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diff --git a/doc/s6-linux-init.html b/doc/s6-linux-init.html new file mode 100644 index 0000000..a4bb636 --- /dev/null +++ b/doc/s6-linux-init.html @@ -0,0 +1,154 @@ +<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-linux-init: the s6-linux-init program</title> + <meta name="Description" content="s6-linux-init: the s6-linux-init program" /> + <meta name="Keywords" content="s6 linux init administration root init boot pid1 pid 1 /sbin/init" /> + <!-- <link rel="stylesheet" type="text/css" href="//skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6-linux-init</a><br /> +<a href="//skarnet.org/software/">Software</a><br /> +<a href="//skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>s6-linux-init</tt> program </h1> + +<p> +<tt>s6-linux-init</tt> is a program that is meant to run as pid 1, +as a <em>stage 1 init</em>: it performs the necessary early system preparation +and execs into <a href="//skarnet.org/software/s6/s6-svscan.html">s6-svscan</a>. +</p> + +<h2> Interface </h2> + +<pre> + s6-linux-init [ -c <em>basedir</em> ] [ -p <em>initial_path</em> ] [ -s <em>env_store</em> ] [ -m <em>umask</em> ] [ -d <em>dev_style</em> ] [ -D <em>initdefault</em> ] [ <em>args...</em> ] +</pre> + +<ul> + <li> If <tt>s6-linux-init</tt> isn't pid 1, it execs into +<a href="s6-linux-init-telinit.html">s6-linux-init-telinit</a> with the +same arguments. </li> + </li> + <li> Else, it performs some early preparation, spawns a process that +will run the <em>rc.init</em> script, then execs into +<a href="//skarnet.org/software/s6/s6-svscan.html">s6-svscan</a>. +</ul> + +<h2> Options </h2> + +<p> + These options should exactly mirror the options with the same name that +have been given to <a href="s6-linux-init-maker.html">s6-linux-init-maker</a>. +If there is a discrepancy, the system might not boot. +</p> + +<ul> + <li> <tt>-c</tt> <em>basedir</em> : read all its initialization +data from <em>basedir</em>. If the data has not indeed been copied to +<em>basedir</em>, <strong>the system will not boot</strong>. </li> + <li> <tt>-p</tt> <em>initial_path</em> : the value to +set the initial PATH environment variable to. + <li> <tt>-s</tt> <em>env_store</em> : the place where to dump +kernel environment variables. </li> + <li> <tt>-m</tt> <em>initial_umask</em> : the value of +the initial file umask. </li> + <li> <tt>-d</tt> <em>dev_style</em> : how <tt>/dev</tt> is +handled on this system. 0 means a static <tt>/dev</tt>, 1 means +devtmpfs but not automounted by the kernel at boot time, and 2 means +devtmpfs automounted by the kernel at boot time. </li> + <li> <tt>-D</tt> <em>initdefault</em> : the initial runlevel +to boot to, if it isn't overridden by the kernel command line. +This is only given as a first argument to <em>rc.init</em>. +Default is <tt>default</tt>. </li> +</ul> + +<h2> Early preparation </h2> + +<p> + When booting a system, <tt>s6-linux-init</tt> performs the following +operations: +</p> + +<ul> + <li> It prints a banner to <tt>/dev/console</tt>. </li> + <li> It chdirs to <tt>/</tt>. </li> + <li> It sets the umask to <em>initial_umask</em>. </li> + <li> It becomes a session leader. </li> + <li> It mounts a devtmpfs on <tt>/dev</tt>, if necessary. </li> + <li> It uses <tt>/dev/null</tt> as its stdin (instead of <tt>/dev/console</tt>). +<tt>/dev/console</tt> is still used, for now, as stdout and stderr. </li> + <li> It unmounts <tt>/run</tt> (or the directory you have given to the +<tt>--tmpfsdir</tt> configure option at package build time), just in case. </li> + <li> It creates a tmpfs on <tt>/run</tt> (or your chosen <em>tmpfsdir</em>). </li> + <li> It copies the whole <tt><em>basedir</em>/run-image</tt> hierarchy to +<tt>/run</tt> (or your chosen tmpfsdir). </li> + <li> It reads the initial environment from <tt><em>basedir</em>/env</tt>. </li> + <li> If required, it stores the kernel environment into <em>env_store</em>. </li> + <li> It performs "the fifo trick", i.e. it redirects its stdout to the +catch-all logger's fifo, without blocking, before the catch-all +logger is even up (because it's a service that will be spawned a bit +later, when <a href="//skarnet.org/software/s6/s6-svscan.html">s6-svscan</a> +is executed). </li> + <li> It forks a child. + <ul> + <li> The child scans the kernel command line to find a suitable runlevel +(<tt>default</tt>, <tt>2</tt>, <tt>3</tt>, <tt>4</tt>, or <tt>5</tt>). If +it doesn't find any kernel command line argument that defines a runlevel, +it uses <em>initdefault</em>. </li> + <li> The child becomes a session leader. </li> + <li> The child blocks until the catch-all logger runs. </li> + </ul> </li> + <li> It also makes the catch-all logger's fifo its stderr. </li> + <li> It execs into <a href="//skarnet.org/software/s6/s6-svscan.html">s6-svscan</a> +with <tt>/run/service</tt> as its scandir (or <em>tmpfsdir</em>/service) </li>. + <ul> + <li> <a href="//skarnet.org/software/s6/s6-svscan.html">s6-svscan</a> +spawns the early services that are defined in +<tt><em>basedir</em>/run-image/service</tt>, and have been copied into +<tt>/run/service</tt> (or <em>tmpfsdir</em>/service). </li> + <li> One of those early services is <tt>s6-svscan-log</tt>, which is +the catch-all logger. When this service is up, <tt>s6-linux-init<tt>'s +child unblocks. </li> + <li> The child execs into <tt><em>basedir</em>/scripts/rc.init</tt>. +The first argument to <em>rc.init</em> is the chosen runlevel. The kernel +command line, as given by the kernel to <tt>s6-linux-init</tt> (i.e. without +the <tt>key=value</tt> arguments, which were passed into <tt>s6-linux-init</tt>'s +environment and were stored into <em>env_store</em>), makes for the rest of +the arguments given to <em>rc.init</em>. </li> + </ul> </li> +</ul> + +<p> + By the time <em>rc.init</em> runs, +<a href="//skarnet.org/software/s6/s6-svscan.html">s6-svscan</a> is running +as pid 1 and has spawned its early services - at least the catch-all logger, +and the other services, including the early getty if it has been defined, are +started in parallel and will be ready instantly. <em>rc.init</em> can then +perform <em>stage 2</em> of the initialization process, i.e. the initialization +sequence per se. +</p> + +<h2> Notes </h2> + +<ul> + <li> The <tt>s6-linux-init</tt> +binary is not meant to be called directly, or be linked to <tt>/sbin/init</tt> +directly, because it takes command-line options. + Instead, after a +<a href="s6-linux-init-maker.html">s6-linux-init-maker</a> invocation, +the <tt>bin/</tt> subdirectory of the target will contain a script called +<tt>init</tt>, which execs into <tt>s6-linux-init</tt> with the appropriate +command-line options, and <em>is</em> suitable as a <tt>/sbin/init</tt> program. +The <tt>bin/</tt> subdirectory +should be copied by the administrator into <tt>/sbin</tt> for full +interface compatibility with sysvinit. </li> +</ul> + +</body> +</html> |