Unix/Linux Go Back    


Linux 2.6 - man page for lockf (linux section 3)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


LOCKF(3)			    Linux Programmer's Manual				 LOCKF(3)

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

SYNOPSIS
       #include <unistd.h>

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       lockf():
	   _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
	   _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION
       Apply, test or remove a POSIX lock on a section of an open file.  The file is specified by
       fd,  a  file  descriptor  open for writing, the action by cmd, and the section consists of
       byte positions pos..pos+len-1 if len is positive, and pos-len..pos-1 if len  is	negative,
       where  pos  is the current file position, and if len is zero, the section extends from the
       current file position to infinity, encompassing the present and future  end-of-file  posi-
       tions.  In all cases, the section may extend past current end-of-file.

       On  Linux,  lockf()  is	just an interface on top of fcntl(2) locking.  Many other systems
       implement lockf() in this way, but note that POSIX.1-2001 leaves the relationship  between
       lockf() and fcntl(2) locks unspecified.	A portable application should probably avoid mix-
       ing calls to these interfaces.

       Valid operations are given below:

       F_LOCK Set an exclusive lock on the specified section of the file.  If (part of) this sec-
	      tion  is	already  locked, the call blocks until the previous lock is released.  If
	      this section overlaps an earlier locked section, both are merged.  File  locks  are
	      released	as  soon as the process holding the locks closes some file descriptor for
	      the file.  A child process does not inherit these locks.

       F_TLOCK
	      Same as F_LOCK but the call never blocks and returns an error instead if	the  file
	      is already locked.

       F_ULOCK
	      Unlock  the  indicated  section of the file.  This may cause a locked section to be
	      split into two locked sections.

       F_TEST Test the lock: return 0 if the specified section is  unlocked  or  locked  by  this
	      process;	return -1, set errno to EAGAIN (EACCES on some other systems), if another
	      process holds a lock.

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

ERRORS
       EACCES or EAGAIN
	      The file is locked and F_TLOCK or F_TEST was specified, or the operation is prohib-
	      ited because the file has been memory-mapped by another process.

       EBADF  fd  is  not  an  open  file descriptor; or cmd is F_LOCK or F_TLOCK and fd is not a
	      writable file descriptor.

       EDEADLK
	      The command was F_LOCK and this 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
       SVr4, POSIX.1-2001.

SEE ALSO
       fcntl(2), flock(2)

       locks.txt and mandatory-locking.txt  in	the  Linux  kernel  source  directory  Documenta-
       tion/filesystems  (on  older  kernels,  these  files  are directly under the Documentation
       directory, and mandatory-locking.txt is called mandatory.txt)

COLOPHON
       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

GNU					    2012-07-07					 LOCKF(3)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 03:08 PM.