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NAME

       link, linkat - make a new name for a file

SYNOPSIS

       #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)):

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

DESCRIPTION

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

       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".

   linkat()
       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
              referenced  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
              discussion  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().

RETURN VALUE

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

ERRORS

       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_resolution(7).)

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

       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
              newpath.

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

       ENAMETOOLONG
              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
              entry.

       ENOTDIR
              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/protected_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
              corresponding to a file descriptor created with

                  open(path, O_TMPFILE | O_EXCL, mode);

              See open(2).

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

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

VERSIONS

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

CONFORMING TO

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

       linkat(): POSIX.1-2008.

NOTES

       Hard links,  as  created  by  link(),  cannot  span  filesystems.   Use
       symlink(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
       specification  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
       linkat(2).

BUGS

       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.

SEE ALSO

       ln(1),   open(2),   rename(2),    stat(2),    symlink(2),    unlink(2),
       path_resolution(7), symlink(7)

COLOPHON

       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 http://www.kernel.org/doc/man-pages/.



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