systemd/man/systemd-resolve.xml

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<refentry id="systemd-resolve" conditional='ENABLE_RESOLVE'
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-resolve</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-resolve</refentrytitle>
    <manvolnum>1</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-resolve</refname>
    <refpurpose>Resolve domain names, IPV4 and IPv6 addresses, DNS resource records, and services</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>systemd-resolve</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain" rep="repeat"><replaceable>HOSTNAME</replaceable></arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-resolve</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="plain" rep="repeat"><replaceable>ADDRESS</replaceable></arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-resolve</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <command> --type=<replaceable>TYPE</replaceable></command>
      <arg choice="plain" rep="repeat"><replaceable>DOMAIN</replaceable></arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-resolve</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <command> --service</command>
      <arg choice="plain"><arg choice="opt"><arg choice="opt"><replaceable>NAME</replaceable></arg>
      <replaceable>TYPE</replaceable></arg> <replaceable>DOMAIN</replaceable></arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-resolve</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <command> --openpgp</command>
      <arg choice="plain"><replaceable>USER@DOMAIN</replaceable></arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-resolve</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <command> --tlsa</command>
      <arg choice="plain"><replaceable>DOMAIN<optional>:PORT</optional></replaceable></arg>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-resolve</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <command> --statistics</command>
    </cmdsynopsis>

    <cmdsynopsis>
      <command>systemd-resolve</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <command> --reset-statistics</command>
    </cmdsynopsis>

  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>systemd-resolve</command> may be used to resolve domain names, IPv4 and IPv6 addresses, DNS resource
    records and services with the
    <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    resolver service. By default, the specified list of parameters will be resolved as hostnames, retrieving their IPv4
    and IPv6 addresses. If the parameters specified are formatted as IPv4 or IPv6 operation the reverse operation is
    done, and a hostname is retrieved for the specified addresses.</para>

    <para>The program's output contains information about the protocol used for the look-up and on which network
    interface the data was discovered. It also contains information on whether the information could be
    authenticated. All data for which local DNSSEC validation succeeds is considered authenticated. Moreover all data
    originating from local, trusted sources is also reported authenticated, including resolution of the local host
    name, the <literal>localhost</literal> host name or all data from <filename>/etc/hosts</filename>.</para>

    <para>The <option>--type=</option> switch may be used to specify a DNS resource record type (A, AAAA, SOA, MX, …) in
    order to request a specific DNS resource record, instead of the address or reverse address lookups.
    The special value <literal>help</literal> may be used to list known values.</para>

    <para>The <option>--service</option> switch may be used to resolve <ulink
    url="https://tools.ietf.org/html/rfc2782">SRV</ulink> and <ulink
    url="https://tools.ietf.org/html/rfc6763">DNS-SD</ulink> services (see below). In this mode, between one and three
    arguments are required. If three parameters are passed the first is assumed to be the DNS-SD service name, the
    second the SRV service type, and the third the domain to search in. In this case a full DNS-SD style SRV and TXT
    lookup is executed. If only two parameters are specified, the first is assumed to be the SRV service type, and the
    second the domain to look in. In this case no TXT RR is requested. Finally, if only one parameter is specified, it
    is assumed to be a domain name, that is already prefixed with an SRV type, and an SRV lookup is done (no
    TXT).</para>

    <para>The <option>--openpgp</option> switch may be used to query PGP keys stored as
    <ulink url="https://tools.ietf.org/html/rfc7929">OPENPGPKEY</ulink> resource records.
    When this option is specified one or more e-mail address must be specified.</para>

    <para>The <option>--tlsa</option> switch maybe be used to query TLS public
    keys stored as
    <ulink url="https://tools.ietf.org/html/rfc6698">TLSA</ulink> resource records.
    When this option is specified one or more domain names must be specified.</para>

    <para>The <option>--statistics</option> switch may be used to show resolver statistics, including information about
    the number of successful and failed DNSSEC validations.</para>

    <para>The <option>--reset-statistics</option> may be used to reset various statistics counters maintained the
    resolver, including those shown in the <option>--statistics</option> output. This operation requires root
    privileges.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>
    <variablelist>
      <varlistentry>
        <term><option>-4</option></term>
        <term><option>-6</option></term>

        <listitem><para>By default, when resolving a hostname, both IPv4 and IPv6
        addresses are acquired. By specifying <option>-4</option> only IPv4 addresses are requested, by specifying
        <option>-6</option> only IPv6 addresses are requested.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-i</option> <replaceable>INTERFACE</replaceable></term>
        <term><option>--interface=</option><replaceable>INTERFACE</replaceable></term>

