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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2015-06-17 10:06:12 +0000 |
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| committer | Laurent Bercot <ska-skaware@skarnet.org> | 2015-06-17 10:06:12 +0000 |
| commit | f588272b8055c615df73094d77ceb179a1182219 (patch) | |
| tree | 4c66df45d3621c0f741e500a8cc98de551f8b2f0 /doc/s6-linux-init-maker.html | |
| download | s6-linux-init-f588272b8055c615df73094d77ceb179a1182219.tar.xz | |
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diff --git a/doc/s6-linux-init-maker.html b/doc/s6-linux-init-maker.html new file mode 100644 index 0000000..3c27a2f --- /dev/null +++ b/doc/s6-linux-init-maker.html @@ -0,0 +1,276 @@ +<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-maker program</title> + <meta name="Description" content="s6-linux-init: the s6-linux-init-maker program" /> + <meta name="Keywords" content="s6 linux administration root init maker" /> + <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6-linux-init</a><br /> +<a href="http://skarnet.org/software/">Software</a><br /> +<a href="http://skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>s6-linux-init-maker</tt> program </h1> + +<p> +<tt>s6-linux-init-maker</tt> reads configuration options on +the command line, and outputs a directory to place in the +root filesystem as well as a script suitable as an init program. +</p> + +<p> + s6-linux-init-maker only writes scripts. At boot time, these +scripts will call commands provided by other skarnet.org packages +such as +<a href="http://skarnet.org/software/execline/">execline</a> or +<a href="http://skarnet.org/software/s6/">s6</a>. It is the +responsibility of the administrator to make sure that all the +dependencies are properly installed at boot time, and that the +correct options have been given to s6-linux-init-maker so that +the programs are found <em>on the root filesystem of the +machine</em> - else the scripts will crash. +</p> + +</p> + +<h2> Interface and usage </h2> + +<pre> + s6-linux-init-maker \ + [ -c <em>basedir</em> ] \ + [ -l <em>tmpfsdir</em> ] \ + [ -b <em>execline_bindir</em> ] \ + [ -u <em>log_user</em> ] \ + [ -g <em>early_getty</em> ] \ + [ -2 <em>stage2</em> ] \ + [ -3 <em>stage3</em> ] \ + [ -p <em>initial_path</em> ] \ + [ -m <em>initial_umask</em> ] \ + [ -t <em>timestamp_style</em> ] \ + [ -d <em>dev_style</em> ] \ + [ -e <em>initial_envvar</em> ] ... \ + <em>dir</em> > <em>stage1</em> +</pre> + +<ul> + <li> s6-linux-init-maker should be run as root. </li> + <li> s6-linux-init-maker parses options on its command line. </li> + <li> It writes data into a directory <em>dir</em>, which must not +exist beforehand. </li> + <li> It then prints a script to its standard output. </li> + <li> It exits 0 if everything went well, 100 if a user error occurred, +and 111 if a problem occurred during the directory or script creation. </li> +</ul> + +<p> + <em>dir</em> should then be copied by the administrator to the place +declared as <em>basedir</em>. Be careful: it contains fifos, files with +precise uid/gid permissions, and files with non-standard access rights, +so be sure to copy it verbatim. The +<a href="http://skarnet.org/software/s6-portable-utils/s6-hiercopy.html">s6-hiercopy</a> +tool can do it, as well as the GNU or busybox <tt>cp -a</tt> command. +</p> + +<p> + The <em>stage1</em> script printed by s6-linux-init-maker on its +stdout is then suitable as an init program. The administrator should +copy it to <tt>/sbin/init</tt> and make it executable. +</p> + +<h2> Boot sequence </h2> + +<p> + When the kernel boots, it runs the <em>stage1</em> script, and this is +what happens: +</p> + +<ul> + <li> <em>stage1</em> is an +<a href="http://skarnet.org/software/execline/">execline</a> script, so +the first process run by the kernel is the +<a href="http://skarnet.org/software/execline/execlineb.html">execlineb</a> +program launcher. </li> + <li> <em>stage1</em> mounts a +<a href="https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt">tmpfs</a> +filesystem on <em>tmpfsdir</em>. </li> + <li> <em>stage1</em> copies <tt><em>basedir</em>/run-image</tt> verbatim