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LINKAT(2)			    Linux Programmer's Manual				LINKAT(2)

NAME
       linkat - create a file link relative to directory file descriptors

SYNOPSIS
       #include <fcntl.h> /* Definition of AT_* constants */
       #include <unistd.h>

       int linkat(int olddirfd, const char *oldpath,
		  int newdirfd, const char *newpath, int flags);

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

       linkat():
	   Since glibc 2.10:
	       _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
	   Before glibc 2.10:
	       _ATFILE_SOURCE

DESCRIPTION
       The  linkat() system call operates in exactly the same way as link(2), except for the dif-
       ferences described in this manual page.

       If the pathname given in oldpath is relative, then  it  is  interpreted	relative  to  the
       directory referred to by the file descriptor olddirfd (rather than relative to the current
       working directory of the calling process, as is done by link(2) for a relative pathname).

       If oldpath is relative and olddirfd is the special value AT_FDCWD, then oldpath is  inter-
       preted relative to the current working directory of the calling process (like link(2)).

       If oldpath is absolute, then olddirfd is ignored.

       The interpretation of newpath is as for oldpath, except that a relative pathname is inter-
       preted relative to the directory referred to by the file descriptor newdirfd.

       The following values can be bitwise ORed in flags:

       AT_EMPTY_PATH (since Linux 2.6.39)
	      If oldpath is an empty string, create a link to the  file  referenced  by  olddirfd
	      (which  may  have been obtained using the open(2) O_PATH flag).  In this case, old-
	      dirfd can refer to any type of file, not just a directory.  The  caller  must  have
	      the  CAP_DAC_READ_SEARCH	capability in order to use this flag; this prevents arbi-
	      trary users from creating hard links using file descriptors  received  via  a  UNIX
	      domain socket (see the discussion of SCM_RIGHTS in unix(7)).

       AT_SYMLINK_FOLLOW (since Linux 2.6.18)
	      By  default,  linkat(), does not dereference oldpath if it is a symbolic link (like
	      link(2)).  The flag AT_SYMLINK_FOLLOW can be specified in flags to cause oldpath to
	      be dereferenced if it is a symbolic link.

       Before kernel 2.6.18, the flags argument was unused, and had to be specified as 0.

RETURN VALUE
       On success, linkat() returns 0.	On error, -1 is returned and errno is set to indicate the
       error.

ERRORS
       The same errors that occur for link(2) can also occur for linkat().  The  following  addi-
       tional errors can occur for linkat():

       EBADF  olddirfd or newdirfd is not a valid file descriptor.

       ENOENT AT_EMPTY_PATH   was   specified	in  flags,  but  the  caller  did  not	have  the
	      CAP_DAC_READ_SEARCH capability.

       ENOTDIR

       ENOTDIR
	      oldpath is relative and olddirfd is a file descriptor referring  to  a  file  other
	      than a directory; or similar for newpath and newdirfd

VERSIONS
       linkat()  was  added to Linux in kernel 2.6.16; library support was added to glibc in ver-
       sion 2.4.

CONFORMING TO
       POSIX.1-2008.

NOTES
       See openat(2) for an explanation of the need for linkat().

SEE ALSO
       link(2), openat(2), path_resolution(7), symlink(7)

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/.

Linux					    2013-07-21					LINKAT(2)
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