The Solaris 2.5 release also included an improved version of the network lock manager. The network lock manager provided UNIX record locking and PC file sharing for NFS files. The locking mechanism is now more reliable for NFS files, so commands that use locking are less likely to hang.
The Network Lock Manager is used only for NFS version 2 and version 3 mounts. File locking is built into the NFS version 4 protocol.