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| <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
| "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
| <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
| |
| <refentry id="systemd-resolved.service" conditional='ENABLE_RESOLVE'> |
| |
| <refentryinfo> |
| <title>systemd-resolved.service</title> |
| <productname>systemd</productname> |
| </refentryinfo> |
| |
| <refmeta> |
| <refentrytitle>systemd-resolved.service</refentrytitle> |
| <manvolnum>8</manvolnum> |
| </refmeta> |
| |
| <refnamediv> |
| <refname>systemd-resolved.service</refname> |
| <refname>systemd-resolved</refname> |
| <refpurpose>Network Name Resolution manager</refpurpose> |
| </refnamediv> |
| |
| <refsynopsisdiv> |
| <para><filename>systemd-resolved.service</filename></para> |
| <para><filename>/usr/lib/systemd/systemd-resolved</filename></para> |
| </refsynopsisdiv> |
| |
| <refsect1> |
| <title>Description</title> |
| |
| <para><command>systemd-resolved</command> is a system service that provides network name resolution to |
| local applications. It implements a caching and validating DNS/DNSSEC stub resolver, as well as an LLMNR |
| and MulticastDNS resolver and responder. Local applications may submit network name resolution requests |
| via three interfaces:</para> |
| |
| <itemizedlist> |
| <listitem><para>The native, fully-featured API <command>systemd-resolved</command> exposes on the bus, |
| see |
| <citerefentry><refentrytitle>org.freedesktop.resolve1</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| and |
| <citerefentry><refentrytitle>org.freedesktop.LogControl1</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| for details. Usage of this API is generally recommended to clients as it is asynchronous and fully |
| featured (for example, properly returns DNSSEC validation status and interface scope for addresses as |
| necessary for supporting link-local networking).</para></listitem> |
| |
| <listitem><para>The glibc |
| <citerefentry project='man-pages'><refentrytitle>getaddrinfo</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| API as defined by <ulink url="https://tools.ietf.org/html/rfc3493">RFC3493</ulink> and its related |
| resolver functions, including |
| <citerefentry project='man-pages'><refentrytitle>gethostbyname</refentrytitle><manvolnum>3</manvolnum></citerefentry>. |
| This API is widely supported, including beyond the Linux platform. In its current form it does not |
| expose DNSSEC validation status information however, and is synchronous only. This API is backed by the |
| glibc Name Service Switch |
| (<citerefentry project='man-pages'><refentrytitle>nss</refentrytitle><manvolnum>5</manvolnum></citerefentry>). |
| Usage of the glibc NSS module |
| <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry> is |
| required in order to allow glibc's NSS resolver functions to resolve hostnames via |
| <command>systemd-resolved</command>.</para></listitem> |
| |
| <listitem><para>Additionally, <command>systemd-resolved</command> provides a local DNS stub listener on |
| the IP addresses 127.0.0.53 and 127.0.0.54 on the local loopback interface. Programs issuing DNS |
| requests directly, bypassing any local API may be directed to this stub, in order to connect them to |
| <command>systemd-resolved</command>. Note however that it is strongly recommended that local programs |
| use the glibc NSS or bus APIs instead (as described above), as various network resolution concepts |
| (such as link-local addressing, or LLMNR Unicode domains) cannot be mapped to the unicast DNS |
| protocol.</para> |
| |
| <para id="proxy-stub">The DNS stub resolver on 127.0.0.53 provides the full feature set of the local |
| resolver, which includes offering LLMNR/MulticastDNS resolution. The DNS stub resolver on 127.0.0.54 |
| provides a more limited resolver, that operates in "proxy" mode only, i.e. it will pass most DNS |
| messages relatively unmodified to the current upstream DNS servers and back, but not try to process the |
| messages locally, and hence does not validate DNSSEC, or offer up LLMNR/MulticastDNS. (It will |
| translate to DNS-over-TLS communication if needed however.)</para></listitem> |
| </itemizedlist> |
| |
| <para>The DNS servers contacted are determined from the global settings in |
| <filename>/etc/systemd/resolved.conf</filename>, the per-link static settings in |
| <filename>/etc/systemd/network/*.network</filename> files (in case |
| <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| is used), the per-link dynamic settings received over DHCP, information provided via |
| <citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, and any |
| DNS server information made available by other system services. See |
