Signal

Core Idea

A signal is a notification sent to a process to interrupt it, stop it, continue it, terminate it, or report an event.

Signal	Common Trigger	Meaning
`SIGINT`	`Ctrl-C`	Interrupt the foreground process.
`SIGTSTP`	`Ctrl-Z`	Stop the foreground process.
`SIGCONT`	`fg` or `bg`	Continue a stopped process.
`SIGTERM`	`kill PID` default	Ask a process to terminate.
`SIGKILL`	`kill -9 PID`	Force termination; cannot be handled. Use rarely.

sleep 60
# press Ctrl-C

sleep 60
# press Ctrl-Z
jobs
fg

ps -u "$USER" -o pid,comm,args
kill PID

Use ps first. Kill only processes you understand and own.

kill sends a signal; it does not always immediately destroy a process.
Ctrl-C affects the foreground process attached to your terminal.
Ctrl-Z stops a process; it does not end it.
kill -9 skips cleanup. Do not make it your first move.
systemd stopping a service usually sends a termination signal to the service process.

Start sleep 60, stop it with Ctrl-Z, show it with jobs, continue it with fg, then interrupt it with Ctrl-C.