showmount lists all the clients that have remotely mounted a
filesystem from host. This information is maintained by the
server on host, and is saved across crashes in the file
/etc/rmtab. The default value for host is the value
Print all remote mounts in the format:
hostname : directory
where hostname is the name of the client, and directory
is the root of the filesystem that has been mounted.
List directories that have been remotely mounted by clients.
Print the list of exported filesystems.
If a client crashes, its entry will not be removed from the list until it
reboots and executes umount -a.