Lustre 1.6 Operations Manual

32.5.7 Flock Feature
Lustre now includes the flock feature, which provides file locking support. Flock
describes classes of file locks known as ‘flocks’. Flock can apply or remove a lock on
an open file as specified by the user. However, a single file may not, simultaneously,
have both shared and exclusive locks.
By default, the flock utility is disabled on Lustre. Two modes are available.
local mode
consistent mode
In this mode, locks are coherent on a node (a single-node flock), but not
across all clients. To enable it, use -o localflock.
This is a client-mount option.
In this mode, locks are coherent across all clients.
To enable it, use the -o flock. This is a client-mount option.
CAUTION: This mode has a noticeable performance impact and may
affect stability, depending on the Lustre version used. Consider using a
newer Lustre version which is more stable.
A call to use flock may be blocked if another process is holding an incompatible
lock. Locks created using flock are applicable for an open file table entry. Therefore,
a single process may hold only one type of lock (shared or exclusive) on a single file.
Subsequent flock calls on a file that is already locked converts the existing lock to the
new lock mode.
32.5.7.1 Example
$ mount -t lustre –o flock mds@tcp0:/lustre /mnt/client
You can check it in /etc/mtab. It should look like,
mds@tcp0:/lustre /mnt/client lustre rw,flock 00
Chapter 32 System Configuration Utilities (man8) 32-21