This command displays a stack trace for each process. The pstack command must be run by the owner of the process or by root. You can use pstack to determine where a process is hung. The only option that is allowed with this command is the PID of the process that you want to check. See the proc(1) man page.
The following example 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
The example shows that the process is waiting for a new connection request, which is a normal response. If the stack shows that the process is still in poll after a request is made, the process might be 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.