How to terminate current colab session from notebook cell

We have a way to do this correctly now:

from google.colab import runtime
runtime.unassign()

A rather ugly but efficient solution might be

!kill $(ps aux | awk '{print $2}')

ps aux will give you a list of any process running in the machine, awk '{print $2}' will extract the PID of every process currently running and finally kill will stop them, sending a SIGTERM signal.

This will give you a message "Runtime disconnected" and the session will be closed, you can see it worked under "Runtime" > "Manage sessions".

You can see the available system aliases here