+.B \-H " or " \-\-ha-callout prog
+Specify a high availability callout program, which will receive callouts
+for all client mount and unmount requests. This allows
+.B rpc.mountd
+to be used in a High Availability NFS (HA-NFS) environment. This callout is not
+needed (and should not be used) with 2.6 and later kernels (instead,
+mount the nfsd filesystem on
+.B /proc/fs/nfsd
+).
+The program will be called with 4 arguments.
+The first will be
+.B mount
+or
+.B unmount
+depending on the reason for the callout.
+The second will be the name of the client performing the mount.
+The third will be the path that the client is mounting.
+The last is the number of concurrent mounts that we believe the client
+has of that path.
+.TP