path: root/man/systemd.journal-fields.xml

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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, however 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 128bit message
                                        identifier ID for recognizing
                                        certain message types, if this
                                        is desirable. This should
                                        contain a 128bit id formatted
                                        as 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
                                        --new-id</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 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
                                        file name, 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><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                        formatted as 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.</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 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>_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_OWNER_UID=</varname></term>

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

                        <varlistentry>
                                <term><varname>_SELINUX_CONTEXT=</varname></term>
                                <listitem>
                                        <para>The SELinux security
                                        context 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
                                        usec since the epoch UTC
                                        formatted as 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
                                        128bit 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. One of
                                        <literal>driver</literal>,
                                        <literal>syslog</literal>,
                                        <literal>journal</literal>,
                                        <literal>stdout</literal>,
                                        <literal>kernel</literal> for
                                        internally generated messages,
                                        for those received via the
                                        local syslog socket with the
                                        syslog protocol, for those
                                        received via the native
                                        journal protocol, for the
                                        those read from a services'
                                        standard output or error
                                        output, or for those read
                                        from the kernel, respectively.
                                        </para>
                                </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>
                        <varlistentry>
                                <term>_KERNEL_DEVICE=</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 ':'
                                        and prefixed by 'b'. Similar
                                        for character devices, but
                                        prefixed by 'c'. For network
                                        devices the interface index,
                                        prefixed by 'n'. For all other
                                        devices '+' followed by the
                                        subsystem name, followed by
                                        ':', followed by the kernel
                                        device name.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term>_KERNEL_SUBSYSTEM=</term>
                                <listitem>
                                        <para>The kernel subsystem name.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term>_UDEV_SYSNAME=</term>
                                <listitem>
                                        <para>The kernel device name
                                        as it shows up in the device
                                        tree below
                                        <filename>/sys</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term>_UDEV_DEVNODE=</term>
                                <listitem>
                                        <para>The device node path of
                                        this device in
                                        <filename>/dev</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term>_UDEV_DEVLINK=</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>Address Fields</title>

                <para>During serialization into external formats the
                addresses of journal entries are serialized into
                fields prefixed with double underscores. Note that
                these aren't proper fields when stored in the journal,
                but addressing meta data 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
                                        (CLOCK_REALTIME) at the point
                                        in time the entry was received
                                        by the journal, in usec since
                                        the epoch UTC formatted as
                                        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
                                        (CLOCK_MONOTONIC) at the point
                                        in time the entry was received
                                        by the journal in usec
                                        formatted as decimal
                                        string. To be useful as an
                                        address for the entry this
                                        should be combined with with
                                        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>
                  </para>
        </refsect1>

</refentry>