        <listitem><para>Specifies the network interface to execute the query on. This may either be specified as numeric
        interface index or as network interface string (e.g. <literal>en0</literal>). Note that this option has no
        effect if system-wide DNS configuration (as configured in <filename>/etc/resolv.conf</filename> or
        <filename>/etc/systemd/resolve.conf</filename>) in place of per-link configuration is used.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-p</option> <replaceable>PROTOCOL</replaceable></term>
        <term><option>--protocol=</option><replaceable>PROTOCOL</replaceable></term>

        <listitem><para>Specifies the network protocol for the query. May be one of <literal>dns</literal>
        (i.e. classic unicast DNS), <literal>llmnr</literal> (<ulink
        url="https://tools.ietf.org/html/rfc4795">Link-Local Multicast Name Resolution</ulink>),
        <literal>llmnr-ipv4</literal>, <literal>llmnr-ipv6</literal> (LLMNR via the indicated underlying IP
        protocols), <literal>mdns</literal> (<ulink url="https://www.ietf.org/rfc/rfc6762.txt">Multicast DNS</ulink>),
        <literal>mdns-ipv4</literal>, <literal>mdns-ipv6</literal> (MDNS via the indicated underlying IP protocols).
        By default the lookup is done via all protocols suitable for the lookup. If used, limits the set of
        protocols that may be used. Use this option multiple times to enable resolving via multiple protocols at the
        same time. The setting <literal>llmnr</literal> is identical to specifying this switch once with
        <literal>llmnr-ipv4</literal> and once via <literal>llmnr-ipv6</literal>. Note that this option does not force
        the service to resolve the operation with the specified protocol, as that might require a suitable network
        interface and configuration.
        The special value <literal>help</literal> may be used to list known values.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>-t</option> <replaceable>TYPE</replaceable></term>
        <term><option>--type=</option><replaceable>TYPE</replaceable></term>
        <term><option>-c</option> <replaceable>CLASS</replaceable></term>
        <term><option>--class=</option><replaceable>CLASS</replaceable></term>

        <listitem><para>Specifies the DNS resource record type (e.g. A, AAAA, MX, …) and class (e.g. IN, ANY, …) to
        look up. If these options are used a DNS resource record set matching the specified class and type is
        requested. The class defaults to IN if only a type is specified.
        The special value <literal>help</literal> may be used to list known values.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--service</option></term>

        <listitem><para>Enables service resolution. This enables DNS-SD and simple SRV service resolution, depending
        on the specified list of parameters (see above).</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--service-address=</option><replaceable>BOOL</replaceable></term>

        <listitem><para>Takes a boolean parameter. If true (the default), when doing a service lookup with
        <option>--service</option> the hostnames contained in the SRV resource records are resolved as well.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--service-txt=</option><replaceable>BOOL</replaceable></term>

        <listitem><para>Takes a boolean parameter. If true (the default), when doing a DNS-SD service lookup with
        <option>--service</option> the TXT service metadata record is resolved as well.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--openpgp</option></term>

        <listitem><para>Enables OPENPGPKEY resource record resolution (see above). Specified e-mail
        addresses are converted to the corresponding DNS domain name, and any OPENPGPKEY keys are
        printed.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--tlsa</option></term>

        <listitem><para>Enables TLSA resource record resolution (see above).
        A query will be performed for each of the specified names prefixed with
        the port and family
        (<literal>_<replaceable>port</replaceable>._<replaceable>family</replaceable>.<replaceable>domain</replaceable></literal>).
        The port number may be specified after a colon
        (<literal>:</literal>), otherwise <constant>443</constant> will be used
        by default. The family may be specified as an argument after
        <option>--tlsa</option>, otherwise <constant>tcp</constant> will be
        used.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--cname=</option><replaceable>BOOL</replaceable></term>

        <listitem><para>Takes a boolean parameter. If true (the default), DNS CNAME or DNAME redirections are
        followed. Otherwise, if a CNAME or DNAME record is encountered while resolving, an error is
        returned.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--search=</option><replaceable>BOOL</replaceable></term>

        <listitem><para>Takes a boolean parameter. If true (the default), any specified single-label hostnames will be
        searched in the domains configured in the search domain list, if it is non-empty. Otherwise, the search domain
        logic is disabled.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--raw</option><optional>=payload|packet</optional></term>

