Problems umount-ing dead NFS

[Jeremy Tay]

Hi everybody,

I am very confused about how to actually unmount a NFS filesystem that
has gone stray. I am currently writing a script that switches between
the main and backup servers according to their state, but when testing
it, everything seems to halt at unmounting the dead fs.

I tested it by mounting an export on a client, and then changing the
server's IP address or switching it completely off. When umount (or
umount -f) is called on the client to detach the dead filesystem before
mounting the export of the backup server, it stood still.

Some googling informed me that rebooting is the only way to get rid of
the stale fs but others say that a umount -f should free up the mount if
it is mounted soft. The flags I use are -3isl -R1 -t5 -D5 -r32768
-w32768 and still I can't unmount it.

Please give me a hand... any help would be appreciated.

- Jeremy