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02e9308751
Let's replace the "compat" module in our proposed nsswitch.conf configuration with "files", since it is not 1995 anymore. Fedora and other distros have deprecated and removed NIS support a while back. While others still retain some support I am not sure we should advertise it in our examples. Downstream can of course still use "compat" instead of "files" if they want to, but let's not confuse people who don't care about NIS anymore with this. Also, bring the nsswitch.conf snippet in README in line with what our man pages say. Also see: https://fedoraproject.org/wiki/Changes/retire_NIS_user_space_utils
183 lines
8.0 KiB
XML
183 lines
8.0 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="nss-resolve" conditional='ENABLE_NSS_RESOLVE'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>nss-resolve</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>nss-resolve</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>nss-resolve</refname>
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<refname>libnss_resolve.so.2</refname>
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<refpurpose>Hostname resolution via <filename>systemd-resolved.service</filename></refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>libnss_resolve.so.2</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>nss-resolve</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of the
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GNU C Library (<command>glibc</command>) enabling it to resolve hostnames via the
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<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> local network
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name resolution service. It replaces the <command>nss-dns</command> plug-in module that traditionally resolves
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hostnames via DNS.</para>
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<para>To activate the NSS module, add <literal>resolve [!UNAVAIL=return]</literal> to the line starting
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with <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>. Specifically, it is
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recommended to place <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'s
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<literal>hosts:</literal> line. It should be before the <literal>files</literal> entry, since
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<filename>systemd-resolved</filename> supports <filename>/etc/hosts</filename> internally, but with
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caching. To the contrary, it should be after <literal>mymachines</literal>, to give hostnames given to
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local VMs and containers precedence over names received over DNS. Finally, we recommend placing
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<literal>dns</literal> somewhere after <literal>resolve</literal>, to fall back to
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<command>nss-dns</command> if <filename>systemd-resolved.service</filename> is not available.</para>
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<para>Note that <command>systemd-resolved</command> will synthesize DNS resource records in a few cases,
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for example for <literal>localhost</literal> and the current local hostname, see
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<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
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the full list. This duplicates the functionality of
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<citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>, but
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it is still recommended (see examples below) to keep <command>nss-myhostname</command> configured in
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<filename>/etc/nsswitch.conf</filename>, to keep those names resolveable if
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<command>systemd-resolved</command> is not running.</para>
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<para>Please keep in mind that <command>nss-myhostname</command> (and <command>nss-resolve</command>) also resolve
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in the other direction — from locally attached IP addresses to
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hostnames. If you rely on that lookup being provided by DNS, you might
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want to order things differently.
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</para>
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<para>Communication between <command>nss-resolve</command> and
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<filename>systemd-resolved.service</filename> takes place via the
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<filename>/run/systemd/resolve/io.systemd.Resolve</filename> <constant>AF_UNIX</constant> socket.</para>
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</refsect1>
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<refsect1>
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<title>Environment variables</title>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$SYSTEMD_NSS_RESOLVE_VALIDATE</varname></term>
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<listitem><para>Takes a boolean argument. When false, cryptographic validation of resource records
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via DNSSEC will be disabled. This may be useful for testing, or when system time is known to be
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unreliable.</para>
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<xi:include href="version-info.xml" xpointer="v250"/></listitem>
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</varlistentry>
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</variablelist>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$SYSTEMD_NSS_RESOLVE_SYNTHESIZE</varname></term>
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<listitem><para>Takes a boolean argument. When false, synthetic records, e.g. for the local host
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name, will not be returned. See section SYNTHETIC RECORDS in
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<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for more information. This may be useful to query the "public" resource records, independent of the
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configuration of the local machine.</para>
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<xi:include href="version-info.xml" xpointer="v250"/></listitem>
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</varlistentry>
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</variablelist>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$SYSTEMD_NSS_RESOLVE_CACHE</varname></term>
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<listitem><para>Takes a boolean argument. When false, the cache of previously queried records will
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not be used by
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<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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</para>
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<xi:include href="version-info.xml" xpointer="v250"/></listitem>
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</varlistentry>
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</variablelist>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$SYSTEMD_NSS_RESOLVE_ZONE</varname></term>
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<listitem><para>Takes a boolean argument. When false, answers using locally registered public
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LLMNR/mDNS resource records will not be returned.</para>
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<xi:include href="version-info.xml" xpointer="v250"/></listitem>
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</varlistentry>
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</variablelist>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$SYSTEMD_NSS_RESOLVE_TRUST_ANCHOR</varname></term>
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<listitem><para>Takes a boolean argument. When false, answers using locally configured trust anchors
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will not be used.</para>
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<xi:include href="version-info.xml" xpointer="v250"/></listitem>
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</varlistentry>
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</variablelist>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$SYSTEMD_NSS_RESOLVE_NETWORK</varname></term>
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<listitem><para>Takes a boolean argument. When false, answers will be returned without using the
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network, i.e. either from local sources or the cache in
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<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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</para>
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<xi:include href="version-info.xml" xpointer="v250"/></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
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<command>nss-resolve</command> correctly:</para>
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<!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
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<programlisting>passwd: files systemd
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group: files [SUCCESS=merge] systemd
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shadow: files systemd
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gshadow: files systemd
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hosts: mymachines <command>resolve [!UNAVAIL=return]</command> files myhostname dns
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networks: files
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protocols: db files
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services: db files
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ethers: db files
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rpc: db files
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netgroup: nis</programlisting>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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