        <listitem><para>Dump the answer as binary data. If there is no argument or if the argument is
        <literal>payload</literal>, the payload of the packet is exported. If the argument is
        <literal>packet</literal>, the whole packet is dumped in wire format, prefixed by
        length specified as a little-endian 64-bit number. This format allows multiple packets
        to be dumped and unambiguously parsed.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--legend=</option><replaceable>BOOL</replaceable></term>

        <listitem><para>Takes a boolean parameter. If true (the default), column headers and meta information about the
        query response are shown. Otherwise, this output is suppressed.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--statistics</option></term>

        <listitem><para>If specified general resolver statistics are shown, including information whether DNSSEC is
        enabled and available, as well as resolution and validation statistics.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--reset-statistics</option></term>

        <listitem><para>Resets the statistics counters shown in <option>--statistics</option> to zero.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--flush-caches</option></term>

        <listitem><para>Flushes all DNS resource record caches the service maintains locally. This is mostly equivalent
        to sending the <constant>SIGUSR2</constant> to the <command>systemd-resolved</command>
        service.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--reset-server-features</option></term>

        <listitem><para>Flushes all feature level information the resolver learnt about specific servers, and ensures
        that the server feature probing logic is started from the beginning with the next look-up request. This is
        mostly equivalent to sending the <constant>SIGRTMIN+1</constant> to the <command>systemd-resolved</command>
        service.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--status</option></term>

        <listitem><para>Shows the global and per-link DNS settings in currently in effect.</para></listitem>
      </varlistentry>

      <xi:include href="standard-options.xml" xpointer="help" />
      <xi:include href="standard-options.xml" xpointer="version" />
      <xi:include href="standard-options.xml" xpointer="no-pager" />
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Retrieve the addresses of the <literal>www.0pointer.net</literal> domain</title>

      <programlisting>$ systemd-resolve www.0pointer.net
www.0pointer.net: 2a01:238:43ed:c300:10c3:bcf3:3266:da74
                  85.214.157.71

-- Information acquired via protocol DNS in 611.6ms.
-- Data is authenticated: no
</programlisting>
    </example>

    <example>
      <title>Retrieve the domain of the <literal>85.214.157.71</literal> IP address</title>

      <programlisting>$ systemd-resolve 85.214.157.71
85.214.157.71: gardel.0pointer.net

-- Information acquired via protocol DNS in 1.2997s.
-- Data is authenticated: no
</programlisting>
    </example>

    <example>
      <title>Retrieve the MX record of the <literal>yahoo.com</literal> domain</title>

      <programlisting>$ systemd-resolve -t MX yahoo.com --legend=no
yahoo.com. IN MX    1 mta7.am0.yahoodns.net
yahoo.com. IN MX    1 mta6.am0.yahoodns.net
yahoo.com. IN MX    1 mta5.am0.yahoodns.net
</programlisting>
    </example>

    <example>
      <title>Resolve an SRV service</title>

      <programlisting>$ systemd-resolve --service _xmpp-server._tcp gmail.com
_xmpp-server._tcp/gmail.com: alt1.xmpp-server.l.google.com:5269 [priority=20, weight=0]
                             173.194.210.125
                             alt4.xmpp-server.l.google.com:5269 [priority=20, weight=0]
                             173.194.65.125
                             …
</programlisting>
    </example>

    <example>
      <title>Retrieve a PGP key</title>

      <programlisting>$ systemd-resolve --openpgp zbyszek@fedoraproject.org
d08ee310438ca124a6149ea5cc21b6313b390dce485576eff96f8722._openpgpkey.fedoraproject.org. IN OPENPGPKEY
        mQINBFBHPMsBEACeInGYJCb+7TurKfb6wGyTottCDtiSJB310i37/6ZYoeIay/5soJjlMyf
        MFQ9T2XNT/0LM6gTa0MpC1st9LnzYTMsT6tzRly1D1UbVI6xw0g0vE5y2Cjk3xUwAynCsSs
        …
</programlisting>
    </example>

    <example>
      <title>Retrieve a TLS key (<literal>=tcp</literal> and
      <literal>:443</literal> could be skipped)</title>

      <programlisting>$ systemd-resolve --tlsa=tcp fedoraproject.org:443
_443._tcp.fedoraproject.org IN TLSA 0 0 1 19400be5b7a31fb733917700789d2f0a2471c0c9d506c0e504c06c16d7cb17c0
        -- Cert. usage: CA constraint
        -- Selector: Full Certificate
        -- Matching type: SHA-256
</programlisting>
    </example>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
  </refsect1>
</refentry>