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

       link, linkat - make a new name for a file

       #include <unistd.h>

       int link(const char *oldpath, const char *newpath);

       #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)):

	   Since glibc 2.10:
	       _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
	   Before glibc 2.10:

       link()  creates	a  new link (also known as a hard link) to an existing

       If newpath exists, it will not be overwritten.

       This new name may be used exactly as the old  one  for  any  operation;
       both names refer to the same file (and so have the same permissions and
       ownership) and it is impossible to tell which name was the "original".

       The linkat() system call operates in exactly the same  way  as  link(),
       except for the differences described here.

       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() for a relative pathname).

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

       If oldpath is absolute, then olddirfd is ignored.

       The interpretation of newpath is as for oldpath, except that a relative
       pathname	 is  interpreted  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	refer‐
	      enced  by	 olddirfd  (which  may	have  been  obtained using the
	      open(2) O_PATH flag).  In this case, olddirfd must  refer	 to  a
	      file   other  than  a  directory.	  The  caller  must  have  the
	      CAP_DAC_READ_SEARCH capability in order to use this  flag;  this
	      prevents	arbitrary  users  from	creating hard links using file
	      descriptors received via a UNIX domain socket (see  the  discus‐
	      sion  of	SCM_RIGHTS  in unix(7)).  This flag is Linux-specific;
	      define _GNU_SOURCE to obtain its definition.

       AT_SYMLINK_FOLLOW (since Linux 2.6.18)
	      By default, linkat(), does not dereference oldpath if  it	 is  a
	      symbolic	link (like link()).  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.

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

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

       EACCES Write  access  to the directory containing newpath is denied, or
	      search permission is denied for one of the  directories  in  the
	      path  prefix  of	oldpath	 or  newpath.	(See also path_resolu‐

       EDQUOT The user's quota of disk	blocks	on  the	 filesystem  has  been

       EEXIST newpath already exists.

       EFAULT oldpath or newpath points outside your accessible address space.

       EIO    An I/O error occurred.

       ELOOP  Too many symbolic links were encountered in resolving oldpath or

       EMLINK The file referred to by oldpath already has the  maximum	number
	      of links to it.

	      oldpath or newpath was too long.

       ENOENT A directory component in oldpath or newpath does not exist or is
	      a dangling symbolic link.

       ENOMEM Insufficient kernel memory was available.

       ENOSPC The device containing the file has no room for the new directory

	      A component used as a directory in oldpath or newpath is not, in
	      fact, a directory.

       EPERM  oldpath is a directory.

       EPERM  The filesystem containing oldpath and newpath does  not  support
	      the creation of hard links.

       EPERM (since Linux 3.6)
	      The  caller  does	 not  have permission to create a hard link to
	      this   file   (see   the	 description   of    /proc/sys/fs/pro‐
	      tected_hardlinks in proc(5)).

       EROFS  The file is on a read-only filesystem.

       EXDEV  oldpath  and  newpath  are  not  on the same mounted filesystem.
	      (Linux permits a filesystem to be mounted	 at  multiple  points,
	      but  link() does not work across different mount points, even if
	      the same filesystem is mounted on both.)

       The following additional errors can occur for linkat():

       EBADF  olddirfd or newdirfd is not a valid file descriptor.

       EINVAL An invalid flag value was specified in flags.

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

       ENOENT An  attempt was made to link to the /proc/self/fd/NN file corre‐
	      sponding to a file descriptor created with

		  open(path, O_TMPFILE | O_EXCL, mode);

	      See open(2).

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

       EPERM  AT_EMPTY_PATH was	 specified  in	flags,	oldpath	 is  an	 empty
	      string, and olddirfd refers to a directory.

       linkat() was added to Linux in kernel 2.6.16; library support was added
       to glibc in version 2.4.

       link(): SVr4, 4.3BSD, POSIX.1-2001 (but see NOTES), POSIX.1-2008.

       linkat(): POSIX.1-2008.

       Hard links, as created by link(), cannot span  filesystems.   Use  sym‐
       link(2) if this is required.

       POSIX.1-2001  says  that	 link()	 should dereference oldpath if it is a
       symbolic link.  However, since kernel 2.0, Linux does  not  do  so:  if
       oldpath is a symbolic link, then newpath is created as a (hard) link to
       the same symbolic link file (i.e., newpath becomes a symbolic  link  to
       the  same  file	that  oldpath  refers to).  Some other implementations
       behave in the same manner as Linux.  POSIX.1-2008 changes the  specifi‐
       cation  of  link(),  making  it implementation-dependent whether or not
       oldpath is dereferenced if it is a symbolic link.  For precise  control
       over  the  treatment  of	 symbolic  links  when	creating  a  link, use

       On NFS filesystems, the return code may be wrong in case the NFS server
       performs	 the link creation and dies before it can say so.  Use stat(2)
       to find out if the link got created.

       ln(1), open(2), rename(2), stat(2), symlink(2), unlink(2), path_resolu‐
       tion(7), symlink(7)

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux				  2014-03-19			       LINK(2)

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