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diff --git a/doc/s6-ipcserver.html b/doc/s6-ipcserver.html new file mode 100644 index 0000000..855fe4b --- /dev/null +++ b/doc/s6-ipcserver.html @@ -0,0 +1,173 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6: the s6-ipcserver program</title> + <meta name="Description" content="s6: the s6-ipcserver program" /> + <meta name="Keywords" content="s6 s6-ipcserver ipcserver ucspi unix server super-server" /> + <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6</a><br /> +<a href="http://skarnet.org/software/">Software</a><br /> +<a href="http://skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>s6-ipcserver</tt> program </h1> + +<p> +<tt>s6-ipcserver</tt> is an +<a href="http://cr.yp.to/proto/ucspi.txt">UCSPI server tool</a> for +Unix domain sockets, i.e. a super-server. +It accepts connections from clients, and forks a +program to handle each connection. +</p> + +<h2> Interface </h2> + +<pre> + s6-ipcserver [ -1 ] [ -q | -Q | -v ] [ -d | -D ] [ -P | -p ] [ -c <em>maxconn</em> ] [ -C <em>localmaxconn</em> ] [ -b <em>backlog</em> ] [ -G <em>gidlist</em> ] [ -g <em>gid</em> ] [ -u <em>uid</em> ] [ -U ] <em>path</em> <em>prog...</em> +</pre> + +<ul> + <li> s6-ipcserver binds a Unix domain socket to <em>path</em>. </li> + <li> It can drop its root privileges. </li> + <li> It closes its stdin and stdout. </li> + <li> For every client connection to this socket, it +forks. The child sets some environment variables, then +executes <em>prog...</em> with stdin reading from the socket and +stdout writing to it. </li> + <li> Depending on the verbosity level, it logs what it does to stderr. </li> + <li> It runs until killed by a signal. Depending on the received +signal, it may kill its children before exiting. </li> + <li> s6-ipcserver actually doesn't do any of this itself. It is +a wrapper, rewriting the command line and executing into a chain +of programs that perform those duties. </li> +</ul> + +<h2> Implementation </h2> + +<ul> + <li> s6-ipcserver parses the options and arguments it is given, and +builds a new command line with them. It then executes into that new +command line. </li> + <li> The first program s6-ipcserver executes into is +<a href="s6-ipcserver-socketbinder.html">s6-ipcserver-socketbinder</a>. +It will create and bind a Unix domain socket to <em>path</em>, then +execute into the rest of the command line. </li> + <li> If a privilege-dropping operation has been requested, the +program that s6-ipcserver-socketbinder executes into is +<a href="s6-applyuidgid.html">s6-applyuidgid</a>. +It will drop the root privileges, then execute into the rest of the +command line. </li> + <li> The next program in the chain is +<a href="s6-ipcserverd.html">s6-ipcserverd</a>. It is executed into +by s6-applyuidgid, or directly by s6-ipcserver-socketbinder if no +privilege-dropping operation has been requested. s6-ipcserverd is +the long-lived process, the "daemon" itself, accepting connections +from clients. </li> + <li> For every client, s6-ipcserverd will spawn an instance of +<em>prog...</em>, the remainder of the command line. </li> +</ul> + + +<h2> Options </h2> + +<ul> + <li> <tt>-1</tt> : write <em>path</em>, followed by a newline, +to stdout, before +closing it, right after binding and listening to the Unix socket. +If stdout is suitably redirected, this can be used by monitoring +programs to check when the server is ready to accept connections. </li> + <li> <tt>-q</tt> : be quiet. </li> + <li> <tt>-Q</tt> : be normally verbose. This is the default. </li> + <li> <tt>-v</tt> : be verbose. </li> + <li> <tt>-d</tt> : allow instant rebinding to the same path +even if it has been used not long ago - this is the SO_REUSEADDR flag to +<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/setsockopt.html">setsockopt()</a> +and is generally used with server programs. This is the default. Note that +<em>path</em> will be deleted if it already exists at program start time. </li> + <li> <tt>-D</tt> : disallow instant rebinding to the same path. </li> + <li> <tt>-P</tt> : disable client credentials lookups. The +IPCREMOTEEUID and IPCREMOTEEGID environment variables will be unset +in every instance of <em>prog...