to +<em>tmpfsdir</em>. </li> + <li> <em>stage1</em> reads a global set of environment variables from the +<tt><em>basedir</em>/env</tt> +<a href="http://skarnet.org/software/s6/s6-envdir.html">environment directory</a>. </li> + <li> <em>stage1</em> forks a child that will block until +<a href="http://skarnet.org/software/s6/s6-svscan.html">s6-svscan</a> is running. </li> + <li> <em>stage1</em> executes, as process 1, into +<a href="http://skarnet.org/software/s6/s6-svscan.html">s6-svscan</a>, +with <tt><em>tmpfsdir</em>/service</tt> as a +<a href="http://skarnet.org/software/s6/scandir.html">scan directory</a>. </li> + <li> This scan directory already contains at least one service, which is the +<em>catch-all logger</em>: error messages from the supervision tree, and +from services that do not have a dedicated logger, are handled by a +special <a href="http://skarnet.org/software/s6/s6-log.html">s6-log</a> +instance and made available in <tt><em>tmpfsdir</em>/uncaught-logs</tt> +instead of clogging the system console. </li> + <li> If the <tt>-g</tt> option has been given to s6-linux-init-maker, the +scan directory will also contain a service for an early getty. </li> + <li> s6-svscan starts all the services defined in the scan directory, +and unblocks the child forked by <em>stage1</em>. </li> + <li> This child executes into <em>stage2</em>. </li> +</ul> + +<p> + <em>stage2</em> is the responsibility of the administrator - it will +not be written automatically! +It should +contain all the necessary initialization sequence to bring up a proper +system. When <em>stage2</em> is executed, the machine state is as follows: +</p> + +<ul> + <li> <em>stage2</em>'s working directory is <tt>/</tt> and its stdin +is <tt>/dev/null</tt>. <em>stage2</em>'s +stdout and stderr both point to the pipe to the catch-all logger, so +unless redirected, <em>stage2</em>'s output will be logged into the +<tt><em>tmpfsdir/uncaught-logs</em></tt> directory. </li> + <li> The system has a valid device directory mounted on <tt>/dev</tt>. + <li> Depending on the kernel boot command line, the root filesystem +may be in read-only mode. </li> + <li> There is a tmpfs available for root only in <em>tmpfsdir</em>. </li> + <li> <a href="http://skarnet.org/software/s6/s6-svscan.html">s6-svscan</a> +is running as process 1. At any time, it is possible to make it supervise a long-lived +process by linking the appropriate +<a href="http://skarnet.org/software/s6/servicedir.html">service directory</a> +into <tt><em>tmpfsdir</em>/service</tt>, then running the command +<tt>s6-svscanctl -a <em>tmpfsdir</em>/service</tt>. Services without a +dedicated logger will send their output to the catch-all logger. </li> + <li> A getty service may already be available. The point of this early +getty is essentially to make it easier to debug if <em>stage2</em> fails. </li> +</ul> + +<p> + There is <em>nothing else</em>. In particular, no filesystem has been +mounted yet, including <tt>/proc</tt> and <tt>/sys</tt>; and no one-time +initialization +has been performed. The point of <em>stage1</em> is only to make it +possible to run <em>stage2</em> with a logging infrastructure and a +supervision infrastructure already available, and all the +real machine and service initialization should happen in <em>stage2</em>. +</p> + +<h2> Shutdown sequence </h2> + +<p> + When s6-svscan is told to exit via an appropriate +<a href="http://skarnet.org/software/s6/s6-svscanctl.html">s6-svscanctl</a> +command, it executes into the <em>stage3</em> script, which, like +<em>stage2</em>, is the responsibility of the administrator. <em>stage3</em> +is run in the following state: +</p> + +<ul> + <li> It runs as process 1. (Doing so makes it easier to recover after +killing all processes by <tt>kill -9 -1</tt> or +<a href="http://skarnet.org/software/s6-portable-utils/s6-nuke.html">s6-nuke</a>). </li> + <li> Its working directory is <tt>/</tt> and its stdin is <tt>/dev/null</tt> </li> + <li> Its stdout and stderr are both <tt>/dev/console</tt> </li> + <li> Depending on the exact s6-svscanctl command that terminated s6-svscan, +and what has happened before that command was sent, there