linkat(2) - NetBSD Manual Pages

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LINK(2)                   NetBSD System Calls Manual                   LINK(2)


NAME

     link -- make a hard file link


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <unistd.h>

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

     #include <fcntl.h>

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


DESCRIPTION

     The link() function 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.

     name1 must exist for the hard link to succeed and both name1 and name2
     must be in the same file system.  name1 may not be a directory unless the
     caller is the super-user and the file system containing it supports link-
     ing to directories.

     linkat() works the same way as link() except if name1 (resp.  name2) is
     relative.  In that case, it is looked up from a directory whose file
     descriptor was passed as fd1 (resp.  fd2).  Search permission is required
     on the directories named by fd1 and fd2.  fd1 or fd2 can be set to
     AT_FDCWD in order to specify the current directory.

     When operating on a symlink, link() resolves the symlink and creates a
     hard link on the target.  linkat() will do the same if AT_SYMLINK_FOLLOW
     is set in flags, but it will link on the symlink itself if the flag is
     clear.


RETURN VALUES

     The link() and linkat() functions return the value 0 if successful; oth-
     erwise the value -1 is returned and the global variable errno is set to
     indicate the error.


ERRORS

     link() and linkat() will fail and no link will be created if:

     [EACCES]           A component of either path prefix denies search per-
                        mission, or the requested link requires writing in a
                        directory with a mode that denies write permission.

     [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.

     [EEXIST]           The link named by name2 does exist.

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

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

     [ELOOP]            Too many symbolic links were encountered in translat-
                        ing one of the pathnames.

     [EMLINK]           The link count of the file named by name1 would exceed
                        {LINK_MAX}.

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX} charac-
                        ters, or an entire path name exceeded {PATH_MAX} char-
                        acters.

     [ENOENT]           A component of either path prefix does not exist, or
                        the file named by name1 does not exist.

     [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 direc-
                        tory.

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

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

     [EPERM]            The file named by name1 is a directory and the effec-
                        tive user ID is not super-user, or the file system
                        containing the file does not permit the use of link()
                        on a directory.

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

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

     In addition, linkat() will fail if:

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

     [ENOTDIR]          name1 or name2 is not an absolute path and fd1 or fd2,
                        respectively, is a file descriptor associated with a
                        non-directory file.


SEE ALSO

     symlink(2), unlink(2)


STANDARDS

     The link() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').
     linkat() conforms to IEEE Std 1003.1-2008 (``POSIX.1'').


HISTORY

     The link() function appeared in Version 1 AT&T UNIX.

NetBSD 10.1                    September 1, 2019                   NetBSD 10.1