Beefy Boxes and Bandwidth Generously Provided by pair Networks
P is for Practical
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

PID files have a "fun" gotcha in daemons started as part of system boot — two instances of the same daemon may well get the same PID!

This does not prevent using a PID file, after all, you know that this instance of the program has not written the PID file yet, so if you read it and find that it matches $$, you know the PID has been recycled across reboots.

Perhaps the best option would be to place the PID file on a RAM filesystem that starts out empty every time the system boots. This way, there is no possibility of a stale PID file from the previous session and you avoid needless flash writes as a bonus.

Even if the daemon is run from cron, this issue could bite our questioner — the daemon reboots the system if the time is not set within some grace period, so a network failure could cause the system to start, fail to set the clock, reboot, start the daemon with the same PID again, fail to set the clock, ...


In reply to Re^2: Preventing multiple instances by jcb
in thread Preventing multiple instances by Bod

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others having an uproarious good time at the Monastery: (3)
    As of 2021-05-08 13:44 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?
      Perl 7 will be out ...





      Results (96 votes). Check out past polls.

      Notices?