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