How to kill used port of docker

To expand on Robert Moskal's answer, you'll need to kill whatever's already on that port:

• kill all the containers again
• if you're on Linux, kill the process running on your port with fuser -k 9042/tcp
• if above steps don't work, reboot your computer and try again.

Happy hunting!

I used with sudo. it worked me.

sudo fuser -k 9042/tcp

I check port status:

$ netstat -pna | grep 9042
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)