block in their syntax but with fields that can
                include binary data. Primarily, fields are formatted
                UTF-8 text strings, and binary formatting is used only
                where formatting as UTF-8 text strings makes little
                sense. New fields may freely be defined by
                applications, but a few fields have special
                meaning. All fields with special meanings are
                optional. In some cases, fields may appear more than
                once per entry.</para>
        </refsect1>

        <refsect1>
                <title>User Journal Fields</title>

                <para>User fields are fields that are directly passed
                from clients and stored in the journal.</para>

                <variablelist class='journal-directives'>
                        <varlistentry>
                                <term><varname>MESSAGE=</varname></term>
                                <listitem>
                                        <para>The human-readable
                                        message string for this
                                        entry. This is supposed to be
                                        the primary text shown to the
                                        user. It is usually not
                                        translated (but might be in
                                        some cases), and is not
                                        supposed to be parsed for meta
                                        data.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>MESSAGE_ID=</varname></term>
                                <listitem>
                                        <para>A 128-bit message
                                        identifier ID for recognizing
                                        certain message types, if this
                                        is desirable. This should
                                        contain a 128-bit ID formatted
                                        as a lower-case hexadecimal
                                        string, without any separating
                                        dashes or suchlike. This is
                                        recommended to be a
                                        UUID-compatible ID, but this is not
                                        enforced, and formatted
                                        differently. Developers can
                                        generate a new ID for this
                                        purpose with <command>journalctl
                                        <option>--new-id</option></command>.
                                        </para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>PRIORITY=</varname></term>
                                <listitem>
                                        <para>A priority value between
                                        0 (<literal>emerg</literal>)
                                        and 7
                                        (<literal>debug</literal>)
                                        formatted as a decimal
                                        string. This field is
                                        compatible with syslog's
                                        priority concept.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>CODE_FILE=</varname></term>
                                <term><varname>CODE_LINE=</varname></term>
                                <term><varname>CODE_FUNC=</varname></term>
                                <listitem>
                                        <para>The code location
                                        generating this message, if
                                        known. Contains the source
                                        filename, the line number and
                                        the function name.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>ERRNO=</varname></term>
                                <listitem>
                                        <para>The low-level Unix error
                                        number causing this entry, if
                                        any. Contains the numeric
                                        value of
                                        <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                        formatted as a decimal
                                        string.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>SYSLOG_FACILITY=</varname></term>
                                <term><varname>SYSLOG_IDENTIFIER=</varname></term>
                                <term><varname>SYSLOG_PID=</varname></term>
                                <listitem>
                                        <para>Syslog compatibility
                                        fields containing the facility
                                        (formatted as decimal string),
                                        the identifier string
                                        (i.e. "tag"), and the client
                                        PID. (Note that the tag is
                                        usually derived from glibc's
                                        <varname>program_invocation_short_name</varname>
                                        variable, see <citerefentry><refentrytitle>program_invocation_short_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>.)</para>
                                </listitem>

                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Trusted Journal Fields</title>

                <para>Fields prefixed with an underscore are trusted
                fields, i.e. fields that are implicitly added by the
                journal and cannot be altered by client code.</para>

                <variablelist class='journal-directives'>
                        <varlistentry>
                                <term><varname>_PID=</varname></term>
                                <term><varname>_UID=</varname></term>
                                <term><varname>_GID=</varname></term>
                                <listitem>
                                        <para>The process, user, and
                                        group ID of the process the
                                        journal entry originates from
                                        formatted as a decimal
                                        string.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_COMM=</varname></term>
                                <term><varname>_EXE=</varname></term>
                                <term><varname>_CMDLINE=</varname></term>
                                <listitem>
                                        <para>The name, the executable
                                        path, and the command line of
                                        the process the journal entry
                                        originates from.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_CAP_EFFECTIVE=</varname></term>
                                <listitem>
                                        <para>The effective <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry> of
                                        the process the journal entry
                                        originates from.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_AUDIT_SESSION=</varname></term>
                                <term><varname>_AUDIT_LOGINUID=</varname></term>
                                <listitem>
                                        <para>The session and login
                                        UID of the process the journal
                                        entry originates from, as
                                        maintained by the kernel audit
                                        subsystem.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_SYSTEMD_CGROUP=</varname></term>
                                <term><varname>_SYSTEMD_SESSION=</varname></term>
                                <term><varname>_SYSTEMD_UNIT=</varname></term>
                                <term><varname>_SYSTEMD_USER_UNIT=</varname></term>
                                <term><varname>_SYSTEMD_OWNER_UID=</varname></term>
                                <term><varname>_SYSTEMD_SLICE=</varname></term>

