NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

       #include <sys/file.h>

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

DESCRIPTION    [Toc]    [Back]

       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    [Toc]    [Back]

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

ERRORS    [Toc]    [Back]

       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    [Toc]    [Back]
	      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    [Toc]    [Back]

       SYSV

SEE ALSO    [Toc]    [Back]

       fcntl(2), flock(2)
       There are also locks.txt and mandatory.txt in /usr/src/linux/Documenta-
       tion.



Linux 2.0			  1997-08-06			      LOCKF(3)