NFS common errors and troubleshooting - Linux/Unix

I have seen some of the most common NFS Error/Issues which occurs in very common now and then to most of Linux/Unix based system admins. So I decided to put at one palace. Hope this helps most of them.

Environment: Linux/Unix

Error: "Server Not Responding"

Check your NFS server and the client using RPC message and they must be functional/online. 

use ping, traceroute to check are they reaching each other, if not check your NIC using ethtool to verify IP address.

sometimes due to heavy server or network loads causes the RPC message response to time out causing error message. try to increase timeout option.

Error: "rpc mount export: RPC: Timed out " 

NFS server or client was unable to resolve DNS. check forward/reverse DNS name resolution works. 

Check your DNS servers or /etc/hosts

 Error: "Access Denied" or "Permission Denied"

check export permission for the NFS file systems.

#showmount -e nfsserver  ==> client 

#exportfs -a ==> server

check you dont have any syntax issues in file /etc/exports(e.g  space, permissions, typos..etc) 

Error: "RPC: Port mapper failure - RPC: Unable to receive"

NFS requires both NFS service and portmapper service running on both client and the server

#rpcinfo -p

       or

#/etc/init.d/portmap status

if not, start the portmap service

Error: "NFS Stale File Handle"

system call 'open' calls to access NFS file in the same way application uses local file they by returns a file descriptor or handle which programs useses I/O commands to identify the file manipulations

When an NFS file share is either unshared or NFS server changes the file handler, and any NFS client which attempts to do further I/O on the share will receive the 'NFS Stale File Handler'.

on the client :

umount -f /nfsmount or if it is unable to inmount and remount 

kill the processes which uses that /nfsmount

or 

incase if above options didn't work, you can reboot the client to clear the stale NFS.

Error: "No route to host"

this could be reported when client attempts to mount the NFS file system, even when the client can ping them successfully.

This can be due to RPC messages being filtered by either host firewall, client firewall or network switch. verify firewall rules. 

stop suing iptables and try to check the port 2049 

Hope this helps all who might use NFS most of the times. I have figured out these commonly in my experience.

Thanks for sharing !