                                <listitem>
                                        <para>The control group path
                                        in the systemd hierarchy, the
                                        systemd session ID (if any),
                                        the systemd unit name (if
                                        any), the systemd user session
                                        unit name (if any), the owner
                                        UID of the systemd session (if
                                        any) and the systemd slice
                                        unit of the process the
                                        journal entry originates
                                        from.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_SELINUX_CONTEXT=</varname></term>
                                <listitem>
                                        <para>The SELinux security
                                        context (label) of the process
                                        the journal entry originates
                                        from.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_SOURCE_REALTIME_TIMESTAMP=</varname></term>
                                <listitem>
                                        <para>The earliest trusted
                                        timestamp of the message, if
                                        any is known that is different
                                        from the reception time of the
                                        journal. This is the time in
                                        microseconds since the epoch UTC,
                                        formatted as a decimal
                                        string.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_BOOT_ID=</varname></term>
                                <listitem>
                                        <para>The kernel boot ID for
                                        the boot the message was
                                        generated in, formatted as
                                        a 128-bit hexadecimal
                                        string.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_MACHINE_ID=</varname></term>
                                <listitem>
                                        <para>The machine ID of the
                                        originating host, as available
                                        in
                                        <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_HOSTNAME=</varname></term>
                                <listitem>
                                        <para>The name of the
                                        originating host.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_TRANSPORT=</varname></term>
                                <listitem>
                                        <para>How the entry was
                                        received by the journal
                                        service. Valid transports are:
                                        </para>
                                        <variablelist>
                                                <varlistentry>
                                                        <term>
                                                                <option>driver</option>
                                                        </term>
                                                        <listitem>
                                                                <para>for
                                                                internally
                                                                generated
                                                                messages
                                                                </para>
                                                        </listitem>
                                                </varlistentry>

                                                <varlistentry>
                                                        <term>
                                                                <option>syslog</option>
                                                        </term>
                                                        <listitem>
                                                                <para>for those
                                                                received via the
                                                                local syslog
                                                                socket with the
                                                                syslog protocol
                                                                </para>
                                                        </listitem>
                                                </varlistentry>

                                                <varlistentry>
                                                        <term>
                                                                <option>journal</option>
                                                        </term>
                                                        <listitem>
                                                                <para>for those
                                                                received via the
                                                                native journal
                                                                protocol
                                                                </para>
                                                        </listitem>
                                                </varlistentry>

                                                <varlistentry>
                                                        <term>
                                                                <option>stdout</option>
                                                        </term>
                                                        <listitem>
                                                                <para>for those
                                                                read from a
                                                                service's
                                                                standard output
                                                                or error output
                                                                </para>
                                                        </listitem>
                                                </varlistentry>

                                                <varlistentry>
                                                        <term>
                                                                <option>kernel</option>
                                                        </term>
                                                        <listitem>
                                                                <para>for those
                                                                read from the
                                                                kernel
                                                                </para>
                                                        </listitem>
                                                </varlistentry>
                                        </variablelist>
                                </listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Kernel Journal Fields</title>

                <para>Kernel fields are fields that are used by
                messages originating in the kernel and stored in the
                journal.</para>

                <variablelist class='journal-directives'>
                        <varlistentry>
                                <term><varname>_KERNEL_DEVICE=</varname></term>
                                <listitem>
                                        <para>The kernel device
                                        name. If the entry is
                                        associated to a block device,
                                        the major and minor of the
                                        device node, separated by <literal>:</literal>
                                        and prefixed by <literal>b</literal>. Similar
                                        for character devices but
                                        prefixed by <literal>c</literal>. For network
                                        devices, this is the interface index
                                        prefixed by <literal>n</literal>. For all other
                                        devices, this is the subsystem name
                                        prefixed by <literal>+</literal>, followed by
                                        <literal>:</literal>, followed by the kernel
                                        device name.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><varname>_KERNEL_SUBSYSTEM=</varname></term>
                                <listitem>
                                        <para>The kernel subsystem name.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><varname>_UDEV_SYSNAME=</varname></term>
                                <listitem>
                                        <para>The kernel device name
                                        as it shows up in the device
                                        tree below
                                        <filename>/sys</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><varname>_UDEV_DEVNODE=</varname></term>
                                <listitem>
                                        <para>The device node path of
                                        this device in
                                        <filename>/dev</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><varname>_UDEV_DEVLINK=</varname></term>
                                <listitem>
                                        <para>Additional symlink names
                                        pointing to the device node in
                                        <filename>/dev</filename>. This
                                        field is frequently set more
                                        than once per entry.</para>
                                </listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Fields to log on behalf of a different program</title>

                <para>Fields in this section are used by programs
                to specify that they are logging on behalf of another
                program or unit.
                </para>

                <para>Fields used by the <command>systemd-coredump</command>
                coredump kernel helper:
                </para>

