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NAME

     link, linkat - make a hard file link

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     int
     link(const char *name1, const char *name2);

     int
     linkat(int fd1, const char *name1, int fd2, const char *name2, int flag);

DESCRIPTION

     The link() system call atomically creates the specified directory entry
     (hard link) name2 with the attributes of the underlying object pointed at
     by name1.  If the link is successful: the link count of the underlying
     object is incremented; name1 and name2 share equal access and rights to
     the underlying object.

     If name1 is removed, the file name2 is not deleted and the link count of
     the underlying object is decremented.

     The object pointed at by the name1 argument must exist for the hard link
     to succeed and both name1 and name2 must be in the same file system.  The
     name1 argument may not be a directory.

     The linkat() system call is equivalent to link except in the case where
     either name1 or name2 or both are relative paths.  In this case a
     relative path name1 is interpreted relative to the directory associated
     with the file descriptor fd1 instead of the current working directory and
     similarly for name2 and the file descriptor fd2.

     Values for flag are constructed by a bitwise-inclusive OR of flags from
     the following list, defined in

     AT_SYMLINK_FOLLOW
             If name1 names a symbolic link, a new link for the target of the
             symbolic link is created.

     If linkat() is passed the special value AT_FDCWD in the fd1 or fd2
     parameter, the current working directory is used for the respective name
     argument.  If both fd1 and fd2 have value AT_FDCWD, the behavior is
     identical to a call to link().  Unless flag contains the
     AT_SYMLINK_FOLLOW flag, if name1 names a symbolic link, a new link is
     created for the symbolic link name1 and not its target.

RETURN VALUES

     The link() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS

     The link() system call will fail and no link will be created if:

     [ENOTDIR]          A component of either path prefix is not a directory.

     [ENAMETOOLONG]     A component of either pathname exceeded 255
                        characters, or entire length of either path name
                        exceeded 1023 characters.

     [ENOENT]           A component of either path prefix does not exist.

     [EOPNOTSUPP]       The file system containing the file named by name1
                        does not support links.

     [EMLINK]           The link count of the file named by name1 would exceed
                        32767.

     [EACCES]           A component of either path prefix denies search
                        permission.

     [EACCES]           The requested link requires writing in a directory
                        with a mode that denies write permission.

     [ELOOP]            Too many symbolic links were encountered in
                        translating one of the pathnames.

     [ENOENT]           The file named by name1 does not exist.

     [EEXIST]           The link named by name2 does exist.

     [EPERM]            The file named by name1 is a directory.

     [EPERM]            The file named by name1 has its immutable or append-
                        only flag set, see the chflags(2) manual page for more
                        information.

     [EPERM]            The parent directory of the file named by name2 has
                        its immutable flag set.

     [EXDEV]            The link named by name2 and the file named by name1
                        are on different file systems.

     [ENOSPC]           The directory in which the entry for the new link is
                        being placed cannot be extended because there is no
                        space left on the file system containing the
                        directory.

     [EDQUOT]           The directory in which the entry for the new link is
                        being placed cannot be extended because the user’s
                        quota of disk blocks on the file system containing the
                        directory has been exhausted.

     [EIO]              An I/O error occurred while reading from or writing to
                        the file system to make the directory entry.

     [EROFS]            The requested link requires writing in a directory on
                        a read-only file system.

     [EFAULT]           One of the pathnames specified is outside the
                        process’s allocated address space.

     In addition to the errors returned by the link(), the linkat() system
     call may fail if:

     [EBADF]            The name1 or name2 argument does not specify an
                        absolute path and the fd1 or fd2 argument,
                        respectively, is neither AT_FDCWD nor a valid file
                        descriptor open for searching.

     [EINVAL]           The value of the flag argument is not valid.

     [ENOTDIR]          The name1 or name2 argument is not an absolute path
                        and fd1 or fd2, respectively, is neither AT_FDCWD nor
                        a file descriptor associated with a directory.

SEE ALSO

     chflags(2), readlink(2), symlink(2), unlink(2)

STANDARDS

     The link() system call is expected to conform to ISO/IEC 9945-1:1990
     (“POSIX.1”).  The linkat() system call follows The Open Group Extended
     API Set 2 specification.

HISTORY

     The link() function appeared in Version 7 AT&T UNIX.  The linkat() system
     call appeared in FreeBSD 8.0.

     The link() system call traditionally allows the super-user to link
     directories which corrupts the file system coherency.  This
     implementation no longer permits it.