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<div class="refentry" lang="en">
<a name="man.nsupdate"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p><span class="application">nsupdate</span> — Dynamic DNS update utility</p>
</div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="cmdsynopsis"><p><code class="command">nsupdate</code> [<code class="option">-d</code>] [<code class="option">-D</code>] [[<code class="option">-g</code>] | [<code class="option">-o</code>] | [<code class="option">-l</code>] | [<code class="option">-y <em class="replaceable"><code>[<span class="optional">hmac:</span>]keyname:secret</code></em></code>] | [<code class="option">-k <em class="replaceable"><code>keyfile</code></em></code>]] [<code class="option">-t <em class="replaceable"><code>timeout</code></em></code>] [<code class="option">-u <em class="replaceable"><code>udptimeout</code></em></code>] [<code class="option">-r <em class="replaceable"><code>udpretries</code></em></code>] [<code class="option">-R <em class="replaceable"><code>randomdev</code></em></code>] [<code class="option">-v</code>] [filename]</p></div>
</div>
<div class="refsect1" lang="en">
<a name="id2616486"></a><h2>DESCRIPTION</h2>
<p><span><strong class="command">nsupdate</strong></span>
is used to submit Dynamic DNS Update requests as defined in RFC 2136
to a name server.
This allows resource records to be added or removed from a zone
without manually editing the zone file.
A single update request can contain requests to add or remove more than
one
resource record.
</p>
<p>
Zones that are under dynamic control via
<span><strong class="command">nsupdate</strong></span>
or a DHCP server should not be edited by hand.
Manual edits could
conflict with dynamic updates and cause data to be lost.
</p>
<p>
The resource records that are dynamically added or removed with
<span><strong class="command">nsupdate</strong></span>
have to be in the same zone.
Requests are sent to the zone's master server.
This is identified by the MNAME field of the zone's SOA record.
</p>
<p>
The
<code class="option">-d</code>
option makes
<span><strong class="command">nsupdate</strong></span>
operate in debug mode.
This provides tracing information about the update requests that are
made and the replies received from the name server.
</p>
<p>
The <code class="option">-D</code> option makes <span><strong class="command">nsupdate</strong></span>
report additional debugging information to <code class="option">-d</code>.
</p>
<p>
The <code class="option">-L</code> option with an integer argument of zero or
higher sets the logging debug level. If zero, logging is disabled.
</p>
<p>
Transaction signatures can be used to authenticate the Dynamic
DNS updates. These use the TSIG resource record type described
in RFC 2845 or the SIG(0) record described in RFC 2535 and
RFC 2931 or GSS-TSIG as described in RFC 3645. TSIG relies on
a shared secret that should only be known to
<span><strong class="command">nsupdate</strong></span> and the name server. Currently,
the only supported encryption algorithm for TSIG is HMAC-MD5,
which is defined in RFC 2104. Once other algorithms are
defined for TSIG, applications will need to ensure they select
the appropriate algorithm as well as the key when authenticating
each other. For instance, suitable <span class="type">key</span> and
<span class="type">server</span> statements would be added to
<code class="filename">/etc/named.conf</code> so that the name server
can associate the appropriate secret key and algorithm with
the IP address of the client application that will be using
TSIG authentication. SIG(0) uses public key cryptography.
To use a SIG(0) key, the public key must be stored in a KEY
record in a zone served by the name server.
<span><strong class="command">nsupdate</strong></span> does not read
<code class="filename">/etc/named.conf</code>.
</p>
<p>
GSS-TSIG uses Kerberos credentials. Standard GSS-TSIG mode
is switched on with the <code class="option">-g</code> flag. A
non-standards-compliant variant of GSS-TSIG used by Windows
2000 can be switched on with the <code class="option">-o</code> flag.
</p>
<p><span><strong class="command">nsupdate</strong></span>
uses the <code class="option">-y</code> or <code class="option">-k</code> option
to provide the shared secret needed to generate a TSIG record
for authenticating Dynamic DNS update requests, default type
HMAC-MD5. These options are mutually exclusive.
</p>
<p>
When the <code class="option">-y</code> option is used, a signature is
generated from
[<span class="optional"><em class="parameter"><code>hmac:</code></em></span>]<em class="parameter"><code>keyname:secret.</code></em>
<em class="parameter"><code>keyname</code></em> is the name of the key, and
<em class="parameter"><code>secret</code></em> is the base64 encoded shared secret.
Use of the <code class="option">-y</code> option is discouraged because the
shared secret is supplied as a command line argument in clear text.
This may be visible in the output from
<span class="citerefentry"><span class="refentrytitle">ps</span>(1)</span>
or in a history file maintained by the user's shell.
