LN(1) BSD Reference Manual LN(1)
ln - make hard and symbolic links to files
ln [-fhns] source_file [target_file] ln [-fs] source_file ... [target_dir]
The ln utility creates a new directory entry (linked file) which has the same modes as the original file. It is useful for maintaining multiple copies of a file in many places at once without using up storage for the copies; instead, a link "points" to the original copy. There are two types of links; hard links and symbolic links. How a link points to a file is one of the differences between a hard and symbolic link. The options are as follows: -f Unlink any already existing file, permitting the link to occur. -h If the target is a symlink to a directory, do not descend into it. -n An alias for -h for compatibility with other operating systems. -s Create a symbolic link. By default, ln makes "hard" links. A hard link to a file is indistin- guishable from the original directory entry; any changes to a file are effectively independent of the name used to reference the file. Hard links may not normally refer to directories and may not span file sys- tems. A symbolic link contains the name of the file to which it is linked. The referenced file is used when an open(2) operation is performed on the link. A stat(2) on a symbolic link will return the linked-to file; an lstat(2) must be done to obtain information about the link. The readlink(2) call may be used to read the contents of a symbolic link. Symbolic links may span file systems, refer to directories, and refer to non-existent files. Given one or two arguments, ln creates a link to an existing file source_file. If target_file is given, the link has that name; target_file may also be a directory in which to place the link. Otherwise, it is placed in the current directory. If only the directory is specified, the link will be made to the last component of source_file. Given more than two arguments, ln makes links in target_dir to all the named source files. The links made will have the same name as the files being linked to. The ln utility exits 0 on success or >0 if an error occurred.
Create a symbolic link named /home/www and point it to /var/www: # ln -s /var/www /home/www Hard link /usr/local/bin/fooprog to file /usr/local/bin/fooprog-1.0: # ln /usr/local/bin/fooprog-1.0 /usr/local/bin/fooprog As an exercise, try the following commands: $ ls -i /bin/[ 11553 /bin/[ $ ls -i /bin/test 11553 /bin/test Note that both files have the same inode; that is, /bin/[ is essentially an alias for the test(1) command. This hard link exists so test(1) may be invoked from shell scripts, for example, using the if [ ] construct. In the next example, the second call to ln removes the original foo and creates a replacement pointing to baz: $ mkdir bar baz $ ln -s bar foo $ ln -shf baz foo Without the -h option, this would instead leave foo pointing to bar and inside foo create a new symlink baz pointing to itself. This results from directory-walking.
link(2), lstat(2), readlink(2), stat(2), symlink(2), symlink(7)
An ln utility appeared in Version 3 AT&T UNIX.
Since the source_file must have its link count incremented, a hard link cannot be created to a file which is flagged immutable or append-only (see chflags(1)). MirOS BSD #10-current December 30, 1993 1
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