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diff --git a/doc/s6-svlink.html b/doc/s6-svlink.html new file mode 100644 index 0000000..2e03eec --- /dev/null +++ b/doc/s6-svlink.html @@ -0,0 +1,111 @@ +<html> + <head> + <meta name="viewport" content="width=device-width, initial-scale=1.0" /> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6: the s6-svlink program</title> + <meta name="Description" content="s6: the s6-svlink program" /> + <meta name="Keywords" content="s6 command s6-svlink supervision service start scandir servicedir" /> + <!-- <link rel="stylesheet" type="text/css" href="//skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6</a><br /> +<a href="//skarnet.org/software/">Software</a><br /> +<a href="//skarnet.org/">skarnet.org</a> +</p> + +<h1> The s6-svlink program </h1> + +<p> + <tt>s6-svlink</tt> creates, in a <a href="scandir.html">scan +directory</a>, a symlink to a <a href="servicedir.html">service +directory</a>, and notifies <a href="s6-svscan.html">s6-svscan</a> +that a new service has been registered. It waits until a +<a href="s6-supervise.html">s6-supervise</a> supervisor process has +been spawned to manage the new service, then exits. +</p> + +<p> + The point of <tt>s6-svlink</tt> is to help integrate existing +service directories into an existing service manager sequence and +eliminating race conditions. +</p> + +<h2> Interface </h2> + +<pre> + s6-svlink [ -d | -D ] [ -P ] [ -f ] [ -t <em>timeout</em> ] <em>scandir</em> <em>servicedir</em> [ <em>name</em> ] +</pre> + +<ul> + <li> <tt>s6-svlink</tt> expects a running <a href="s6-svscan.html">s6-svscan</a> +process on <em>scandir</em> and a fully functional, but unsupervised, +<a href="servicedir.html">service directory</a> in <em>servicedir</em>. </li> + <li> It symlinks <em>servicedir</em> into <em>scandir</em>. The symbolic link +is named <em>name</em>; if no <em>name</em> argument has been given, the name given +to the symbolic link is the basename of <em>servicedir</em>. </li> + <li> It sends a command to <a href="s6-svscan.html">s6-svscan</a> to signal it +that a new service is available. </li> + <li> It waits for a <a href="s6-supervise.html">s6-supervise</a> process to be +spawned on <em>servicedir</em>. </li> + <li> It exits 0. </li> +</ul> + +<h2> Exit codes </h2> + +<ul> + <li> 0: success </li> + <li> 99: timeout while waiting for the supervisor to start </li> + <li> 100: wrong usage </li> + <li> 111: system call failed </li> +</ul> + +<h2> Options </h2> + +<ul> + <li> <tt>-d</tt> : down. The supervisor will be started, but the service +itself will remain down. Any <em>servicedir</em><tt>/down</tt> file will be +deleted. By default, if neither the <tt>-d</tt> nor <tt>-D</tt> options have +been given, the supervisor auto-starts the service as soon as it runs. </li> + <li> <tt>-D</tt> : down, and stay down. The supervisor will be started, +but the service itself will remain down. A <em>servicedir</em><tt>/down</tt> file +will be created. By default, if neither the <tt>-d</tt> nor <tt>-D</tt> options have +been given, the supervisor auto-starts the service as soon as it runs. </li> + <li> <tt>-P</tt> : public. If <em>servicedir</em><tt>/event</tt> does not +exist, it will be created as public, i.e. anyone will be able to subscribe to +this <a href="fifodir.html">fifodir</a>. By default, it will be created as private, +i.e. only processes running with the same gid as the <a href="s6-svscan.html">s6-svscan</a> +process will be able to susbscribe to it. </li> + <li> <tt>-f</tt> : force permissions. The presence or absence of the <tt>-P</tt> +option (i.e. the public or private state of <em>servicedir</em><tt>/event</tt>) will be +enforced even if <em>servicedir</em><tt>/event</tt> already exists. By default, +<tt>s6-svlink</tt> exits with an error message if <em>servicedir</em><tt>/event</tt> +exists and its public/private state mismatches what is requested. </li> + <li> <tt>-t <em>timeout</em></tt> : if the supervisor has not started +after <em>timeout</em> milliseconds, <tt>s6-svlink</tt> will print a message +to stderr and exit 99. By default, <em>timeout</em> is 0, which means no time +limit. </li> +</ul> + +<h2> Notes </h2> + +<ul> + <li> Using <tt>s6-svlink</tt> to start services is a suboptimal pattern: it +requires precise manipulations involving use of <a href="s6-ftrigrd.html">s6-ftrigrd</a> +in order to avoid race conditions, so it is relatively expensive. The simpler, +more efficient pattern is to have all the supervisors already started at boot +time, so the existence of the supervisor can be relied on, and starting the +service becomes a trival and instant operation - this is, for instance, how +the <a href="//skarnet.org/software/s6-rc/">s6-rc</a> service manager behaves. +However, it can be difficult to implement this pattern with other services +managers such as OpenRC; in those cases, <tt>s6-svlink</tt>, which starts the +supervisors one at a time, can be used instead. </li> + <li> If <em>servicedir</em> is logged, i.e. <em>servicedir</em><tt>/log</tt> +is also a valid service directory, then <tt>s6-svlink</tt> will wait until +supervisors have been spawned for both the service and its logger. </li> +</ul> + +</body> +</html> |