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POStandard or best practise for unique process identifier (on Unix-like OS)
 

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  1. POStandard or best practise for unique process identifier (on Unix-like OS)
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    <p>On Unix systems PID is unique only at any given point in time. It is not unique in a given time interval because <a href="https://superuser.com/questions/135007/how-are-pids-generated">PIDs used in the past can be re-used</a> after the original process terminates. For storing of history data of all the processes which were running on the system since boot I need identifiers to be unique since the boot.</p> <p>Is there any standard or best practise for that? Is there anything wrong or missing in my intended solution below?</p> <h2>Intended solution</h2> <p>It seems logical to use PID together with the process start time (as standard <a href="http://en.wikipedia.org/wiki/Unix_time" rel="nofollow noreferrer">Unix time</a>) as a unique process identifier. Such identifier would be even unique between reboots.</p> <p><strong>Advantages</strong></p> <ol> <li>Both PID and process start time are clearly defined enough and make sense on all Unix-like systems.</li> <li>Both values are integers and relatively easy to process.</li> <li>Processes can be unambiguously sorted by start time followed by PID.</li> <li>Both values can serve other uses besides of just unique identification of processes.</li> </ol> <p><strong>Disadvantages</strong></p> <ol> <li>There seems to be no portable way of getting the process start time except calling external utility <code>ps</code>. For example in shell: <code>date -d "$(ps -p $PID -o lstart=)" +%s</code>. In Linux it is possible to compute the process start time from <code>/proc/$PID/stat</code> but this method does not work on other systems.</li> <li>Because of the facts in the previous point the portable method can be unnecessarily slow and resource intensive.</li> </ol>
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