Find Out NFS Clients Connected To My NFS Server

You can use the following commands. SSH or login into your nfs server and type the following command:

netstat -an | grep nfs.server.ip:port

If your nfs server IP address 192.168.1.12 and port is 2049, enter:

netstat -an | grep 192.168.1.12:2049

Sample outputs:

tcp 0 0 192.168.1.12:2049 192.168.1.5:757 ESTABLISHED
tcp 0 0 192.168.1.12:2049 192.168.1.6:892 ESTABLISHED

Where,

192.168.1.12 – NFS serer IP address
2049 – NFS server port
192.168.1.5 and 192.168.1.6 – NFS clients IP address

showmount command

You can to use the showmount command to see mount information for an NFS server. The following command should not be used as it may produce unreliable result (you can type this command on any one of the nfs client):

showmount -a nas03

Sample outputs:

All mount points on nas03:
192.168.1.101:/volume1/data
192.168.1.102:/volume1/data
192.168.1.103:/volume1/data
192.168.1.5:/volume1/data
192.168.1.6:/volume1/data

Where,

-a : List both the client hostname or IP address and mounted directory in host:dir format. This info should not be considered reliable.

More about /var/lib/nfs/rmtab file

The rmtab file is located at /var/lib/nfs/rmtab on nfs server and can be viewed using the cat command:

cat /var/lib/nfs/rmtab

From the rpc.mountd(8) man page:

The rpc.mountd daemon registers every successful MNT request by adding an entry to the /var/lib/nfs/rmtab file. When receivng a UMNT request from an NFS client, rpc.mountd simply removes the matching entry from /var/lib/nfs/rmtab, as long as the access control list for that export allows that sender to access the export.

Clients can discover the list of file systems an NFS server is currently exporting, or the list of other clients that have mounted its exports, by using the show- mount(8) command. showmount(8) uses other procedures in the NFS MOUNT protocol to report information about the servers exported file systems.

Note, however, that there is little to guarantee that the contents of /var/lib/nfs/rmtab are accurate. A client may continue accessing an export even after invoking UMNT. If the client reboots without sending a UMNT request, stale entries remain for that client in /var/lib/nfs/rmtab.

Src: https://www.cyberciti.biz/faq/appleosx-bsd-find-clients-connecting-to-a-nfsserver/