Troubleshooting "No locks available" errors on NFS v3 shares

Issue

• Why acquiring an exclusive lock on a NFS share, returns "No locks available"?
  • NFS client can not lock files using NFSv3.
  • NFS client can lock a file using NFSv4.x
  • Packet capture shows no NLM LOCK Calls.

• The flock command fails to find locks.

  # flock  "/mnt/test.txt" --command "echo file locked"
  flock: /mnt/test.txt: No locks available