| <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> and |
| <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> for |
| details about systemd's own configuration files for DNS servers. To improve compatibility, |
| <filename>/etc/resolv.conf</filename> is read in order to discover configured system DNS servers, but |
| only if it is not a symlink to <filename>/run/systemd/resolve/stub-resolv.conf</filename>, |
| <filename>/usr/lib/systemd/resolv.conf</filename> or |
| <filename>/run/systemd/resolve/resolv.conf</filename> (see below).</para> |
| |
| </refsect1> |
| |
| <refsect1> |
| <title>Synthetic Records</title> |
| |
| <para><command>systemd-resolved</command> synthesizes DNS resource records (RRs) for the following |
| cases:</para> |
| |
| <itemizedlist> |
| <listitem><para>The local, configured hostname is resolved to all locally configured IP addresses |
| ordered by their scope, or — if none are configured — the IPv4 address 127.0.0.2 (which is on the local |
| loopback interface) and the IPv6 address ::1 (which is the local host).</para></listitem> |
| |
| <listitem><para>The hostnames <literal>localhost</literal> and <literal>localhost.localdomain</literal> |
| as well as any hostname ending in <literal>.localhost</literal> or |
| <literal>.localhost.localdomain</literal> are resolved to the IP addresses 127.0.0.1 and ::1. |
| </para></listitem> |
| |
| <listitem><para>The hostname <literal>_gateway</literal> is resolved to all current default routing |
| gateway addresses, ordered by their metric. This assigns a stable hostname to the current gateway, |
| useful for referencing it independently of the current network configuration state.</para></listitem> |
| |
| <listitem><para>The hostname <literal>_outbound</literal> is resolved to the local IPv4 and IPv6 |
| addresses that are most likely used for communication with other hosts. This is determined by |
| requesting a routing decision to the configured default gateways from the kernel and then using the |
| local IP addresses selected by this decision. This hostname is only available if there is at least one |
| local default gateway configured. This assigns a stable hostname to the local outbound IP addresses, |
| useful for referencing them independently of the current network configuration state.</para></listitem> |
| |
| <listitem><para>The hostname <literal>_localdnsstub</literal> is resolved to the IP address 127.0.0.53, |
| i.e. the address the local DNS stub (see above) is listening on.</para></listitem> |
| |
| <listitem><para>The hostname <literal>_localdnsproxy</literal> is resolved to the IP address 127.0.0.54, |
| i.e. the address the local DNS proxy (see above) is listening on.</para></listitem> |
| |
| <listitem><para>The mappings defined in <filename>/etc/hosts</filename> are resolved to their |
| configured addresses and back, but they will not affect lookups for non-address types (like MX). |
| Support for <filename>/etc/hosts</filename> may be disabled with <varname>ReadEtcHosts=no</varname>, |
| see <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. |
| </para></listitem> |
| </itemizedlist> |
| </refsect1> |
| |
| <refsect1> |
| <title>Protocols and Routing</title> |
| |
| <para>The lookup requests that <filename>systemd-resolved.service</filename> receives are routed to the |
| available DNS servers, LLMNR, and MulticastDNS interfaces according to the following rules:</para> |
| |
| <itemizedlist> |
| <listitem><para>Names for which synthetic records are generated (the local hostname, |
| <literal>localhost</literal> and <literal>localdomain</literal>, local gateway, as listed in the |
| previous section) and addresses configured in <filename>/etc/hosts</filename> are never routed to the |
| network and a reply is sent immediately.</para></listitem> |
| |
| <listitem><para>Single-label names are resolved using LLMNR on all local interfaces where LLMNR is |
| enabled. Lookups for IPv4 addresses are only sent via LLMNR on IPv4, and lookups for IPv6 addresses are |
| only sent via LLMNR on IPv6. Note that lookups for single-label synthesized names are not routed to |
| LLMNR, MulticastDNS or unicast DNS.</para></listitem> |
| |
| <listitem><para>Queries for the address records (A and AAAA) of single-label non-synthesized names are |
| resolved via unicast DNS using search domains. For any interface which defines search domains, such |
| look-ups are routed to the servers defined for that interface, suffixed with each of those search |
| domains. When global search domains are defined, such look-ups are routed to the global servers. For |
| each search domain, queries are performed by suffixing the name with each of the search domains in |
