Problem

I had an NFS server from which some folders were shared with the client-server. Shared folders were mounted on the client server. Due to some hardware problem in the NFS server, the server suddenly becomes dead and after that when I tried to access the shared folders they were not accessible. When I tried the df command it becomes hanged as shown below:

[root@nfs-client ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              95G   22G   69G  25% /
/dev/sda5              84G  1.1G   79G   2% /var
/dev/sda1             244M   17M  215M   8% /boot
tmpfs                 4.9G     0  4.9G   0% /dev/shm

Reason

This problem occurred because NFS shared folders were not accessible. When I tried to umount to the mounted folders using umount command then it also did not become successful.

Solution

Finally, I removed all mountings using the command umount with -f -l as shown below and after that df command worked fine.

[root@nfs-client ~]# umount -f -l /home/folder1
[root@nfs-client ~]# umount -f -l /home/folder2

[root@nfs-client ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              95G   22G   69G  25% /
/dev/sda5              84G  1.1G   79G   2% /var
/dev/sda1             244M   17M  215M   8% /boot
tmpfs                 4.9G     0  4.9G   0% /dev/shm
[root@nfs-client ~]#

Note: In the above case, the NFS server was an RHEL 6.8 machine and the nfs-client was an RHEL 5.5 machine.