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<title>s6-dns: the s6-dnsip program</title>
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<p>
<a href="index.html">s6-dns</a><br />
<a href="//skarnet.org/software/">Software</a><br />
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<h1> The s6-dnsip program </h1>
<p>
s6-dnsip finds both the IPv6 and IPv4 addresses associated to a domain name.
</p>
<h2> Interface </h2>
<pre>
s6-dnsip [ -q ] [ -H | -h ] [ -r ] [ -t <em>timeout</em> ] <em>domain</em>
</pre>
<ul>
<li> s6-dnsip makes both an A and an AAAA query for the name <em>domain</em>,
in parallel. It waits for the results and prints the obtained addresses,
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-dnsip 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>-q</tt> : qualify. Qualifies <em>domain</em> before resolution,
according to suffixes found in <tt>/etc/resolv.conf</tt>. If the DNSQUALIFY
environment variable is set and contains a list of suffixes separated by spaces,
tabs, newlines or carriage returns, then this list is used instead. By
default, no qualification is used: if <em>domain</em> is not a FQDN, a dot
is just appended to it. </li>
<li> <tt>-H</tt> : do not use data from <tt>/etc/hosts</tt>. This is
the default. </li>
<li> <tt>-h</tt> : use data from <tt>/etc/hosts</tt>, if available.
If there's a compiled <tt>/etc/hosts.cdb</tt> file that is newer than <tt>/etc/hosts</tt>,
it will be used instead. (See
<a href="s6-dns-hosts-compile.html">s6-dns-hosts-compile</a> for details.)
If the lookup in the hosts database returns at least one result, then
no DNS lookup is performed. </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>
<p>
Even if the underlying skalibs has been compiled without IPv6 support,
or IPv6 DNS transport is unavailable for any reason, s6-dnsip will still
return IPv6 addresses if the AAAA query has a positive result.
</p>
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