| turn. Additionally, lookup of single-label names via unicast DNS may be enabled with the |
| <varname>ResolveUnicastSingleLabel=yes</varname> setting. The details of which servers are queried and |
| how the final reply is chosen are described below. Note that this means that address queries for |
| single-label names are never sent out to remote DNS servers by default, and resolution is only |
| possible if search domains are defined.</para></listitem> |
| |
| <listitem><para>Multi-label names with the domain suffix <literal>.local</literal> are resolved using |
| MulticastDNS on all local interfaces where MulticastDNS is enabled. As with LLMNR, IPv4 address lookups |
| are sent via IPv4 and IPv6 address lookups are sent via IPv6.</para></listitem> |
| |
| <listitem><para>Queries for multi-label names are routed via unicast DNS on local interfaces that have |
| a DNS server configured, plus the globally configured DNS servers if there are any. Which interfaces |
| are used is determined by the routing logic based on search and route-only domains, described below. |
| Note that by default, lookups for domains with the <literal>.local</literal> suffix are not routed to |
| DNS servers, unless the domain is specified explicitly as routing or search domain for the DNS server |
| and interface. This means that on networks where the <literal>.local</literal> domain is defined in a |
| site-specific DNS server, explicit search or routing domains need to be configured to make lookups work |
| within this DNS domain. Note that these days, it's generally recommended to avoid defining |
| <literal>.local</literal> in a DNS server, as <ulink |
| url="https://tools.ietf.org/html/rfc6762">RFC6762</ulink> reserves this domain for exclusive |
| MulticastDNS use.</para></listitem> |
| |
| <listitem><para>Address lookups (reverse lookups) are routed similarly to multi-label names, with the |
| exception that addresses from the link-local address range are never routed to unicast DNS and are only |
| resolved using LLMNR and MulticastDNS (when enabled).</para></listitem> |
| </itemizedlist> |
| |
| <para>If lookups are routed to multiple interfaces, the first successful response is returned (thus |
| effectively merging the lookup zones on all matching interfaces). If the lookup failed on all interfaces, |
| the last failing response is returned.</para> |
| |
| <para>Routing of lookups is determined by the per-interface routing domains (search and route-only) and |
| global search domains. See |
| <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> and |
| <citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for a |
| description how those settings are set dynamically and the discussion of <varname>Domains=</varname> in |
| <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a |
| description of globally configured DNS settings.</para> |
| |
| <para>The following query routing logic applies for unicast DNS lookups initiated by |
| <filename>systemd-resolved.service</filename>:</para> |
| |
| <itemizedlist> |
| <listitem><para>If a name to look up matches (that is: is equal to or has as suffix) any of the |
| configured routing domains (search or route-only) of any link, or the globally configured DNS settings, |
| "best matching" routing domain is determined: the matching one with the most labels. The query is then |
| sent to all DNS servers of any links or the globally configured DNS servers associated with this "best |
| matching" routing domain. (Note that more than one link might have this same "best matching" routing |
| domain configured, in which case the query is sent to all of them in parallel).</para> |
| |
| <para>In case of single-label names, when search domains are defined, the same logic applies, except |
| that the name is first suffixed by each of the search domains in turn. Note that this search logic |
| doesn't apply to any names with at least one dot. Also see the discussion about compatibility with |
| the traditional glibc resolver below.</para></listitem> |
| |
| <listitem><para>If a query does not match any configured routing domain (either per-link or global), it |
| is sent to all DNS servers that are configured on links with the <varname>DefaultRoute=</varname> |
| option set, as well as the globally configured DNS server.</para></listitem> |
| |
| <listitem><para>If there is no link configured as <varname>DefaultRoute=</varname> and no global DNS |
| server configured, one of the compiled-in fallback DNS servers is used.</para></listitem> |
| |
| <listitem><para>Otherwise the unicast DNS query fails, as no suitable DNS servers can be determined. |
| </para></listitem> |
| </itemizedlist> |
| |
| <para>The <varname>DefaultRoute=</varname> option is a boolean setting configurable with |
