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Linux 2.0
6 August 1997

manpages-pt-dev

Portuguese Versions of the Manual Pages (dev sections)

manpages-dev

Manual pages about using GNU/Linux for development

man-pages

Linux kernel and C library user-space interface documentation

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.
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