If pid is 0, sig shall be sent to all processes (excluding an unspecified set of system processes) whose process group ID is equal to the process group ID of the sender, and for which the process has permission to send a signal
for which the process has permission to send a signal exactly mean?
How can I check which processes will receive a signal?
kill -9 0 kills every process that was started in the current tty and the tty itself. Or is there something else?