Could not bind to 127.0.0.1:9050: Address already in use. Is Tor already running?

What works for me:

killall tor

netstat will tell you what's listening on that port. Open a terminal (press Ctrl+Alt+T), and run:

sudo netstat -plnt | fgrep 9050

It will tell you which program is using that port. For example, on my system, it shows:

tcp       0     0 127.0.0.1:9050         0.0.0.0:*              LISTEN     1198/tor

At the end, it says that the program listening on that port is tor.

@David Foerster's answer: killall tor did not work for me.
I got the result tor: no process found.

New solution: sudo killall tor

restart your device and run again. port will be realse.