how to detect Linux shutdown/reboot

Question

I\'m trying to detect shut down or reboot from Linux in my c program. I found that program can use signal(SIGTERM, handler) (SIGKILL, handler). But these two will trigger if

Answer 1

Catch SIGTERM. In the handler, read the /var/run/utmp file to get the runlevel. See the source code of the runlevel(8) command for reference.