Exclusive locking of a file on an NFS filesystem

[rah]

Monks,

Does anyone know of a way I can put an exlusive lock on a file in an NFS filesystem, shared by just a couple of nodes. I have two processes on boxes which have the FS mounted. Basically I want the first one there, to win exclusive access to the file.

I have super searched and googled and did come up with File::NFSlock, but the readme is rather terse. It mentions an exclusive mode, but I can't tell if it allows this lock on read. I am going to pull it down tomorrow and test. But I was wondering if any monks have done this. Can it be done?

[SarahM]

I've tried File::NFSlock, but it didn't work that well for me...It was great during my testing. But when actual workload hit it, the locking didn't detect the file as locked too many times to be useful and I ended up having messed up files.

On Solaris, I've also turned on rpc.lockd and rpc.statd. This seemed to work, except when one of the boxes crashed. It took a couple of hours and several reboots of both boxes before my sys admin was able to clear the outstanding locks.

Locking over NFS seems to be problematic at best.

[Abigail-II]

Whether you can reliably lock a file over NFS depends on the implementation of NFS on the involved systems. In general, you should avoid using locking over NFS - it's certainly not going to be portable.

Abigail

[Anonymous Monk]

File::lockf

[robobunny]

you might consider implementing something similar to what the 'lockfile' command that comes with procmail does, or using lockfile itself.

[rah]

Thanks all for your replies. I don't need to worry about poratability (for now anyway), and my set up will be relatively simple. Two linux boxes looking for a "command" file in a directory NFS mounted from an AIX box. The program picking up this file and passing it off to a FAX program will likely be perl. If one of the available modules looked to be feasible for this set up, I would try it. If not, there are a number of other approaches we could take, including something akin to what procmail does. In fact, it seems like we have implemented that scheme many times.