| <command>resolvectl</command> or in <filename>.network</filename> files. If not set, it is implicitly |
| determined based on the configured DNS domains for a link: if there's a route-only domain other than |
| <literal>~.</literal>, it defaults to false, otherwise to true.</para> |
| |
| <para>Effectively this means: in order to support single-label non-synthesized names, define appropriate |
| search domains. In order to preferably route all DNS queries not explicitly matched by routing domain |
| configuration to a specific link, configure a <literal>~.</literal> route-only domain on it. This will |
| ensure that other links will not be considered for these queries (unless they too carry such a routing |
| domain). In order to route all such DNS queries to a specific link only if no other link is preferred, |
| set the <varname>DefaultRoute=</varname> option for the link to true and do not configure a |
| <literal>~.</literal> route-only domain on it. Finally, in order to ensure that a specific link never |
| receives any DNS traffic not matching any of its configured routing domains, set the |
| <varname>DefaultRoute=</varname> option for it to false.</para> |
| |
| <para>See |
| <citerefentry><refentrytitle>org.freedesktop.resolve1</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| for information about the D-Bus APIs <filename>systemd-resolved</filename> provides.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Compatibility with the traditional glibc stub resolver</title> |
| |
| <para>This section provides a short summary of differences in the stub resolver implemented by |
| <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry> together |
| with <command>systemd-resolved</command> and the traditional stub resolver implemented in |
| <filename>nss-dns</filename>.</para> |
| |
| <itemizedlist> |
| <listitem><para>Some names are always resolved internally (see Synthetic Records above). Traditionally |
| they would be resolved by <filename>nss-files</filename> if provided in |
| <filename>/etc/hosts</filename>. But note that the details of how a query is constructed are under the |
| control of the client library. <filename>nss-dns</filename> will first try to resolve names using |
| search domains and even if those queries are routed to <filename>systemd-resolved</filename>, it will |
| send them out over the network using the usual rules for multi-label name routing <footnote><para>For |
| example, if <filename>/etc/resolv.conf</filename> has <programlisting>nameserver 127.0.0.53 |
| search foobar.com barbar.com |
| </programlisting>and we look up <literal>localhost</literal>, <filename>nss-dns</filename> will send |
| the following queries to <filename>systemd-resolved</filename> listening on 127.0.0.53:53: first |
| <literal>localhost.foobar.com</literal>, then <literal>localhost.barbar.com</literal>, and finally |
| <literal>localhost</literal>. If (hopefully) the first two queries fail, |
| <filename>systemd-resolved</filename> will synthesize an answer for the third query.</para> |
| |
| <para>When using <filename>nss-dns</filename> with any search domains, it is thus crucial to always |
| configure <filename>nss-files</filename> with higher priority and provide mappings for names that |
| should not be resolved using search domains.</para></footnote>.</para></listitem> |
| |
| <listitem><para>Single-label names are not resolved for A and AAAA records using unicast DNS (unless |
| overridden with <varname>ResolveUnicastSingleLabel=</varname>, see |
| <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>). |
| This is similar to the <option>no-tld-query</option> option being set in |
| <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. |
| </para></listitem> |
| |
| <listitem><para>Search domains are not used for <emphasis>suffixing</emphasis> of multi-label names. |
| (Search domains are nevertheless used for lookup <emphasis>routing</emphasis>, for names that were |
| originally specified as single-label or multi-label.) Any name with at least one dot is always |
| interpreted as a FQDN. <filename>nss-dns</filename> would resolve names both as relative (using search |
| domains) and absolute FQDN names. Some names would be resolved as relative first, and after that query |
| has failed, as absolute, while other names would be resolved in opposite order. The |
| <varname>ndots</varname> option in <filename>/etc/resolv.conf</filename> was used to control how many |
| dots the name needs to have to be resolved as relative first. This stub resolver does not implement |
| this at all: multi-label names are only resolved as FQDNs.<footnote><para>There are currently more than |
| 1500 top-level domain names defined, and new ones are added regularly, often using "attractive" names |
