Restart to solve NFS Unknown error 521

I just had Unknown error 521 while mounting NFS version 3 on a Debian server after a reboot. Solving it took me some time but the solution was very easy.

My setup is NFS server on storage server running Debian and a NFS client on another Debian machine where connecting to the NFS server. After a long period of time i made a reboot on my client machine and got mount.nfs: Unknown error 521

My /etc/fstab is as follow:

1.2.3.4:/srv/nfs/web1/mail /var/mail    nfs      nfsvers=3,rw,async,hard,fsc,intr  0     0

I could mount it running version 4 but in verion 3 i got the error.

When i tried with -v option i got the following output:

mount.nfs -o vers=3 1.2.3.4:/srv/nfs/web1/mail /var/mail -v
mount.nfs: timeout set for Mon Sep 22 17:25:16 2014
mount.nfs: trying text-based options 'vers=3,addr=1.2.3.4'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying 1.2.3.4 prog 100003 vers 3 prot TCP port 38467
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying 1.2.3.4 prog 100005 vers 3 prot UDP port 47766
mount.nfs: mount(2): Unknown error 521
mount.nfs: Unknown error 521

The simple solution was to restart the NFS server service.

On my NFS Server i did:

/etc/init.d/nfs-kernel-server restart

After that i got my NFS client to connect with version 3 on the NFS server without any errors.

mount.nfs -o vers=3 1.2.3.4:/srv/nfs/web1/mail /var/mail -v
mount.nfs: timeout set for Mon Sep 22 17:28:15 2014
mount.nfs: trying text-based options 'vers=3,addr=1.2.3.4'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying 1.2.3.4 prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying 1.2.3.4 prog 100005 vers 3 prot UDP port 54305

I hope this will help someone solve this issue faster then me.

Nikola Stojanoski

System Administrator and Developer. Giving back to the community by blogging about my problems, solutions and practical howto's.