[systemd-devel] How are the running processes killed at shutdown?

[tom289332 at Safe-mail.net]

Hello,

How does systemd kill the running processes at shutdown?
(I tried asking at fedoraforum.org first, but got no responses there.)

Presumably it tries to gracefully stop all services. Is every process part of a service?
When it stops a service, it presumably runs the ExecStop of that service, but what if the service doesn't exit immediately? How long does systemd wait? What does it do then?
When is a service considered stopped? I made a service that launches a script that just sleeps. After stopping the service, the script was still running, but the service was considered "inactive (dead)".
What if a service has KillMode=none?
If some processes are not part of any service, when and how are they killed?
Anything else that you consider relevant?

Thanks,
Tom