A recent update (kernel, or something else) seems to have messed up file locking over NFSv4 on my system (yes, v4 allows for locking). I use locking in perl scripts over NFS and it's always worked until now. I checked and lockd is running on the server still. A test case is at the bottom of this email. The problem hits on line 13 where the open-for-write happens. It dies with "Input/output error". The client's /v/l/messages says: [156474.509107] nfs4_reclaim_open_state: Lock reclaim failed! If I run this on a local file, not over NFS, it works fine. I'm using the lock functions as the sample code in the perl docs instructs. My goal is to lock a file, read it, do things, and write it out, all atomically. Mostly I want to protect against another instance of the same program doing the same thing at the same time and screwing up the file. My NFS server is a an older linux (Fedora 14) than the client (Fedora 16), but the NFSv4 spec hasn't really changed in that span. #!/usr/bin/perl -w # use Fcntl ':flock'; $file='/data/Tmp/locktest'; open(LOCK,$file) or die; flock(LOCK,LOCK_EX); open(IN,$file) or die; # read from file close(IN); open(ORI,">$file") or die $!; # dies here!!!!!!!!!!!!1 # write to file close(ORI); flock(LOCK,LOCK_UN);