LOCKF(F)            Linux Programmer's Manual            LOCKF(F)



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(l).  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(l), flock(k)
       There   are   also   locks.txt   and   mandatory.txt    in
       /usr/src/linux/Documentation.



Linux 2.0                   1997-08-06                   LOCKF(F)