may or may not be +long-running services that remain alive. The catch-all logger and its +supervisor will <em>always</em> be alive, which is not a problem because they +do not hold any file descriptor to a filesystem that would need to be +unmounted. </li> +</ul> + +<h2> s6-linux-init-maker options </h2> + +<ul> + <li> <tt>-c</tt> <em>basedir</em> : at boot time, <em>stage1</em> +will read its read-only data from <em>basedir</em>. After running +s6-linux-init-maker, the administrator should make sure to copy the +created directory <em>dir</em> to <em>basedir</em>. <em>basedir</em> +must be absolute. Default is +<strong><tt>/etc/s6</tt></strong>. </li> <p /> + + <li> <tt>-l</tt> <em>tmpfsdir</em> : at boot time, a tmpfs will +be mounted on <em>tmpfsdir</em>. The directory should already exist in +the root filesystem, and be empty. <em>tmpfsdir</em> must be absolute. Default is +<strong><tt>/run</tt></strong>. </li> <p /> + + <li> <tt>-b</tt> <em>execline_bindir</em> : init is run by the kernel +without a PATH, and since it is a script, it is necessary to tell it where +to find the +<a href="http://skarnet.org/software/execline/execlineb.html">execlineb</a> +launcher and the first few early commands before PATH can be set. +<em>execline_bindir</em> is the location where the execline binaries can be +found. It must be absolute. Default is +<strong><tt>/bin</tt></strong>. </li> <p /> + + <li> <tt>-u</tt> <em>log_user</em> : the catch-all +logger will not run as root, but as <em>log_user</em>. Default is +<strong><tt>nobody</tt></strong>. </li> <p /> + + <li> <tt>-g</tt> <em>early_getty</em> : if this option +is set, s6-linux-init-maker will define a service that will run +very early, before <em>stage2</em> is executed. This early service +should be a getty, to allow logins even if <em>stage2</em> fails. +<em>early_getty</em> should be a simple command line: for instance, +<tt>"/sbin/getty 38400 tty1"</tt>. By default, no early service +is defined. </li> <p /> + + <li> <tt>-2</tt> <em>stage2</em> : <em>stage2</em> is +the location of the stage 2 script that will be run when the +system has an operational supervision tree. It must be absolute. Default is +<strong><tt>/etc/rc.init</tt></strong>. </li> <p /> + + <li> <tt>-3</tt> <em>stage3</em> : <em>stage3</em> is +the location of the stage 3 script that will be run at the end of +the machine lifetime, when s6-svscan is told to terminate. +It must be absolute. Default is +<strong><tt>/etc/rc.shutdown</tt></strong>. </li> <p /> + + <li> <tt>-p</tt> <em>initial_path</em> : the value to +set the PATH environment variable to, for all the starting processes. +This will be done as early as possible in <em>stage1</em>. Default is +the value that has been compiled in +<a href="http://skarnet.org/software/skalibs/">skalibs</a> via the +<tt>--with-default-path</tt> configure option, i.e. by default +<strong><tt>/usr/bin:/bin</tt></strong>. </li> <p /> + + <li> <tt>-m</tt> <em>initial_umask</em> : the value of +the initial file umask for all the starting processes, in octal. +Default is +<strong><tt>022</tt></strong>. </li> <p /> + + <li> <tt>-t</tt> <em>timestamp_style</em> : how +logs are timestamped by the catch-all logger. 0 means no +timestamp, 1 means +<a href="http://cr.yp.to/libtai/tai64.html">external TAI64N format</a>, +2 means +<a href="http://www.iso.org/iso/home/standards/iso8601.htm">ISO 8601 format</a>, +and 3 means both. Default is +<strong><tt>1</tt></strong>. </li> <p /> + + <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. Default is +<strong><tt>2</tt></strong>. </li> <p /> + + <li> <tt>-e</tt> <em>initial_envvar</em> : this option +can be repeated. For every <em>initial_envvar</em>, s6-linux-init-maker +will adjust the global environment directory in <em>dir</em>/env. +<em>initial_envvar</em> must either be of the form <em>VAR</em>, +to make sure that <em>VAR</em> does not appear in the global +environment, or of the form <em>VAR=VALUE</em>, to add an +environment variable <em>VAR</em> with the value <em>VALUE</em>. +The TZ variable, for instance, is a good candidate to be set in +the global environment. </li> <p /> +</ul> + +</body> +</html> |