                <variablelist class='journal-directives'>
                        <varlistentry>
                                <term><varname>COREDUMP_UNIT=</varname></term>
                                <term><varname>COREDUMP_USER_UNIT=</varname></term>
                                <listitem>
                                        <para>Used to annotate
                                        messages containing coredumps from
                                        system and session units.
                                        See
                                        <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
                                        </para>
                                </listitem>
                        </varlistentry>
                </variablelist>

                <para>Priviledged programs (currently UID 0) may
                attach <varname>OBJECT_PID=</varname> to a
                message. This will instruct
                <command>systemd-journald</command> to attach
                additional fields on behalf of the caller:</para>

                <variablelist class='journal-directives'>
                        <varlistentry>
                                <term><varname>OBJECT_PID=<replaceable>PID</replaceable></varname></term>
                                <listitem>
                                        <para>PID of the program that this
                                        message pertains to.
                                        </para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>OBJECT_UID=</varname></term>
                                <term><varname>OBJECT_GID=</varname></term>
                                <term><varname>OBJECT_COMM=</varname></term>
                                <term><varname>OBJECT_EXE=</varname></term>
                                <term><varname>OBJECT_CMDLINE=</varname></term>
                                <term><varname>OBJECT_AUDIT_SESSION=</varname></term>
                                <term><varname>OBJECT_AUDIT_LOGINUID=</varname></term>
                                <term><varname>OBJECT_SYSTEMD_CGROUP=</varname></term>
                                <term><varname>OBJECT_SYSTEMD_SESSION=</varname></term>
                                <term><varname>OBJECT_SYSTEMD_OWNER_UID=</varname></term>
                                <term><varname>OBJECT_SYSTEMD_UNIT=</varname></term>
                                <term><varname>OBJECT_SYSTEMD_USER_UNIT=</varname></term>
                                <listitem>
                                        <para>These are additional fields added automatically
                                        by <command>systemd-journald</command>.
                                        Their meaning is the same as
                                        <varname>_UID=</varname>,
                                        <varname>_GID=</varname>,
                                        <varname>_COMM=</varname>,
                                        <varname>_EXE=</varname>,
                                        <varname>_CMDLINE=</varname>,
                                        <varname>_AUDIT_SESSION=</varname>,
                                        <varname>_AUDIT_LOGINUID=</varname>,
                                        <varname>_SYSTEMD_CGROUP=</varname>,
                                        <varname>_SYSTEMD_SESSION=</varname>,
                                        <varname>_SYSTEMD_UNIT=</varname>,
                                        <varname>_SYSTEMD_USER_UNIT=</varname>, and
                                        <varname>_SYSTEMD_OWNER_UID=</varname>
                                        as described above, except that the
                                        process identified by <replaceable>PID</replaceable>
                                        is described, instead of the process
                                        which logged the message.</para>
                                </listitem>
                        </varlistentry>
                </variablelist>


        </refsect1>

        <refsect1>
                <title>Address Fields</title>

                <para>During serialization into external formats, such
                as the <ulink
                url="http://www.freedesktop.org/wiki/Software/systemd/export">Journal
                Export Format</ulink> or the <ulink
                url="http://www.freedesktop.org/wiki/Software/systemd/json">Journal
                JSON Format</ulink>, the addresses of journal entries
                are serialized into fields prefixed with double
                underscores. Note that these are not proper fields when
                stored in the journal but for addressing metadata of
                entries. They cannot be written as part of structured
                log entries via calls such as
                <citerefentry><refentrytitle>sd_journal_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>. They
                may also not be used as matches for
                <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry></para>

                <variablelist class='journal-directives'>
                        <varlistentry>
                                <term><varname>__CURSOR=</varname></term>
                                <listitem>
                                        <para>The cursor for the
                                        entry. A cursor is an opaque
                                        text string that uniquely
                                        describes the position of an
                                        entry in the journal and is
                                        portable across machines,
                                        platforms and journal files.
                                        </para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>__REALTIME_TIMESTAMP=</varname></term>
                                <listitem>
                                        <para>The wallclock time
                                        (<constant>CLOCK_REALTIME</constant>)
                                        at the point in time the entry
                                        was received by the journal,
                                        in microseconds since the epoch
                                        UTC, formatted as a decimal
                                        string. This has different
                                        properties from
                                        <literal>_SOURCE_REALTIME_TIMESTAMP=</literal>,
                                        as it is usually a bit later
                                        but more likely to be monotonic.
                                        </para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>__MONOTONIC_TIMESTAMP=</varname></term>
                                <listitem>
                                        <para>The monotonic time
                                        (<constant>CLOCK_MONOTONIC</constant>)
                                        at the point in time the entry
                                        was received by the journal in
                                        microseconds, formatted as a decimal
                                        string. To be useful as an
                                        address for the entry, this
                                        should be combined with the
                                        boot ID in <literal>_BOOT_ID=</literal>.
                                        </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>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                  </para>
        </refsect1>

</refentry>
