A symbolic link is a special file that usually has a pathname as its data. When the symbolic link is named in an I/O request—by open(), for example—the link portion of the pathname is replaced by the link's "data" and the path is reevaluated.
Symbolic links are a flexible means of pathname indirection and are often used to provide multiple paths to a single file. Unlike hard links, symbolic links can cross filesystems and can also link to directories.
In the following example, the directories /net/node1/usr/fred and /net/node2/usr/barney are linked even though they reside on different filesystems—they're even on different nodes (see the following diagram). You can't do this using hard links, but you can with a symbolic link, as follows:
ln -s /net/node2/usr/barney /net/node1/usr/fred
Note how the symbolic link and the target directory need not share the same name. In most cases, you use a symbolic link for linking one directory to another directory. However, you can also use symbolic links for files, as in this example:
ln -s /net/node1/usr/src/game.c /net/node1/usr/eric/src/sample.c
Figure 1. Symbolic links.Several functions operate directly on the symbolic link. For these functions, the replacement of the symbolic element of the pathname with its target is not performed. These functions include unlink() (which removes the symbolic link), lstat(), and readlink().
Since symbolic links can point to directories, incorrect configurations can result in problems, such as circular directory links. To recover from circular references, the system imposes a limit on the number of hops; this limit is defined as SYMLOOP_MAX in the <limits.h> include file.