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:
               _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 can refer  to  any
              type  of  file except a directory.  This will generally not work
              if the file has a link count of zero (files created with  O_TMP-
              FILE and without O_EXCL are an exception).  The caller must have
              the CAP_DAC_READ_SEARCH capability in order to  use  this  flag.
              This  flag  is  Linux-specific; define _GNU_SOURCE to obtain its

       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.  If procfs is mounted, this can be used as an
              alternative to AT_EMPTY_PATH, like this:

                  linkat(AT_FDCWD, "/proc/self/fd/<fd>", newdirfd,
                         newname, AT_SYMLINK_FOLLOW);

       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 ex-

       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.  For example, on an ext4(5) filesystem that does
              not  employ  the  dir_index  feature, the limit on the number of
              hard links to a file is 65,000; on btrfs(5), the limit is 65,535

              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)).

       EPERM  oldpath    is    marked    immutable   or   append-only.    (See

       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).

       ENOENT oldpath  is  a relative pathname and olddirfd refers to a direc-
              tory that has been deleted, or newpath is  a  relative  pathname
              and newdirfd refers to a directory that has been deleted.

              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  be-
       have  in the same manner as Linux.  POSIX.1-2008 changes the specifica-
       tion of link(), making it implementation-dependent whether or not  old-
       path  is  dereferenced  if  it is a symbolic link.  For precise control
       over the  treatment  of  symbolic  links  when  creating  a  link,  use

   Glibc notes
       On older kernels where linkat() is unavailable, the glibc wrapper func-
       tion falls back to the use of link(), unless the  AT_SYMLINK_FOLLOW  is
       specified.  When oldpath and newpath are relative pathnames, glibc con-
       structs pathnames based on the symbolic  links  in  /proc/self/fd  that
       correspond to the olddirfd and newdirfd arguments.

       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 5.07 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at

Linux                             2017-09-15                           LINK(2)

Man(1) output converted with man2html
list of all man pages