`ln` maybe non-idempotent

```
[root@epsilon:~]# rm -v -f /var/lib/nginx/mywebsql/logs -r
removed ‘/var/lib/nginx/mywebsql/logs’

[root@epsilon:~]# ln -svf /var/log/nginx/mywebsql /var/lib/nginx/mywebsql/logs
‘/var/lib/nginx/mywebsql/logs’ -> ‘/var/log/nginx/mywebsql’

[root@epsilon:~]# ln -svf /var/log/nginx/mywebsql /var/lib/nginx/mywebsql/logs
‘/var/lib/nginx/mywebsql/logs/mywebsql’ -> ‘/var/log/nginx/mywebsql’
```

With the `-T` option:
```
[root@epsilon:~]# rm -v -f /var/lib/nginx/mywebsql/logs -r

[root@epsilon:~]# ln -Tsvf /var/log/nginx/mywebsql /var/lib/nginx/mywebsql/logs
‘/var/lib/nginx/mywebsql/logs’ -> ‘/var/log/nginx/mywebsql’

[root@epsilon:~]# ln -Tsvf /var/log/nginx/mywebsql /var/lib/nginx/mywebsql/logs
‘/var/lib/nginx/mywebsql/logs’ -> ‘/var/log/nginx/mywebsql’

[root@epsilon:~]# ln -Tsvf /var/log/nginx/mywebsql /var/lib/nginx/mywebsql/logs
‘/var/lib/nginx/mywebsql/logs’ -> ‘/var/log/nginx/mywebsql’
```