LOCKF(3)

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

SEE ALSO
fcntl(2), flock(2)
There are also locks.txt and mandatory.txt in /usr/src/linux/Documentation.