</p>
<p>
With the
<code class="option">-k</code> option, <span><strong class="command">nsupdate</strong></span> reads
the shared secret from the file <em class="parameter"><code>keyfile</code></em>.
Keyfiles may be in two formats: a single file containing
a <code class="filename">named.conf</code>-format <span><strong class="command">key</strong></span>
statement, which may be generated automatically by
<span><strong class="command">ddns-confgen</strong></span>, or a pair of files whose names are
of the format <code class="filename">K{name}.+157.+{random}.key</code> and
<code class="filename">K{name}.+157.+{random}.private</code>, which can be
generated by <span><strong class="command">dnssec-keygen</strong></span>.
The <code class="option">-k</code> may also be used to specify a SIG(0) key used
to authenticate Dynamic DNS update requests. In this case, the key
specified is not an HMAC-MD5 key.
</p>
<p>
<span><strong class="command">nsupdate</strong></span> can be run in a local-host only mode
using the <code class="option">-l</code> flag. This sets the server address to
localhost (disabling the <span><strong class="command">server</strong></span> so that the server
address cannot be overridden). Connections to the local server will
use a TSIG key found in <code class="filename">/var/run/named/ddns.key</code>,
which is automatically generated by <span><strong class="command">named</strong></span> if any
local master zone has set <span><strong class="command">update-policy</strong></span> to
<span><strong class="command">local</strong></span>. The location of this key file can be
overridden with the <code class="option">-k</code> option.
</p>
<p>
By default, <span><strong class="command">nsupdate</strong></span>
uses UDP to send update requests to the name server unless they are too
large to fit in a UDP request in which case TCP will be used.
The
<code class="option">-v</code>
option makes
<span><strong class="command">nsupdate</strong></span>
use a TCP connection.
This may be preferable when a batch of update requests is made.
</p>
<p>
The <code class="option">-p</code> sets the default port number to use for
connections to a name server. The default is 53.
</p>
<p>
The <code class="option">-t</code> option sets the maximum time an update request
can
take before it is aborted. The default is 300 seconds. Zero can be
used
to disable the timeout.
</p>
<p>
The <code class="option">-u</code> option sets the UDP retry interval. The default
is
3 seconds. If zero, the interval will be computed from the timeout
interval
and number of UDP retries.
</p>
<p>
The <code class="option">-r</code> option sets the number of UDP retries. The
default is
3. If zero, only one update request will be made.
</p>
<p>
The <code class="option">-R <em class="replaceable"><code>randomdev</code></em></code> option
specifies a source of randomness. If the operating system
does not provide a <code class="filename">/dev/random</code> or
equivalent device, the default source of randomness is keyboard
input. <code class="filename">randomdev</code> specifies the name of
a character device or file containing random data to be used
instead of the default. The special value
<code class="filename">keyboard</code> indicates that keyboard input
should be used. This option may be specified multiple times.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2629654"></a><h2>INPUT FORMAT</h2>
<p><span><strong class="command">nsupdate</strong></span>
reads input from
<em class="parameter"><code>filename</code></em>
or standard input.
Each command is supplied on exactly one line of input.
Some commands are for administrative purposes.
The others are either update instructions or prerequisite checks on the
contents of the zone.
These checks set conditions that some name or set of
resource records (RRset) either exists or is absent from the zone.
These conditions must be met if the entire update request is to succeed.
Updates will be rejected if the tests for the prerequisite conditions
fail.
</p>
<p>
Every update request consists of zero or more prerequisites
and zero or more updates.
This allows a suitably authenticated update request to proceed if some
specified resource records are present or missing from the zone.
A blank input line (or the <span><strong class="command">send</strong></span> command)
causes the
accumulated commands to be sent as one Dynamic DNS update request to the
name server.
</p>
<p>
The command formats and their meaning are as follows:
</p>
<div class="variablelist"><dl>
<dt><span class="term">
<span><strong class="command">server</strong></span>
{servername}
[port]
</span></dt>
<dd><p>
Sends all dynamic update requests to the name server
<em class="parameter"><code>servername</code></em>.
When no server statement is provided,
<span><strong class="command">nsupdate</strong></span>
will send updates to the master server of the correct zone.
The MNAME field of that zone's SOA record will identify the
master
server for that zone.
<em class="parameter"><code>port</code></em>
is the port number on
<em class="parameter"><code>servername</code></em>
where the dynamic update requests get sent.
If no port number is specified, the default DNS port number of
53 is
used.
