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    <p>Since you're using linux, you can make use of <a href="http://docs.python.org/2/library/fcntl.html#fcntl.flock" rel="nofollow"><code>flock</code></a>:</p> <pre class="lang-py prettyprint-override"><code>import os import fcntl import time def main(): # acquire the prog lock if not prog_lock_acq('singleton.lock'): print("another instance is running") exit(1) print("program is running-press Ctrl+C to stop") while True: time.sleep(10) def prog_lock_acq(lpath): fd = None try: fd = os.open(lpath, os.O_CREAT) fcntl.flock(fd, fcntl.LOCK_NB | fcntl.LOCK_EX) return True except (OSError, IOError): if fd: os.close(fd) return False if __name__ == '__main__': main() </code></pre> <p>It doesn't matter that we left the file open after exiting the <code>prog_lock_acq</code> because when the process exits, it will be automatically closed by the OS. Also, if you leave out <code>LOCK_NB</code> option, the <code>flock</code> call will block until the current running process quits. Depending on your use case, that might be useful.</p> <p>Note that we're not deleting the file on exit. It doesn't matter. Existence of the file doesn't indicate a live process—the lock does. So even if you kill your process with <code>kill -9</code>, the lock is still released.</p> <p>There is however a caveat: if you unlink the lock file while the process is running, when the next instance of the process is run, it will create a new file which will have no lock on it and will run just fine which will violate our singleton design. You might be able to do something clever with a directory to prevent unlinking but I'm not sure how robust that would be.</p>
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