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Given PID, make sure a process is running on Unix?

Michael Hudson mwh at python.net
Mon Jul 8 07:05:55 EDT 2002 
pinard at iro.umontreal.ca (François Pinard) writes:

> [VanL]
> 
> > I am trying to get write a python script that on Unix reads a PID from
> > a file and, if that process is still running, exits.  If the process is
> > not running, the process would be started.  [...] Any help?
> 
> You could work along the lines of:
> 
>     try:
>         os.kill(PID, 0)
>     except OSError:
>         print PID, 'is not running'
>     else:
>         print PID, 'is running'
> 
> Killing a process with signal 0 never kills it. :-)

You might want to check why the kill failed -- if the process exists
but is owned by another user (and you're not root), then you get an
OSError, but with a different errno.

     try:
         os.kill(PID, 0)
     except OSError, err:
         if err.err == errno.EPERM:
             print PID, 'is running'
         else:
             print PID, 'is not running'
     else:
         print PID, 'is running'

Whether this distinction matters is something I can't predict from
here.

Cheers,
M.

-- 
  Structure is _nothing_ if it is all you got.  Skeletons _spook_
  people if they try to walk around on their own.  I really wonder 
  why XML does not.                     -- Erik Naggum, comp.lang.lisp
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