Linux 中ln 命令-n 参数的含义
参考：
https://superuser.com/questions/645842/how-to-overwrite-a-symbolic-link-of-a-directory
参考的文章中已经说的很清楚了，我稍微补充一下，引用原帖的例子
The proper way to do this is to use the -n, --no-dereference option like so.
$ ln -snf foo2 bar
This causes ln to treat the existing symlink as a file. Otherwise, it dereferences bar to foo1, descends into foo1 and uses the original TARGET name as the LINK_NAME and that's why you end up with a symlink to foo2 being created inside the foo1 directory. The manpage on ln states the following...
-n, --no-dereference
treat LINK_NAME as a normal file if it is a symbolic link to a
directory
Below is the shell output on my Arch Linux desktop with version 8.21 of ln with and without the --no-dereference option, I got the same results you did without the --no-dereference option, but using the --no-dereference option it worked as expected.
$ mkdir foo1 foo2
$ ln -s foo1 bar
$ ls -l bar
lrwxrwxrwx 1 drew users 4 Sep 17 12:51 bar -> foo1
$ ln -sf foo2 bar
$ ls -l bar
lrwxrwxrwx 1 drew users 4 Sep 17 12:51 bar -> foo1
$ ls -l foo1
total 0
lrwxrwxrwx 1 drew users 4 Sep 17 12:51 foo2 -> foo2
$ ln -snf foo2 bar
$ ls -l bar
lrwxrwxrwx 1 drew users 4 Sep 17 12:52 bar -> foo2简单来说-n 就是让已存在的符号链接(即软连接)不被转义解析，就相当于$var 原样输出而不是取其被赋予的值。
man ln 显示了创建link 的四种方式
NAME
ln - make links between files
SYNOPSIS
ln [OPTION]... [-T] TARGET LINK_NAME (1st form)
ln [OPTION]... TARGET (2nd form)
ln [OPTION]... TARGET... DIRECTORY (3rd form)
ln [OPTION]... -t DIRECTORY TARGET... (4th form)
DESCRIPTION
In the 1st form, create a link to TARGET with the name LINK_NAME. In the 2nd
form, create a link to TARGET in the current directory. In the 3rd and 4th forms,
create links to each TARGET in DIRECTORY. Create hard links by default, symbolic
links with --symbolic. By default, each destination (name of new link) should not
already exist. When creating hard links, each TARGET must exist. Symbolic links
can hold arbitrary text; if later resolved, a relative link is interpreted in
relation to its parent directory.
Mandatory arguments to long options are mandatory for short options too.
如果恰巧相被覆盖的软连接指向的是一个目录的话，不加-n 参数，则相当于第二种创建方法，即在某目录下创建软连接文件。