Softlink - POSIX and Unix-like Operating Systems

POSIX and Unix-like Operating Systems

In POSIX-compliant operating systems, symbolic links are created with the symlink system call. The ln shell command normally uses the link system call, which creates a hard link. When the ln -s flag is specified, the symlink system call is used instead, creating a symbolic link. Symlinks were introduced in 4.2BSD Unix from U.C. Berkeley.

The following command creates a symbolic link at the command-line interface (shell):

ln -s target_path link_path

target_path is the relative or absolute path to which the symbolic link should point. Usually the target will exist, although symbolic links may be created to non-existent targets. link_path is the path of the symbolic link.

After creating the symbolic link, it may generally be treated as an alias for the target. Any file system management commands (e.g., cp, rm) may be used on the symbolic link. Commands which read or write file contents will access the contents of the target file. The rm (delete file) command, however, removes the link itself, not the target file.

The POSIX directory listing application, ls, denotes symbolic links with an arrow after the name, pointing to the name of the target file (see following example), when the long directory list is requested (-l option). When a directory listing of a symbolic link that points to a directory is requested, only the link itself will be displayed. In order to obtain a listing of the linked directory, the path must include a trailing directory separator character ('/', slash).

$ mkdir -p /tmp/one/two $ echo "test_a" >/tmp/one/two/a $ echo "test_b" >/tmp/one/two/b $ cd /tmp/one/two $ ls -l -rw-r--r-- 1 user group 7 Jan 01 10:01 a -rw-r--r-- 1 user group 7 Jan 01 10:01 b $ cd /tmp $ ln -s /tmp/one/two three $ ls -l /tmp/three lrwxrwxrwx 1 user group 12 Jul 22 10:02 /tmp/three -> /tmp/one/two $ ls -l /tmp/three/ -rw-r--r-- 1 user group 7 Jan 01 10:01 a -rw-r--r-- 1 user group 7 Jan 01 10:01 b $ cd three $ ls -l -rw-r--r-- 1 user group 7 Jan 01 10:01 a -rw-r--r-- 1 user group 7 Jan 01 10:01 b $ cat a test_a $ cat /tmp/one/two/a test_a $ echo "test_c" >/tmp/one/two/a $ cat /tmp/one/two/a test_c $ cat /tmp/three/a test_c