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 <fcntl.h>:

     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.

     [EINTEGRITY]       Corrupted data was detected while reading from the file system.

     [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 1 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.