pstack

This command displays a stack trace for each process. It must be run by root. You can use it to determine where a process is hung. The only option allowed with this command is the PID of the process that you want to check (see the proc(1) man page).

The example below is checking the nfsd process that is running.

# /usr/proc/bin/pstack 243
243:    /usr/lib/nfs/nfsd -a 16
 ef675c04 poll     (24d50, 2, ffffffff)
 000115dc ???????? (24000, 132c4, 276d8, 1329c, 276d8, 0)
 00011390 main     (3, efffff14, 0, 0, ffffffff, 400) + 3c8
 00010fb0 _start   (0, 0, 0, 0, 0, 0) + 5c

It shows that the process is waiting for a new connection request. This is a normal response. If the stack shows that the process is still in poll after a request is made, it is possible that the process is hung. Follow the instructions in "How to Restart NFS Services" to fix this problem. Review the instructions in "NFS Troubleshooting Procedures" to fully verify that your problem is a hung program.