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<title>s6-dns: the s6-dnsname program</title>
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<a href="index.html">s6-dns</a><br />
<a href="//skarnet.org/software/">Software</a><br />
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<h1> The s6-dnsname program </h1>
<p>
s6-dnsname finds the name associated to an IPv4 or IPv6 address.
</p>
<h2> Interface </h2>
<pre>
s6-dnsname [ -4 | -6 ] [ -r ] [ -t <em>timeout</em> ] <em>ip</em>
</pre>
<ul>
<li> s6-dnsname converts the IP address <em>ip</em> to a name
ending in <tt>in-addr.arpa.</tt> or <tt>ip6.arpa.</tt> then makes a
PTR query for this name.
It waits for the result and prints the obtained names, one per line,
then exits 0. </li>
<li> If the domain exists but no relevant field has been found, it exits 1. </li>
<li> If the DNS answered but no answer is available, it prints a relevant
error message and exits 2. </li>
<li> By default, s6-dnsname looks for DNS cache addresses in the
<tt>/etc/resolv.conf</tt> file. If the DNSCACHEIP environment variable is set
and contains a list of IP (v4 or v6) addresses, separated by commas,
semicolons, spaces, tabs, newlines or carriage returns, then this list
is used instead. </li>
</ul>
<h2> Options </h2>
<ul>
<li> <tt>-4</tt> : interpret <em>ip</em> as an IPv4 address. </li>
<li> <tt>-6</tt> : interpret <em>ip</em> as an IPv6 address.
If neither of the <tt>-4</tt> and <tt>-6</tt> is given, or if both are
given, then <em>ip</em> will be interpreted as v4 or v6 depending on
its syntax. </li>
<li> <tt>-r</tt> : random. By default, the program does not sort the
result, but prints them in the order received from the DNS. With this
option, it performs a random permutation on the results before printing
them. </li>
<li> <tt>-t</tt> <em>timeout</em> : if the resolution takes more
than <em>timeout</em> milliseconds, then it exits 99 right away with an error
message. By default, <em>timeout</em> is 0, which means no timeout. </li>
</ul>
<h2> Notes </h2>
<ul>
<li> If the underlying skalibs has been compiled with IPv6 support disabled,
s6-dnsname will not be able to use IPv6 transport for its resolution, but it
will still accept and resolve IPv6 addresses. </li>
</ul>
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