- make hard or symbolic links to files
/usr/ucb/ln [-fs] filename [linkname]
/usr/ucb/ln [-fs] pathname... directory
The /usr/ucb/ln utility 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, etc.
filename 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 filename 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 ls(1) on such a link displays the files in the pointed-to directory, an `ls -l' displays information about the link itself:
example% /usr/ucb/ln -s dir link example% ls link file1 file2 file3 file4 example% ls -l link lrwxrwxrwx 1 user 7 Jan 11 23:27 link -> dir
When you use cd(1) to change 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 /usr 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 /usr
C shell user's can avoid any resulting navigation problems by using the pushd and popd built-in commands instead of cd.
Force a hard link to a directory. This option is only available to the super-user, and should be used with extreme caution.
Create a symbolic link or links.
See largefile(5) for the description of the behavior of ln when encountering files greater than or equal to 2 Gbyte ( 231 bytes).
示例 1 The /usr/ucb/ln command
The commands below illustrate the effects of the different forms of the /usr/ucb/ln command:
example% /usr/ucb/ln file link example% ls -F file link file link example% /usr/ucb/ln -s file symlink example% ls -F file symlink file symlink@ example% 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% ls -F devoid devoid@ example% cat devoid devoid: No such file or directory example% /usr/ucb/ln -s /proto/bin/* /tmp/bin example% ls -F /proto/bin /tmp/bin /proto/bin: x* y* z* /tmp/bin: x@ y@ z@
See attributes(5) for descriptions of the following attributes:
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 /tmp/file: Too many levels of symbolic links
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 lrwxrwxrwx 1 user 4 Jan 12 00:16 /tmp/file -> /home/user/subdir/file