Diff for "BashFAQ/042"

Differences between revisions 1 and 2

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].

-  ⇤ ← Revision 1 as of 2007-05-02 23:32:30 → 
  Size: 1135
  Editor: redondos
  Comment:
+   ← Revision 2 as of 2007-11-30 03:02:35 → ⇥
  Size: 1143
  Editor: GreyCat
  Comment: change internal link
-Deletions are marked like this.
+Additions are marked like this.
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-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 [#faq33 FAQ #33].
+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].