Making sure script only runs once instance at a time.

[Stephan Kuhagen]

Hari Sekhon wrote:

> I have written a script and I would like to ensure that the script is
> never run more than once at any given time.
> 
> What is the best way of testing and exiting if there is another version
> of this script running somewhere on this machine?
> 
> I guess what I'm asking is how to handle system processes the way I can
> in shell. I am running this on linux.

Although the other solution suggested seems to be more general (I have not
read the code, only the info in the header), the following may be
sufficient for what you want, and can be used as code inside of your
script. It searches /proc/ for another process that is a script interpreted
by python and has the same name as your script. So it can fail, if there is
another python script running with the same name, but which is not
identical to your script. OTOH it's a very short and simple test:

-----
#!/bin/env python

import os.path
import linecache

pid=os.getpid()
script=linecache.getline(os.path.join('/proc', str(pid), 'cmdline'),
1).split('\0')[0:2]
for pid in filter(lambda x: x.isdigit() and x != str(pid),
os.listdir('/proc')):
  other=linecache.getline(os.path.join('/proc', str(pid), 'cmdline'),
1).split('\0')[0:2]
  if script[0] == other[0] and os.path.basename(script[-1]) ==
os.path.basename(other[-1]):
    raise "already running!"
-----

HTH
Stephan