Stopping Processes: kill

Sometimes a process misbehaves: it freezes, consumes all the CPU, or simply needs to be stopped. The kill command sends a signal to a process, asking (or forcing) it to terminate.

The basic usage is: kill PID.

kill 510

This sends signal 15 (SIGTERM), a polite "please shut down." Most well-behaved programs will clean up and exit.

Forcing a stubborn process

If a process ignores SIGTERM, send signal 9 (SIGKILL), an immediate, unconditional termination:

kill -9 510

The process gets no chance to clean up; the kernel destroys it instantly. Use -9 only when the polite signal fails.

Background jobs with &

You can start a process in the background by appending &:

sleep 300 &

[1] 1312

The shell gives you its PID (1312) so you can kill it later if needed.

Mission: Terminate the Frozen Nav-Computer

The navigation computer (PID 510) has locked up mid-calculation and is no longer responding. The pilot needs it gone and an incident record filed.

1. Forcefully terminate the frozen navigation computer (PID 510).
2. Save a fresh snapshot of all still-running processes into a file called after-kill.txt.
3. Create a folder called incident-log and move after-kill.txt into it.
4. Count how many times nav-computer still appears in the saved snapshot.

Expected result

incident-log/after-kill.txt no longer lists the nav-computer process (the count is 0).