This (Lustre) filesystem doesn't support locking
Lustre does support file locking, even between clients, it just doesn't enable this by default because of overhead. If your application is running on only a single node, you can mount the Lustre client using the -o localflock
mount option, which enables flock but it is not coherent across client nodes. This is the fastest if you only need flock for a single-node application.
If you need flock to be coherent between an application running on multiple client nodes at the same time, mount all of the involved clients with the -o flock
mount option.