Why does this 'kill' command log me out of the computer?

The following command signs me out (do not run this command):

kill -9 -1

I don't understand why.

Can someone explain this to me?

The syntax is kill SIGNAL PID.

The -9 option specifies that the SIGKILL signal should be sent (immediately terminate the target process(es), and specifying the PID -1 is shorthand for "all processes except itself and init".

Since you don't use sudo (and presumably don't have root permissions), this immediately kills all processes you have permission to kill - your entire session, hence logging you out.

try

man kill

to get an explanation of the kill command..

it says:

A PID of -1 is special; it indicates all processes except the kill process itself and init.

and

EXAMPLES

kill -9 -1

 Kill all processes you can kill.

I hope you understand why your computer will log you out, when you end all processes. You quitted everything.

Hope this helps.

You are giving -1 as the process id: from the kill man-page:

 A  PID of -1 is special; it indicates all processes except the
 kill process itself and init.