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diff --git a/.html/devops/self-daemonization-sucks.html b/.html/devops/self-daemonization-sucks.html deleted file mode 100644 index 14e2c01..0000000 --- a/.html/devops/self-daemonization-sucks.html +++ /dev/null @@ -1,162 +0,0 @@ -<!DOCTYPE html> -<html> -<head> - <title> - The Codex » - Self-daemonizing code is awful - </title> - - <link - rel='stylesheet' - type='text/css' - href='http://fonts.googleapis.com/css?family=Buenard:400,700&subset=latin,latin-ext'> - <link - rel="stylesheet" - type="text/css" - href="../media/css/reset.css"> - <link - rel="stylesheet" - type="text/css" - href="../media/css/grimoire.css"> -</head> -<body> - -<div id="shell"> - - <ol id="breadcrumbs"> - - <li class="crumb-0 not-last"> - - <a href="../">index</a> - - </li> - - <li class="crumb-1 not-last"> - - <a href="./">devops</a> - - </li> - - <li class="crumb-2 last"> - - self-daemonization-sucks - - </li> - - </ol> - - - - <div id="article"> - <h1 id="self-daemonizing-code-is-awful">Self-daemonizing code is awful</h1> -<p>The classical UNIX approach to services is to implement them as “daemons,” -programs that run without a terminal attached and provide some service. The -key feature of a classical daemon is that, when started, it carefully -detaches itself from its initial environment and terminal, then continues -running in the background.</p> -<p>This is awful and I'm glad modern init replacements discourage it.</p> -<h2 id="process-tracking">Process Tracking</h2> -<p>Daemons don't exist in a vacuum. Administrators and owners need to be able to -start and stop daemons reliably, and check their status. The classic -self-daemonization approach makes this impossible.</p> -<p>Traditionally, daemons run as children of <code>init</code> (pid 1), even if they start -out as children of some terminal or startup process. Posix only provides -deterministic APIs for processes to manage their children and their immediate -parents; the classic daemonisation protocol hands the newly-started daemon -process off from its original parent process, which knows how to start and -stop it, to an unsuspecting <code>init</code>, which has no idea how this specific -daemon is special.</p> -<p>The standard workaround has daemons write their own PIDs to a file, but a -file is “dead” data: it's not automatically updated if the daemon dies, and -can linger long enough to contain the PID of some later, unrelated program. -PID file validity checks generally suffer from subtle (or, sometimes, quite -gross) race conditions.</p> -<h2 id="complexity">Complexity</h2> -<p>The actual <em>code</em> to correctly daemonize a process is surprisingly complex, -given the individual interfaces' relative simplicity:</p> -<ul> -<li> -<p>The daemon must start its own process group</p> -</li> -<li> -<p>The daemon must detach from its controlling terminal</p> -</li> -<li> -<p>The daemon should close (and may reopen) file handles inherited from its - parent process (generally, a shell)</p> -</li> -<li> -<p>The daemon should ensure its working directory is predictable and - controllable</p> -</li> -<li> -<p>The daemon should ensure its umask is predictable and controllable</p> -</li> -<li> -<p>If the daemon uses privileged resources (such as low-numbered ports), it - should carefully manage its effective, real, and session UID and GIDs</p> -</li> -<li> -<p>Daemons must ensure that all of the above steps happen in signal-safe ways, - so that a daemon can be shut down sanely even if it's still starting up</p> -</li> -</ul> -<p>See <a href="http://www.freedesktop.org/software/systemd/man/daemon.html">this list</a> -for a longer version. It's worse than you think.</p> -<p>All of this gets even more complicated if the daemon has its own child -processes, a pattern common to network services. Naturally, a lot of daemons -in the real world get some of these steps wrong.</p> -<h2 id="the-future">The Future</h2> -<p><a href="http://supervisord.org">Supervisord</a>, -<a href="http://ddollar.github.io/foreman/">Foreman</a>, -<a href="http://upstart.ubuntu.com">Upstart</a>, -<a href="https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/launchctl.1.html">Launchd</a>, -<a href="http://www.freedesktop.org/wiki/Software/systemd/">systemd</a>, and <a href="http://cr.yp.to/daemontools.html">daemontools</a> all -encourage services <em>not</em> to self-daemonize by providing a sane system for -starting the daemon with the right parent process and the right environment -in the first place.</p> -<p>This is a great application of -<a href="http://c2.com/cgi/wiki?DontRepeatYourself">DRY</a>, as the daemon management -code only needs to be written once (in the daemon-managing daemon) rather -than many times over (in each individual daemon). It also makes daemon -execution more predictable, since daemons “in production” behave more like -they do when run attached to a developer's console during debugging or -development.</p> - </div> - - - -<div id="comments"> -<div id="disqus_thread"></div> -<script type="text/javascript"> - /* * * CONFIGURATION VARIABLES: EDIT BEFORE PASTING INTO YOUR WEBPAGE * * */ - var disqus_shortname = 'grimoire'; // required: replace example with your forum shortname - - /* * * DON'T EDIT BELOW THIS LINE * * */ - (function() { - var dsq = document.createElement('script'); dsq.type = 'text/javascript'; dsq.async = true; - dsq.src = 'http://' + disqus_shortname + '.disqus.com/embed.js'; - (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(dsq); - })(); -</script> -<noscript>Please enable JavaScript to view the <a href="http://disqus.com/?ref_noscript">comments powered by Disqus.</a></noscript> -<a href="http://disqus.com" class="dsq-brlink">comments powered by <span class="logo-disqus">Disqus</span></a> -</div> - - - - <div id="footer"> - <p> - - The Codex — - - Powered by <a href="http://markdoc.org/">Markdoc</a>. - -<a href="https://bitbucket.org/ojacobson/grimoire.ca/src/master/wiki/devops/self-daemonization-sucks.md">See this page on Bitbucket</a> (<a href="https://bitbucket.org/ojacobson/grimoire.ca/history-node/master/wiki/devops/self-daemonization-sucks.md">history</a>). - - </p> - </div> - -</div> -</body> -</html>
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