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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2014-09-19 15:01:58 +0000 |
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| committer | Laurent Bercot <ska-skaware@skarnet.org> | 2014-09-19 15:01:58 +0000 |
| commit | 54b6467013bfbdb3ee606961c02fbff1271ca582 (patch) | |
| tree | e3969743e61542979f12fca01017e67c4480eca8 /doc/s6-devd.html | |
| download | s6-linux-utils-54b6467013bfbdb3ee606961c02fbff1271ca582.tar.xz | |
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diff --git a/doc/s6-devd.html b/doc/s6-devd.html new file mode 100644 index 0000000..5ae6160 --- /dev/null +++ b/doc/s6-devd.html @@ -0,0 +1,80 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6-linux-utils: the s6-devd program</title> + <meta name="Description" content="s6-linux-utils: the s6-devd program" /> + <meta name="Keywords" content="s6 linux administration root utilities devd mdev udev" /> + <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6-linux-utils</a><br /> +<a href="http://skarnet.org/software/">Software</a><br /> +<a href="http://skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>s6-devd</tt> program </h1> + +<p> +<tt>s6-devd</tt> listens to the netlink interface for udev events, and +launches a helper program for every event, similarly to what the hotplug +interface does. +</p> + +<h2> Interface </h2> + +<pre> + s6-devd [ -q | -v ] [ -b kbufsz ] [ -t l:t:k ] <em>prog...</em> +</pre> + +<ul> + <li> s6-devd binds to the netlink interface and listens for +hotplug events, as the <em>udev</em> program does. </li> + <li> For every event it receives, it spawns <em>prog...</em> with +the event variables added to the environment, just as if <em>prog...</em> +had been registered in <tt>/proc/sys/kernel/hotplug</tt>. </li> + <li> However, unlike the kernel, s6-devd spawns the <em>prog...</em> helpers +sequentially: it waits for an instance to finish before spawning another one. </li> + <li> s6-devd is a long-lived program; it exits 0 when it receives a +SIGTERM. If a helper program is alive at that time, s6-devd waits for it to die +before exiting. </li> +</ul> + +<h2> Options </h2> + +<ul> + <li> <tt>-q</tt> : be more quiet. </li> + <li> <tt>-v</tt> : be more verbose. </li> + <li> <tt>-b</tt> <em>kbufsz</em> : try and reserve a kernel buffer of +<em>kbufsz</em> bytes for the netlink queue. Too large a buffer wastes kernel memory; +too small a buffer risks losing events. The default is 65536. </li> + <li> <tt>-t</tt> <em>l:t:k</em> : If <em>l</em>, <em>t</em> or <em>k</em> is +specified, they specify timeouts; by default, they are infinite. +If <em>prog...</em> is still alive after <em>l</em> milliseconds, s6-devd sends +it a SIGTERM. Then, if <em>prog...</em> is still alive after <em>t</em> more +milliseconds, s6-devd sends it a SIGKILL. Then, if <em>prog...</em> is still +alive after <em>k</em> more milliseconds, s6-devd yells and exits 99. </li> +</ul> + +<h2> Notes </h2> + +<ul> + <li> s6-devd is a daemon; it should be run under a proper supervision system such +as <a href="http://skarnet.org/software/s6/">s6</a>. (That is why it does not +fork and logs to stderr.) </li> + <li> The <em>prog...</em> helper, on the other hand, should be very short-lived, +even if you are not using the <tt>-t</tt> option to s6-devd. Since helpers are +spawned sequentially, slow helpers can make events queue up and fill the netlink +kernel buffer. </li> + <li> If you are using <a href="http://busybox.net/">busybox</a> and want a +minimal udev-style dynamic <tt>/dev</tt> +handling, <tt>/sbin/mdev</tt> is a suitable <em>prog...</em> helper. </li> + <li> The point of s6-devd is that it runs the helpers sequentially, so it solves +the race condition that appears when helpers are run via the hotplug interface. +When s6-devd is used, <tt>/proc/sys/kernel/hotplug</tt> should be empty. </li> +</ul> + +</body> +</html> |