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diff --git a/doc/s6-fdholder-daemon.html b/doc/s6-fdholder-daemon.html new file mode 100644 index 0000000..90adea0 --- /dev/null +++ b/doc/s6-fdholder-daemon.html @@ -0,0 +1,147 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6: the s6-fdholder-daemon program</title> + <meta name="Description" content="s6: the s6-fdholder-daemon program" /> + <meta name="Keywords" content="s6 s6-fdholder fd-holding fd-holder fd unix socket activation server daemon" /> + <!-- <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-fdholder-daemon</tt> program </h1> + +<p> +<tt>s6-fdholder-daemon</tt> is a fd-holding <em>daemon</em>, i.e. a +long-lived program. +It listens on a Unix domain socket, then +accepts client connections; +it stores file descriptors on behalf of clients, along with an identifier +for every file descriptor stored, and possibly an expiration date (after +which the file descriptor will be forgotten). It also allows clients to +retrieve a file descriptor by its identifier. +</p> + +<h2> Interface </h2> + +<pre> + s6-fdholder-daemon [ -1 ] [ -v <em>verbosity</em> ] [ -d | -D ] [ -c <em>maxconn</em> ] [ -n <em>maxfds</em> ] [ -b <em>backlog</em> ] [ -G <em>gidlist</em> ] [ -g <em>gid</em> ] [ -u <em>uid</em> ] [ -U ] [ -t <em>clienttimeout</em> ] [ -T <em>lameducktimeout</em> ] [ -i <em>rulesdir</em> | -x <em>rulesfile</em> ] <em>path</em> +</pre> + +<ul> + <li> s6-fdholder-daemon 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-fdholder-daemon 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 last program in the chain is +<a href="s6-fdholderd.html">s6-fdholderd</a>. It is executed into +by s6-applyuidgid, or directly by s6-ipcserver-socketbinder if no +privilege-dropping operation has been requested. s6-fdholderd is +the long-lived process, the daemon itself, performing fd holding and +accepting connections from clients. </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>-v <em>verbosity</em></tt> : be quiet, normally +verbose, or more verbose, depending on if <em>verbosity</em> is 0, +1, or more. The default is 1. </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>-c <em>maxconn</em></tt> : accept at most +<em>maxconn</em> concurrent client connections. Default is 16. It is +impossible to set it higher than the value of the S6_FDHOLDER_MAX macro, +which is 256. Client connections to this server are short-lived, so this +number needs not be too high. Every client connection eats up +one available file descriptor, so it is best for <em>maxconn</em> to be +as small as possible. </li> + <li> <tt>-n <em>maxfds</em></tt> : store at most +<em>maxfds</em> file descriptors. Default is 1000. +It is impossible to set it higher than the number of files that can +be opened by the s6-fdholder-daemon process minus a few descriptors +needed for correct <a href="s6-fdholderd.html">s6-fdholderd</a> +operation. Before running s6-fdholder-daemon, make sure to +<a href="s6-softlimit.html">properly adjust</a> the +<a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_resource.h.html">number +of openable files</a> of the current process. </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-fdholder-daemon'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-fdholder-daemon'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-fdholder-daemon'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-fdholder-daemon'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> + <li> <tt>-t <em>clienttimeout</em></tt> : disconnect a client +if it's in the middle of an operation and it has not written or read any +data in <em>clienttimeout</em> milliseconds. By default, <em>clienttimeout</em> +is 0, which means infinite. </li> + <li> <tt>-T <em>lameducktimeout</em></tt> : give clients +<em>lameducktimeout</em> milliseconds to finish their current operation +before exiting after s6-fdholderd has received a SIGTERM. By default, +<em>lameducktimeout</em> is 0, which means infinite. </li> + <li> <tt>-x <em>rulesfile</em></tt> : read access rights +configuration from CDB file <em>rulesfile</em>. </li> + <li> <tt>-i <em>rulesdir</em></tt> : read access rights +configuration from the filesystem in directory <em>rulesdir</em>. </li> +</ul> + +<h2> Notes </h2> + +<ul> + <li> s6-fdholder-daemon does not interpret its options itself. It just +dispatches them to the appropriate program on the command line that +it builds. </li> + <li> From the user's point of view, s6-fdholder-daemon behaves like a +long-lived process, even if the long-lived process itself is called +<a href="s6-fdholderd.html">s6-fdholderd</a>. Every operational detail +of s6-fdholderd applies to s6-fdholder-daemon as well; in particular, +make sure to properly +<a href="s6-fdholderd.html#configuration">configure the clients' +access rights</a>. </li> + <li> s6-fdholder-daemon is meant to be used in a s6 run script, as +a supervised local service. It does not fork itself or write to syslog. +However, it can be run under any infrastructure, including other +supervision infrastructures, OpenRC, systemd, or SysV scripts. </li> +</ul> + +</body> +</html> |