ln(1bsd)

ln -- (BSD) make hard or symbolic links to files

Synopsis

   /usr/ucb/ln [-fs] file [linkname]
   
   /usr/ucb/ln [-fs] pathname . . . directory

Description

/usr/ucb/ln creates an additional directory entry, called a link, to a file or directory. Any number of links can be assigned to a file. The number of links does not affect other file attributes such as size, protections, data, and so on.

file is the name of the original file or directory. linkname is the new name to associate with the file or filename. If linkname is omitted, the last component of file is used as the name of the link.

If the last argument is the name of a directory, symbolic links are made in that directory for each pathname argument; /usr/ucb/ln uses the last component of each pathname as the name of each link in the named directory.

A hard link (the default) is a standard directory entry just like the one made when the file was created. Hard links can only be made to existing files. Hard links cannot be made across file systems (disk partitions, mounted file systems). To remove a file, all hard links to it must be removed, including the name by which it was first created; removing the last hard link releases the inode associated with the file.

A symbolic link, made with the -s option, is a special directory entry that points to another named file. Symbolic links can span file systems and point to directories. In fact, you can create a symbolic link that points to a file that is currently absent from the file system; removing the file that it points to does not affect or alter the symbolic link itself.

A symbolic link to a directory behaves differently than you might expect in certain cases. While an /usr/ucb/ls on such a link displays the files in the pointed-to directory, an `/usr/ucb/ls -l' displays information about the link itself:

   example% /usr/ucb/ln -s dir link
   example% /usr/ucb/ls link
   file1 file2 file3 file4
   example% /usr/ucb/ls -l link
   lrwxrwxrwx  1 user            7 Jan 11 23:27 link -> dir

When you cd(1) to a directory through a symbolic link, you wind up in the pointed-to location within the file system. This means that the parent of the new working directory is not the parent of the symbolic link, but rather, the parent of the pointed-to directory. For instance, in the following case the final working directory is /var and not /home/user/linktest.

   example% pwd
   /home/user/linktest
   example% /usr/ucb/ln -s /var/tmp symlink
   example% cd symlink
   example% cd ..
   example% pwd
   /var

C shell user's can avoid any resulting navigation problems by using the pushd and popd built-in commands instead of cd.

Options

-f: Force a hard link to a directory -- this option is only available to the super-user.
-s: Create a symbolic link or links.

Examples

The commands below illustrate the effects of the different forms of the /usr/ucb/ln command:

example% /usr/ucb/ln file link example% /usr/ucb/ls -F file link file link example% /usr/ucb/ln -s file symlink example% /usr/ucb/ls -F file symlink file symlink@ example% /usr/ucb/ls -li file link symlink 10606 -rw-r--r-- 2 user 0 Jan 12 00:06 file 10606 -rw-r--r-- 2 user 0 Jan 12 00:06 link 10607 lrwxrwxrwx 1 user 4 Jan 12 00:06 symlink -> file example% /usr/ucb/ln -s nonesuch devoid example% /usr/ucb/ls -F devoid devoid@ example% cat devoid ux:cat: ERROR: Cannot open devoid: No such file or directory example% /usr/ucb/ln -s /proto/bin/* /tmp/bin example% /usr/ucb/ls -F /proto/bin /tmp/bin /proto/bin: x* y* z*

/tmp/bin: x@ y@ z@

References

cp(1), link(2), ls(1), ls(1bsd), mv(1), readlink(2), rm(1) stat(2), symlink(2)

Notices

When the last argument is a directory, simple basenames should not be used for pathname arguments. If a basename is used, the resulting symbolic link points to itself:

   example% /usr/ucb/ln -s file /tmp
   example% ls -l /tmp/file
   lrwxrwxrwx  1 user    4 Jan 12 00:16 /tmp/file -> file
   example% cat /tmp/file
   ux:cat:ERROR:Cannot open /tmp/file:
   Too many symbolic links in pathname traversal.

To avoid this problem, use full pathnames, or prepend a reference to the PWD variable to files in the working directory:

   example% rm /tmp/file
   example% /usr/ucb/ln -s $PWD/file /tmp
   example% /usr/ucb/ls -l /tmp/file
   lrwxrwxrwx  1 user
       4  Jan 12 00:16 /tmp/file -> /home/user/subdir/file