- <para>Note that <function>sd_id128_get_boot()</function> always
- returns a UUID v4 compatible ID.
- <function>sd_id128_get_machine()</function> will also return a
- UUID v4-compatible ID on new installations but might not on older.
- It is possible to convert the machine ID into a UUID v4-compatible
+ <para><function>sd_id128_get_invocation()</function> returns the invocation ID of the currently executed
+ 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>
+
+ <para>Note that <function>sd_id128_get_boot()</function> and <function>sd_id128_get_invocation()</function> always
+ return UUID v4 compatible IDs. <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible
+ ID on new installations but might not on older. It is possible to convert the machine ID into a UUID v4-compatible