How can I find out if a process is still running?
The kill command is used to send signals to a running process. As a convenience function, the signal "0", which does not exist, can be used to find out if a process is still running:
myprog & # Start program in the background daemonpid=$! # ...and save its process id while sleep 60 do if kill -0 $daemonpid # Is the process still alive? then echo >&2 "OK - process is still running" else echo >&2 "ERROR - process $daemonpid is no longer running!" break fi done
This is one of those questions that usually masks a much deeper issue. It's rare that someone wants to know whether a process is still running simply to display a red or green light to an operator. More often, there's some ulterior motive, such as the desire to ensure that some daemon which is known to crash frequently is still running, or to ensure mutually exclusive access to a resource, etc. For much better discussion of these issues, see ProcessManagement or [:BashFAQ#faq33:FAQ #33].