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
              referenced 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_TMPFILE
              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
       to indicate the error.

       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

       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 links.

              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/protected_hardlinks in

       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 mounts, even if the same
              filesystem is mounted on both.)

       The following additional errors can occur for linkat():

       EBADF  oldpath (newpath) is relative but olddirfd (newdirfd) is neither
              AT_FDCWD nor 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).

       ENOENT An attempt was made to link to a /proc/self/fd/NN file
              corresponding to a file that has been deleted.

       ENOENT oldpath is a relative pathname and olddirfd refers to a directory
              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 newdirfd

       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
       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().

   Glibc notes
       On older kernels where linkat() is unavailable, the glibc wrapper
       function falls back to the use of link(), unless the AT_SYMLINK_FOLLOW is
       specified.  When oldpath and newpath are relative pathnames, glibc
       constructs 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_resolution(7), symlink(7)

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       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                              2021-08-27                            LINK(2)