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diff --git a/doc/s6-dns-hosts-compile.html b/doc/s6-dns-hosts-compile.html new file mode 100644 index 0000000..c499ded --- /dev/null +++ b/doc/s6-dns-hosts-compile.html @@ -0,0 +1,75 @@ +<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-dns: the s6-dns-hosts-compile program</title> + <meta name="Description" content="s6-dns: the s6-dns-hosts-compile program" /> + <meta name="Keywords" content="s6-dns s6-dns-hosts-compile /etc/hosts /etc/hosts.cdb hosts file cdb" /> + <!-- <link rel="stylesheet" type="text/css" href="//skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6-dns</a><br /> +<a href="//skarnet.org/software/">Software</a><br /> +<a href="//skarnet.org/">skarnet.org</a> +</p> + +<h1> The s6-dns-hosts-compile program </h1> + +<p> + s6-dns-hosts-compile compiles the system's <tt>/etc/hosts</tt> file into a +CDB file for more efficient later use by s6-dns programs that may use the +data contained in the hosts file. +</p> + +<h2> Interface </h2> + +<pre> + s6-dns-hosts-compile [ -i <em>ifile</em> ] [ -o <em>ofile</em> ] +</pre> + +<ul> + <li> s6-randomip reads the <tt>/etc/hosts</tt> file, which must follow the +<a href="https://man7.org/linux/man-pages/man5/hosts.5.html">traditional hosts format</a>. </li> + <li> It outputs a CDB database in the <tt>/etc/hosts.cdb</tt> file. </li> + <li> It exits 0. </li> +</ul> + +<h2> Options </h2> + +<ul> + <li> <tt>-i</tt> <em>ifile</em> : read from <em>ifile</em> instead of <tt>/etc/hosts</tt>. </li> + <li> <tt>-o</tt> <em>ofile</em> : write to <em>ofile</em> instead of <tt>/etc/hosts.cdb</tt>. </li> +</ul> + +<h2> Notes </h2> + +<ul> + <li> The <tt>/etc/hosts</tt> file is an old way of specifying IP from/to domain +name correspondences. It's convenient in a pinch when a user needs to locally +override DNS data - for instance, to redirect common advertising sites to 127.0.0.1 - +but it does not map exactly to the DNS view of domain names. </li> + <li> Due to this, and to its line-by-line text syntax, lookups using this file +are terribly inefficient and rely on approximate qualification heuristics. </li> + <li> To avoid that, s6-dns tools prefer having the <tt>/etc/hosts</tt> data in +a format that's both more DNS-like and more efficient; the file output by +s6-dns-hosts-compile is the result. </li> + <li> When asked to take <tt>/etc/hosts</tt> data into account, s6-dns tools will +first look for a <tt>/etc/hosts.cdb</tt> file and use the data from it. If +absent, they will read the <tt>/etc/hosts</tt> file and compile its contents +into a temporary cdb file under <tt>/tmp</tt> (which they immediately unlink), +and use that cdb to query hosts data. </li> + <li> As a consequence, lookups are always efficient, but there's an initial +compilation step. Using s6-dns-hosts-compile to produce a <tt>/etc/hosts.cdb</tt> +file in advance saves the cost of that compilation step in subsequent +invocations of s6-dns tools. </li> + <li> If s6-dns tools detect that <tt>/etc/hosts</tt> has been modified more recently +than <tt>/etc/hosts.cdb</tt>, they will not use <tt>/etc/hosts.cdb</tt> and will +perform the compilation step into a temporary file. So, remember to run +s6-dns-hosts-compile after modifying your <tt>/etc/hosts</tt>. </li> +</ul> + +</body> +</html> |