| that are also likely to be used locally. Not looking up multi-label names in this fashion avoids |
| fragility in both directions: a valid global name could be obscured by a local name, and resolution of |
| a relative local name could suddenly break when a new top-level domain is created, or when a new |
| subdomain of a top-level domain in registered. Resolving any given name as either relative or absolute |
| avoids this ambiguity.</para></footnote></para></listitem> |
| |
| <listitem><para>This resolver has a notion of the special <literal>.local</literal> domain used for |
| MulticastDNS, and will not route queries with that suffix to unicast DNS servers unless explicitly |
| configured, see above. Also, reverse lookups for link-local addresses are not sent to unicast DNS |
| servers.</para></listitem> |
| |
| <listitem><para>This resolver reads and caches <filename>/etc/hosts</filename> internally. (In other |
| words, <filename>nss-resolve</filename> replaces <filename>nss-files</filename> in addition to |
| <filename>nss-dns</filename>). Entries in <filename>/etc/hosts</filename> have highest priority.</para> |
| </listitem> |
| |
| <listitem><para>This resolver also implements LLMNR and MulticastDNS in addition to the classic unicast |
| DNS protocol, and will resolve single-label names using LLMNR (when enabled) and names ending in |
| <literal>.local</literal> using MulticastDNS (when enabled).</para></listitem> |
| |
| <listitem><para>Environment variables <varname>$LOCALDOMAIN</varname> and |
| <varname>$RES_OPTIONS</varname> described in |
| <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| are not supported currently.</para></listitem> |
| </itemizedlist> |
| </refsect1> |
| |
| <refsect1> |
| <title><filename>/etc/resolv.conf</filename></title> |
| |
| <para>Four modes of handling <filename>/etc/resolv.conf</filename> (see |
| <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>) are |
| supported:</para> |
| |
| <itemizedlist> |
| <listitem><para><command>systemd-resolved</command> maintains the |
| <filename>/run/systemd/resolve/stub-resolv.conf</filename> file for compatibility with traditional |
| Linux programs. This file lists the 127.0.0.53 DNS stub (see above) as the only DNS server. It also |
| contains a list of search domains that are in use by systemd-resolved. The list of search domains is |
| always kept up-to-date. Note that <filename>/run/systemd/resolve/stub-resolv.conf</filename> should not |
| be used directly by applications, but only through a symlink from |
| <filename>/etc/resolv.conf</filename>. This file may be symlinked from |
| <filename>/etc/resolv.conf</filename> in order to connect all local clients that bypass local DNS APIs |
| to <command>systemd-resolved</command> with correct search domains settings. This mode of operation is |
| recommended.</para></listitem> |
| |
| <listitem><para>A static file <filename>/usr/lib/systemd/resolv.conf</filename> is provided that lists |
| the 127.0.0.53 DNS stub (see above) as only DNS server. This file may be symlinked from |
| <filename>/etc/resolv.conf</filename> in order to connect all local clients that bypass local DNS APIs |
| to <command>systemd-resolved</command>. This file does not contain any search domains. |
| </para></listitem> |
| |
| <listitem><para><command>systemd-resolved</command> maintains the |
| <filename>/run/systemd/resolve/resolv.conf</filename> file for compatibility with traditional Linux |
| programs. This file may be symlinked from <filename>/etc/resolv.conf</filename> and is always kept |
| up-to-date, containing information about all known DNS servers. Note the file format's limitations: it |
| does not know a concept of per-interface DNS servers and hence only contains system-wide DNS server |
| definitions. Note that <filename>/run/systemd/resolve/resolv.conf</filename> should not be used |
| directly by applications, but only through a symlink from <filename>/etc/resolv.conf</filename>. If |
| this mode of operation is used local clients that bypass any local DNS API will also bypass |
| <command>systemd-resolved</command> and will talk directly to the known DNS servers.</para></listitem> |
| |
| <listitem><para>Alternatively, <filename>/etc/resolv.conf</filename> may be managed by other packages, |
| in which case <command>systemd-resolved</command> will read it for DNS configuration data. In this mode |
| of operation <command>systemd-resolved</command> is consumer rather than provider of this configuration |
| file. </para></listitem> |
| </itemizedlist> |
| |
| <para>Note that the selected mode of operation for this file is detected fully automatically, depending |
