A mounted NFS filesystem cannot be accessed (permission denied) when the server is back online after a reboot (crash). To reproduce the error: - NFS mount a filesystem - 'ls <filesystem>' to check it works - Reboot the server - 'ls <filesystem>' hangs (correct behaviour) when the server is off and returns 'permission denied' (wrong behaviour) after the server has become online. This is seen no matter you are using 'hard' or 'soft' option for the NFS mount. Note that the behaviour is NOT normal. Reading from 'man mount' in the section 'Mount options for nfs', option 'hard' you get in fact: "When the NFS server is back online the program will continue undisturbed from where it was." Indeed this is what should happen, since NFS is a stateless protocol.
Works for me... What kernel are you running?
I've met this on one occasion only. When it occurred, I discovered that the server grabbed its IP address via BOOTP and had been given a different IP address when it rebooted after crashing. I would imagine a similar problem would occur if one was accessing the NFS server through a masquerading firewall with a Dynamic IP link out.