LOCKF

Section: Linux Programmer's Manual (3)
Updated: 1997-08-06
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NAME

lockf - apply, test or remove a POSIX lock on an open file

SYNOPSIS

#include <sys/file.h>

int lockf(int fd, int cmd, off_t len);

DESCRIPTION

Apply, test or remove a POSIX lock on an open file. The file is specified by fd. This call is just an interface for fcntl(2). Valid operations are given below:

F_LOCK: Set an exclusive lock to the file. Only one process may hold an exclusive lock for a given file at a given time. If the file is already locked it blocks until the previous lock is released.
F_TLOCK: Same as F_LOCK but never blocks and return error instead if the file is already locked.
F_ULOCK: Unlock the file.
F_TEST: Test the lock: return 0 if fd is unlocked or locked by this process; return -1, set errno to EACCES, if another process holds the lock.

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EAGAIN: The file is locked and the LOCK_NB flag was selected, or operation is prohibited because the file has been memory-mapped by another process.
EBADF: fd is not an open file descriptor.
EDEADLK: Specified lock operation would cause a deadlock.
EINVAL: An invalid operation was specified in fd.
ENOLCK: Too many segment locks open, lock table is full.

CONFORMING TO

SYSV

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