man: document the nfs mount option bg as unsupported (#3231)

The nfs mount option bg will not be supported with systemd.

Reasons are discussed here:
https://github.com/systemd/systemd/pull/3169

diff --git a/man/systemd.mount.xml b/man/systemd.mount.xml
index bf56a49e589ffd6ae36f71bff6edc6fe5a0faf14..66cddd72e0670b310f7301ffab7011aa4dcae9ec 100644 (file)
--- a/man/systemd.mount.xml
+++ b/man/systemd.mount.xml
@@ -159,6 +159,11 @@
     <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
     for details about the conversion.</para>
 
+    <para>The NFS mount option <option>bg</option> for NFS background mounts
+    as documented in <citerefentry><refentrytitle>nfs</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    is not supported in <filename>/etc/fstab</filename> entries. The systemd mount option <option>nofail</option>
+    provides similar functionality and should be used instead.</para>
+
     <para>When reading <filename>/etc/fstab</filename> a few special
     mount options are understood by systemd which influence how
     dependencies are created for mount points. systemd will create a