Stop and Start NFS and Related Services

Using restart option (i.e. service nfs restart) may crash / freeze your Linux computer if executed.

Stop NFS server:  

# service nfslock stop
# service nfs stop
# service portmap stop
# umount /proc/fs/nfsd

Start service in following order:
# service portmap start
# service nfs start
# service nfslock start
# mount -t nfsd nfsd /proc/fs/nfsd