+ systemd-logind, instead.</para>
+
+ <para>These functions access data in
+ <filename>/proc</filename>,
+ <filename>/sys/fs/cgroup</filename> and
+ <filename>/run</filename>. All of these are virtual
+ file systems, hence the runtime cost of the accesses
+ is relatively cheap.</para>
+
+ <para>If the functions return string arrays, these are
+ generally NULL terminated and need to be freed by the
+ caller with the libc
+ <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ call after use, including the strings referenced
+ therein. Similar, individual strings returned need to
+ be freed, as well.</para>
+
+ <para>As a special exception, instead of an empty
+ string array NULL may be returned, which should be
+ treated equivalent to an empty string array.</para>