- service. In its current implementation, this reads and parses the <varname>$INVOCATION_ID</varname> environment
- variable that the service manager sets when activating a service, see
- <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The
- ID is cached internally. In future a different mechanism to determine the invocation ID may be added.</para>
+ service. In its current implementation, this tries to read and parse the following:
+ <itemizedlist>
+ <listitem>
+ <para>The <varname>$INVOCATION_ID</varname> environment variable that the service manager sets when
+ activating a service.</para>
+ </listitem>
+ <listitem>
+ <para>An entry in the kernel keyring that the system service manager sets when activating a service.
+ </para>
+ </listitem>
+ </itemizedlist>
+ See <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details. The ID is cached internally. In future a different mechanism to determine the invocation ID
+ may be added.</para>