| on whether <filename>/etc/resolv.conf</filename> is a symlink to |
| <filename>/run/systemd/resolve/resolv.conf</filename> or lists 127.0.0.53 as DNS server.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Signals</title> |
| |
| <variablelist> |
| <varlistentry> |
| <term><constant>SIGUSR1</constant></term> |
| |
| <listitem><para>Upon reception of the <constant>SIGUSR1</constant> process signal |
| <command>systemd-resolved</command> will dump the contents of all DNS resource record caches it |
| maintains, as well as all feature level information it learnt about configured DNS servers into the |
| system logs.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><constant>SIGUSR2</constant></term> |
| |
| <listitem><para>Upon reception of the <constant>SIGUSR2</constant> process signal |
| <command>systemd-resolved</command> will flush all caches it maintains. Note that it should normally |
| not be necessary to request this explicitly – except for debugging purposes – as |
| <command>systemd-resolved</command> flushes the caches automatically anyway any time the host's |
| network configuration changes. Sending this signal to <command>systemd-resolved</command> is |
| equivalent to the <command>resolvectl flush-caches</command> command, however the latter is |
| recommended since it operates in a synchronous way.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><constant>SIGRTMIN+1</constant></term> |
| |
| <listitem><para>Upon reception of the <constant>SIGRTMIN+1</constant> process signal |
| <command>systemd-resolved</command> will forget everything it learnt about the configured DNS |
| servers. Specifically any information about server feature support is flushed out, and the server |
| feature probing logic is restarted on the next request, starting with the most fully featured |
| level. Note that it should normally not be necessary to request this explicitly – except for |
| debugging purposes – as <command>systemd-resolved</command> automatically forgets learnt information |
| any time the DNS server configuration changes. Sending this signal to |
| <command>systemd-resolved</command> is equivalent to the <command>resolvectl |
| reset-server-features</command> command, however the latter is recommended since it operates in a |
| synchronous way.</para></listitem> |
| </varlistentry> |
| </variablelist> |
| </refsect1> |
| |
| <refsect1> |
| <title>Credentials</title> |
| |
| <para><command>systemd-resolved</command> supports the service credentials logic as implemented by |
| <varname>LoadCredential=</varname>/<varname>SetCredential=</varname> (see |
| <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>1</manvolnum></citerefentry> for |
| details). The following credentials are used when passed in:</para> |
| |
| <variablelist> |
| <varlistentry> |
| <term><varname>network.dns</varname></term> |
| <term><varname>network.search_domains</varname></term> |
| |
| <listitem><para>May contain a space separated list of DNS server IP addresses and DNS search |
| domains. This information is only used when no explicit configuration via |
| <filename>/etc/systemd/resolved.conf</filename>, <filename>/etc/resolv.conf</filename> or the kernel |
| command line has been provided.</para></listitem> |
| </varlistentry> |
| </variablelist> |
| </refsect1> |
| |
| <refsect1> |
| <title>Kernel Command Line</title> |
| |
| <para><command>systemd-resolved</command> also honours two kernel command line options:</para> |
| |
| <variablelist class='kernel-commandline-options'> |
| <varlistentry> |
| <term><varname>nameserver=</varname></term> |
| <term><varname>domain=</varname></term> |
| |
| <listitem><para>Takes the IP address of a DNS server (in case of <varname>nameserver=</varname>), and |
| a DNS search domain (in case of <varname>domain=</varname>). May be used multiple times, to define |
| multiple DNS servers/search domains. If either of these options are specified |
| <filename>/etc/resolv.conf</filename> will not be read and the <varname>DNS=</varname> and |
| <varname>Domains=</varname> settings of |
| <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| will be ignored. These two kernel command line options hence override system |
| configuration.</para></listitem> |
| </varlistentry> |
| </variablelist> |
| </refsect1> |
| |
| <refsect1> |
| <title>See Also</title> |
| <para> |
| <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>dnssec-trust-anchors.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>resolvectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
| <citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| <citerefentry project='man-pages'><refentrytitle>hosts</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| </para> |
| </refsect1> |
| |
| </refentry> |
