Re: Making sure script only runs once instance at a time.

[Hari Sekhon]

Fredrik Lundh wrote: Hari Sekhon wrote: I'm not sure if that is a very old way of doing it, which is why I was reluctant to do it. My way actually uses the process list of the os (linux) and counts the number of instances. If it is more than 0 then another process is running and the script exits gracefully. the code that reliably identifies instances of a given program would be interesting to see. Also, apart from the fact the using lockfiles feels a bit 1970s, I have > found that in real usage of other programs within the company that use > lockfiles, it sometimes causes a bit of troubleshooting time when > it stops working due to a stale lockfile. to minimize that risk, store the pid in the lockfile (and preferrably also the host name), and make sure that the program checks that the pid is still active before it "stops working". </F> How exactly do you check that the pid is still active in python? Is there a library or something that will allow me to manipulate system processes and listings etc the way everybody does in unix shells.... I'm a huge fan of shell so I've done my own thing which leans on shell as follows: import sys,commands,os scriptpath = sys.argv[0] scriptname = os.path.basename(scriptpath) number_procs=commands.getstatusoutput('ps -ef|grep %s|grep -v grep|wc -l' % scriptpath) if number_procs > 1:     print "There appears to be another %s process running." % scriptname     print "Please do not run more than one instance of this program"     print "Quitting for safety..."     sys.exit(200) This works nicely for me. You might also want to add a bit of discrimination to the script (something along the lines of "get a decent os"...since this won't work on windows) import platform if platform.system() != 'Linux':     print "Sorry but this program can only be run on Linux"     sys.exit(201)     #todo: should do a bit extra for our bsd cousins here.... Let me know if you think you have a better way. Please provide a code snippet if so. -h

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