NooB Assitance with debugging NFSv4 client requested

[Tim Watts <t.watts@imperial.ac.uk>]

Hi,

I have an NFSv4 client set up on Ubuntu 10.04.1 LTS x86. The NFSv4 
server is running Centos 5.5 and we use MIT kerberos and LDAP for 
users/groups. This seems to work well with Centos 5.5 clients

All works fine with my Ubuntu client, except after a while my client 
acts like it loses its authentication - symptom: home directory mount 
drops to "nobody" - I see the mount as "other" - no write access, can 
read files that have world read bit set etc.

This can happen anytime between 48 hours and 2 hours after a full client 
reboot. It seems to be triggered by active use of thunderbird via the 
NFSv4 mounted home dir which suggests it may be load sensitive.

When it happens, if I unmount my home dir (killing the desktop of 
course) , then remount the fault is cleared and I can work again.

What doesn't work is just doing a kinit -f or restarting idmapd or gssd.

I have run rpc.gssd in foreground debug mode and that doesn't say much 
during the problem times, ditto idmapd. We are using openldap for passwd 
and group lookups cached locally with nscd.

I have tried upping kernel debugging:

rpcdebug -m nfs -s vfs dircache lookupcache pagecache proc xdr file root 
callback client mount all

but I'm not sure what I'm looking for.

The symptoms feel like the kernel is losing the ticket or timing it out 
or possibly the ID mapping is failing - is there any way to examining 
the state of the kernel ticket cache or anything else I could be looking 
for?

I am tempted to say this is a bug, possibly in the Ubuntu build, but I 
would like to investigate further.

Any pointers much appreciated as to how I might isolate the fault further.

Cheers

Tim
-- 
Tim Watts