</p></dd>
<dt><span class="term">
<span><strong class="command">local</strong></span>
{address}
[port]
</span></dt>
<dd><p>
Sends all dynamic update requests using the local
<em class="parameter"><code>address</code></em>.
When no local statement is provided,
<span><strong class="command">nsupdate</strong></span>
will send updates using an address and port chosen by the
system.
<em class="parameter"><code>port</code></em>
can additionally be used to make requests come from a specific
port.
If no port number is specified, the system will assign one.
</p></dd>
<dt><span class="term">
<span><strong class="command">zone</strong></span>
{zonename}
</span></dt>
<dd><p>
Specifies that all updates are to be made to the zone
<em class="parameter"><code>zonename</code></em>.
If no
<em class="parameter"><code>zone</code></em>
statement is provided,
<span><strong class="command">nsupdate</strong></span>
will attempt determine the correct zone to update based on the
rest of the input.
</p></dd>
<dt><span class="term">
<span><strong class="command">class</strong></span>
{classname}
</span></dt>
<dd><p>
Specify the default class.
If no <em class="parameter"><code>class</code></em> is specified, the
default class is
<em class="parameter"><code>IN</code></em>.
</p></dd>
<dt><span class="term">
<span><strong class="command">ttl</strong></span>
{seconds}
</span></dt>
<dd><p>
Specify the default time to live for records to be added.
The value <em class="parameter"><code>none</code></em> will clear the default
ttl.
</p></dd>
<dt><span class="term">
<span><strong class="command">key</strong></span>
{name}
{secret}
</span></dt>
<dd><p>
Specifies that all updates are to be TSIG-signed using the
<em class="parameter"><code>keyname</code></em> <em class="parameter"><code>keysecret</code></em> pair.
The <span><strong class="command">key</strong></span> command
overrides any key specified on the command line via
<code class="option">-y</code> or <code class="option">-k</code>.
</p></dd>
<dt><span class="term">
<span><strong class="command">prereq nxdomain</strong></span>
{domain-name}
</span></dt>
<dd><p>
Requires that no resource record of any type exists with name
<em class="parameter"><code>domain-name</code></em>.
</p></dd>
<dt><span class="term">
<span><strong class="command">prereq yxdomain</strong></span>
{domain-name}
</span></dt>
<dd><p>
Requires that
<em class="parameter"><code>domain-name</code></em>
exists (has as at least one resource record, of any type).
</p></dd>
<dt><span class="term">
<span><strong class="command">prereq nxrrset</strong></span>
{domain-name}
[class]
{type}
</span></dt>
<dd><p>
Requires that no resource record exists of the specified
<em class="parameter"><code>type</code></em>,
<em class="parameter"><code>class</code></em>
and
<em class="parameter"><code>domain-name</code></em>.
If
<em class="parameter"><code>class</code></em>
is omitted, IN (internet) is assumed.
</p></dd>
<dt><span class="term">
<span><strong class="command">prereq yxrrset</strong></span>
{domain-name}
[class]
{type}
</span></dt>
<dd><p>
This requires that a resource record of the specified
<em class="parameter"><code>type</code></em>,
<em class="parameter"><code>class</code></em>
and
<em class="parameter"><code>domain-name</code></em>
must exist.
If
<em class="parameter"><code>class</code></em>
is omitted, IN (internet) is assumed.
</p></dd>
<dt><span class="term">
<span><strong class="command">prereq yxrrset</strong></span>
{domain-name}
[class]
{type}
{data...}
</span></dt>
<dd><p>
The
<em class="parameter"><code>data</code></em>
from each set of prerequisites of this form
sharing a common
<em class="parameter"><code>type</code></em>,
<em class="parameter"><code>class</code></em>,
and
<em class="parameter"><code>domain-name</code></em>
are combined to form a set of RRs. This set of RRs must
exactly match the set of RRs existing in the zone at the
given
<em class="parameter"><code>type</code></em>,
<em class="parameter"><code>class</code></em>,
and
<em class="parameter"><code>domain-name</code></em>.
The
<em class="parameter"><code>data</code></em>
are written in the standard text representation of the resource
record's
RDATA.
</p></dd>
<dt><span class="term">
<span><strong class="command">update delete</strong></span>
{domain-name}
[ttl]
[class]
[type [data...]]
</span></dt>
<dd><p>
Deletes any resource records named
<em class="parameter"><code>domain-name</code></em>.
If
<em class="parameter"><code>type</code></em>
and
<em class="parameter"><code>data</code></em>
is provided, only matching resource records will be removed.
The internet class is assumed if
<em class="parameter"><code>class</code></em>
is not supplied. The
<em class="parameter"><code>ttl</code></em>
is ignored, and is only allowed for compatibility.
