Okay, after along time working on Mac, today I opened up one of my old project on a Slackware server. And one of the thing I want to do is connect remotely to the MySQL which is running in Slackware, however it failed to connect.
Thought that I have to do something with my.conf, but NO, the answer stay in /etc/rc.d/rc.mysqld for that you need to comment the following line
and voilà, after restarting mysql, you will get port 3306 is listening for remote connection
Have fun with Slackware!