In what way is fcntl.lockf() locking a file?

Question

I'm currently attempting to lock a file via python so other processes cannot even read it.

So far i was testing behavior of fcntl.lockf() via python interpreter:

>>> file = open("/path/to/file", "w")
>>> fcntl.lockf(file.fileno(), fcntl.LOCK_EX | fcntl_LOCK_READ)

I've tried this and few other variations of fcntl.lockf but still i was able to open the file second time and obtain his fd. I was able to read it and also write to it.

Am I missing something or this should not lock the file for other procesess at all? Is there any other way to do it?

Answer 1

It is an advisory lock, that is only a cooperating process will be deterred. See this discussion on how to place a mandatory lock.