"When a program attempts to lock a file with lockf or fcntl that has mandatory locking set, the kernel will prevent all other programs from accessing the file.[1] Processes which use flock will not trigger a mandatory lock."
"To prevent mandatory locking from taking over the entire filesystem, only specifically tagged files will exhibit mandatory locks. The way you define a file to be governed by mandatory locks is to set the sgid (setgroupid) bit, but not the group execute bit. This combination doesn't make any sense normally,[2] which is why it was chosen for this purpose."
… "incontournables" … dans des limites bien définies…