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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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<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
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                block in their syntax but with fields that can
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                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
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                optional. In some cases, fields may appear more than
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                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>
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                                        <para>The human-readable
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                                        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>
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                                        <para>A 128-bit message
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                                        identifier ID for recognizing
                                        certain message types, if this
                                        is desirable. This should
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                                        contain a 128-bit ID formatted
                                        as a lower-case hexadecimal
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                                        string, without any separating
                                        dashes or suchlike. This is
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                                        recommended to be a
                                        UUID-compatible ID, but this is not
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                                        enforced, and formatted
                                        differently. Developers can
                                        generate a new ID for this
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                                        purpose with <command>journalctl
                                        <option>--new-id</option></command>.
                                        </para>
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                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>PRIORITY=</varname></term>
                                <listitem>
                                        <para>A priority value between
                                        0 (<literal>emerg</literal>)
                                        and 7
                                        (<literal>debug</literal>)
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                                        formatted as a decimal
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                                        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
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                                        filename, the line number and
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                                        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>
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                                        formatted as a decimal
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                                        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
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                                        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>
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                                </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>
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                                        <para>The process, user, and
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                                        group ID of the process the
                                        journal entry originates from
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                                        formatted as a decimal
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                                        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
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                                        path, and the command line of
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                                        the process the journal entry
                                        originates from.</para>
                                </listitem>
                        </varlistentry>

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

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                        <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>
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                                <term><varname>_SYSTEMD_SLICE=</varname></term>
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                                <listitem>
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                                        <para>The control group path
                                        in the systemd hierarchy, the
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                                        systemd session ID (if any),
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                                        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>
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                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>_SELINUX_CONTEXT=</varname></term>
                                <listitem>
                                        <para>The SELinux security
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                                        context (label) of the process
                                        the journal entry originates
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                                        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
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                                        microseconds since the epoch UTC,
                                        formatted as a decimal
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                                        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
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                                        a 128-bit hexadecimal
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                                        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
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                                        service. Valid transports are:
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                                        </para>
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                                        <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>
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                                </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
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                                        device node, separated by <literal>:</literal>
                                        and prefixed by <literal>b</literal>. Similar
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                                        for character devices but
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                                        prefixed by <literal>c</literal>. For network
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                                        devices, this is the interface index
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                                        prefixed by <literal>n</literal>. For all other
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                                        devices, this is the subsystem name
                                        prefixed by <literal>+</literal>, followed by
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                                        <literal>:</literal>, followed by the kernel
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                                        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>
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                <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>
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                <para>Fields used by the <command>systemd-coredump</command>
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                coredump kernel helper:
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                </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
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                                        <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
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                                        </para>
                                </listitem>
                        </varlistentry>
                </variablelist>
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                <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>


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        </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
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                underscores. Note that these are not proper fields when
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                stored in the journal but for addressing metadata of
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                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,
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                                        platforms and journal files.
                                        </para>
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                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>__REALTIME_TIMESTAMP=</varname></term>
                                <listitem>
                                        <para>The wallclock time
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                                        (<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>,
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                                        as it is usually a bit later
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                                        but more likely to be monotonic.
                                        </para>
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                                </listitem>
                        </varlistentry>

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

</refentry>