I have NFS4 setup with idmapd working correctly. ls -l from the client shows the correct user names, even though the user ids differ between the machines.

However, when the user ids do not match, I get 'permission denied' errors trying access files, even though ls -l shows the correct username. When the user ids do happen to match by coincidence, everything works fine.

sudo sysctl -w sunrpc.nfsd_debug=1023 gives the following output in the server syslog for the failed file access:

nfsd_dispatch: vers 4 proc 1
nfsv4 compound op #1/3: 22 (OP_PUTFH)
nfsd: fh_verify(28: 00070001 015c0001 00000000 9853d400 2a4892a5 4918a0ba)
nfsv4 compound op ffff88003d0f5078 opcnt 3 #1: 22: status 0
nfsv4 compound op #2/3: 3 (OP_ACCESS)
nfsd: fh_verify(28: 00070001 015c0001 00000000 9853d400 2a4892a5 4918a0ba)
nfsd: fh_verify - just checking
nfsv4 compound op ffff88003d0f5078 opcnt 3 #2: 3: status 0
nfsv4 compound op #3/3: 9 (OP_GETATTR)
nfsd: fh_verify(28: 00070001 015c0001 00000000 9853d400 2a4892a5 4918a0ba)
nfsd: fh_verify - just checking
nfsv4 compound op ffff88003d0f5078 opcnt 3 #3: 9: status 0
nfsv4 compound returned 0
nfsd_dispatch: vers 4 proc 1
nfsv4 compound op #1/7: 22 (OP_PUTFH)
nfsd: fh_verify(28: 00070001 015c0001 00000000 9853d400 2a4892a5 4918a0ba)
nfsv4 compound op ffff88003d0f5078 opcnt 7 #1: 22: status 0
nfsv4 compound op #2/7: 32 (OP_SAVEFH)
nfsv4 compound op ffff88003d0f5078 opcnt 7 #2: 32: status 0
nfsv4 compound op #3/7: 18 (OP_OPEN)
NFSD: nfsd4_open filename dom_file op_stateowner (null)
renewing client (clientid 4f96587d/0000000e)
nfsd: nfsd_lookup(fh 28: 00070001 015c0001 00000000 9853d400 2a4892a5 4918a0ba, dom_file)
nfsd: fh_verify(28: 00070001 015c0001 00000000 9853d400 2a4892a5 4918a0ba)
nfsd: fh_verify - just checking
nfsd: fh_lock(28: 00070001 015c0001 00000000 9853d400 2a4892a5 4918a0ba) locked = 0 
nfsd: fh_compose(exp 08:01/22806529 srv/dom_file, ino=22809724)
nfsd: fh_verify(36: 01070001 015c0001 00000000 9853d400 2a4892a5 4918a0ba)
nfsd: fh_verify - just checking
fh_verify: srv/dom_file permission failure, acc=804, error=13
nfsv4 compound op ffff88003d0f5078 opcnt 7 #3: 18: status 13
nfsv4 compound returned 13

Is that useful to anyone? Any hints on to debug this would be greatly appreciated.

Server kernel: 2.6.32-40-server (Ubuntu 10.04)
Client kernel: 3.2.0-27-generic (Ubuntu 12.04)

Same problem with my new server running 3.2.0-27-generic (Ubuntu 12.04).

Thanks.