kill - send a signal to a process

Options you will use

-l, --list

List the signal names.

-TERM, -15

Polite request to shut down. The default. Catchable - the process can clean up.

-KILL, -9

Kernel destroys the process. NOT catchable, no cleanup, no chance to flush.

-HUP, -1

Hang up. Daemons conventionally reload their config on this.

-INT, -2

What Ctrl+C sends.

-STOP, -CONT

Suspend (state T) and resume. STOP is not catchable either.

Gotchas

• kill -9 cannot touch a process in D state: the signal is only delivered when the process returns to userspace, and it never does until the I/O completes.

Taught in

• 1.15 Who's in charge
• 2.10 Restart policy and clean signals
• 3.6 Signals
• 3.8 Zombies, orphans and PID 1
• 5.11 cgroup OOM and exit 137
• 20.3 The JDK tools, and who may attach