+ <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>Special Journal Fields</title>
+
+ <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>systemd-coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
+ </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 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>