</p></dd>
<dt><span class="term">
<span><strong class="command">update add</strong></span>
{domain-name}
{ttl}
[class]
{type}
{data...}
</span></dt>
<dd><p>
Adds a new resource record with the specified
<em class="parameter"><code>ttl</code></em>,
<em class="parameter"><code>class</code></em>
and
<em class="parameter"><code>data</code></em>.
</p></dd>
<dt><span class="term">
<span><strong class="command">show</strong></span>
</span></dt>
<dd><p>
Displays the current message, containing all of the
prerequisites and
updates specified since the last send.
</p></dd>
<dt><span class="term">
<span><strong class="command">send</strong></span>
</span></dt>
<dd><p>
Sends the current message. This is equivalent to entering a
blank line.
</p></dd>
<dt><span class="term">
<span><strong class="command">answer</strong></span>
</span></dt>
<dd><p>
Displays the answer.
</p></dd>
<dt><span class="term">
<span><strong class="command">debug</strong></span>
</span></dt>
<dd><p>
Turn on debugging.
</p></dd>
</dl></div>
<p>
</p>
<p>
Lines beginning with a semicolon are comments and are ignored.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2672807"></a><h2>EXAMPLES</h2>
<p>
The examples below show how
<span><strong class="command">nsupdate</strong></span>
could be used to insert and delete resource records from the
<span class="type">example.com</span>
zone.
Notice that the input in each example contains a trailing blank line so
that
a group of commands are sent as one dynamic update request to the
master name server for
<span class="type">example.com</span>.
</p>
<pre class="programlisting">
# nsupdate
> update delete oldhost.example.com A
> update add newhost.example.com 86400 A 172.16.1.1
> send
</pre>
<p>
</p>
<p>
Any A records for
<span class="type">oldhost.example.com</span>
are deleted.
And an A record for
<span class="type">newhost.example.com</span>
with IP address 172.16.1.1 is added.
The newly-added record has a 1 day TTL (86400 seconds).
</p>
<pre class="programlisting">
# nsupdate
> prereq nxdomain nickname.example.com
> update add nickname.example.com 86400 CNAME somehost.example.com
> send
</pre>
<p>
</p>
<p>
The prerequisite condition gets the name server to check that there
are no resource records of any type for
<span class="type">nickname.example.com</span>.
If there are, the update request fails.
If this name does not exist, a CNAME for it is added.
This ensures that when the CNAME is added, it cannot conflict with the
long-standing rule in RFC 1034 that a name must not exist as any other
record type if it exists as a CNAME.
(The rule has been updated for DNSSEC in RFC 2535 to allow CNAMEs to have
RRSIG, DNSKEY and NSEC records.)
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2672857"></a><h2>FILES</h2>
<div class="variablelist"><dl>
<dt><span class="term"><code class="constant">/etc/resolv.conf</code></span></dt>
<dd><p>
used to identify default name server
</p></dd>
<dt><span class="term"><code class="constant">/var/run/named/ddns.key</code></span></dt>
<dd><p>
sets the default TSIG key for use in local-only mode
</p></dd>
<dt><span class="term"><code class="constant">K{name}.+157.+{random}.key</code></span></dt>
<dd><p>
base-64 encoding of HMAC-MD5 key created by
<span class="citerefentry"><span class="refentrytitle">dnssec-keygen</span>(8)</span>.
</p></dd>
<dt><span class="term"><code class="constant">K{name}.+157.+{random}.private</code></span></dt>
<dd><p>
base-64 encoding of HMAC-MD5 key created by
<span class="citerefentry"><span class="refentrytitle">dnssec-keygen</span>(8)</span>.
</p></dd>
</dl></div>
</div>
<div class="refsect1" lang="en">
<a name="id2673009"></a><h2>SEE ALSO</h2>
<p>
<em class="citetitle">RFC 2136</em>,
<em class="citetitle">RFC 3007</em>,
<em class="citetitle">RFC 2104</em>,
<em class="citetitle">RFC 2845</em>,
<em class="citetitle">RFC 1034</em>,
<em class="citetitle">RFC 2535</em>,
<em class="citetitle">RFC 2931</em>,
<span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>,
<span class="citerefentry"><span class="refentrytitle">ddns-confgen</span>(8)</span>,
<span class="citerefentry"><span class="refentrytitle">dnssec-keygen</span>(8)</span>.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2673066"></a><h2>BUGS</h2>
<p>
The TSIG key is redundantly stored in two separate files.
This is a consequence of nsupdate using the DST library
for its cryptographic operations, and may change in future
releases.
</p>
</div>
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