This usually happened when the nfs server is down, you cannot umount the nfs mount, because the system will say "not found or server not reachable"
$ sudo umount /opt/logs/production umount.nfs: nfs.local:/var/lib/backup: not found / mounted or server not reachable umount.nfs: nfs.local:/var/lib/backup: not found / mounted or server not reachable
To fix this, you need to force mount it with lazy flag:
$ sudo umount -f -l /opt/logs/productionwhere -f is to do force unmount, and -l is for lazy unmounting. From man:
"Lazy unmount. Detach the filesystem from the filesystem hierarchy now, and cleanup all references to the filesystem as soon as it is not busy anymore."
That's all folks.