</em>. This is the portable option, +because not every system supports credential lookup across Unix domain +sockets; but it is not as secure. </li> + <li> <tt>-p</tt> : enable client credentials lookups. This +is the default; it works at least on Linux, Solaris, and +*BSD systems. On systems that do not support it, every connection +attempt will fail with a warning message. </li> + <li> <tt>-c <em>maxconn</em></tt> : accept at most +<em>maxconn</em> concurrent connections. Default is 40. It is +impossible to set it higher than 1000. </li> + <li> <tt>-C <em>localmaxconn</em></tt> : accept at most +<em>localmaxconn</em> connections from the same user ID. +Default is 40. It is impossible to set it higher than <em>maxconn</em>. </li> + <li> <tt>-b <em>backlog</em></tt> : set a maximum of +<em>backlog</em> backlog connections on the socket. Extra +connection attempts will rejected by the kernel. </li> + <li> <tt>-G <em>gidlist</em></tt> : change s6-ipcserver's +supplementary group list to <em>gidlist</em> after binding the socket. +This is only valid when run as root. <em>gidlist</em> must be a +comma-separated list of numerical group IDs. </li> + <li> <tt>-g <em>gid</em></tt> : change s6-ipcserver's groupid +to <em>gid</em> after binding the socket. This is only valid when run +as root. </li> + <li> <tt>-u <em>uid</em></tt> : change s6-ipcserver's userid +to <em>uid</em> after binding the socket. This is only valid when run +as root. </li> + <li> <tt>-U</tt> : change s6-ipcserver's user id, group id and +supplementary group list +according to the values of the UID, GID and GIDLIST environment variables +after binding the socket. This is only valid when run as root. +This can be used with the +<a href="s6-envuidgid.html">s6-envuidgid</a> +program to easily script a service that binds to a privileged socket +then drops its privileges to those of a named non-root account. </li> +</ul> + +<h2> Implementation </h2> + +<ul> + <li> s6-ipcserver parses the options and arguments it is given, and +builds a new command line with them. It then executes into that new +command line. </li> + <li> The first program s6-ipcserver executes into is +<a href="s6-ipcserver-socketbinder.html">s6-ipcserver-socketbinder</a>. +It will create and bind a Unix domain socket to <em>path</em>, then +execute into the rest of the command line. </li> + <li> If a privilege-dropping operation has been requested, the +program that s6-ipcserver-socketbinder executes into is +<a href="s6-applyuidgid.html">s6-applyuidgid</a>. +It will drop the root privileges, then execute into the rest of the +command line. </li> + <li> The next program in the chain is +<a href="s6-ipcserverd.html">s6-ipcserverd</a>. It is executed into +by s6-applyuidgid, or directly by s6-ipcserver-socketbinder if no +privilege-dropping operation has been requested. s6-ipcserverd is +the long-lived process, the "daemon" itself, accepting connections +from clients. </li> + <li> For every client, s6-ipcserverd will spawn an instance of +<em>prog...</em>, the remainder of the command line. </li> +</ul> + +<h2> Notes </h2> + +<ul> + <li> s6-ipcserver does not interpret its options itself. It just +dispatches them to the appropriate program on the command line that +it builds. </li> + <li> Previous versions of s6-ipcserver were +monolithic: it did the work of s6-ipcserver-socketbinder, +s6-applyuidgid and s6-ipcserverd itself. The functionality has now +been split into several different programs because some service startup +schemes require the daemon to get its socket from an external +program instead of creating and binding it itself. The most obvious +application of this is upgrading a long-lived process without +losing existing connections. </li> +</ul> + +</body> +</html> |