<refsect1>
<title>Return Value</title>
- <para>The two calls return 0 on success (in which case
- <parameter>ret</parameter> is filled in), or a negative
- errno-style error code.</para>
+ <para>Those calls return 0 on success (in which case <parameter>ret</parameter> is filled in),
+ or a negative errno-style error code. In particular, <function>sd_id128_get_machine()</function>
+ and <function>sd_id128_get_machine_app_specific()</function> return <constant>-ENOENT</constant>
+ if <filename>/etc/machine-id</filename> is missing, and <constant>-ENOMEDIUM</constant> if is
+ empty or all zeros.</para>
</refsect1>
<refsect1>