Adding upstream version 252.22.upstream/252.22upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 166 insertions, 0 deletions

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+<?xml version='1.0'?>
+<!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="nss-resolve" conditional='ENABLE_NSS_RESOLVE'>
+
+  <refentryinfo>
+    <title>nss-resolve</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>nss-resolve</refentrytitle>
+    <manvolnum>8</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>nss-resolve</refname>
+    <refname>libnss_resolve.so.2</refname>
+    <refpurpose>Hostname resolution via <filename>systemd-resolved.service</filename></refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <para><filename>libnss_resolve.so.2</filename></para>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para><command>nss-resolve</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of the
+    GNU C Library (<command>glibc</command>) enabling it to resolve hostnames via the
+    <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> local network
+    name resolution service. It replaces the <command>nss-dns</command> plug-in module that traditionally resolves
+    hostnames via DNS.</para>
+
+    <para>To activate the NSS module, add <literal>resolve [!UNAVAIL=return]</literal> to the line starting
+    with <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>. Specifically, it is
+    recommended to place <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'s
+    <literal>hosts:</literal> line. It should be before the <literal>files</literal> entry, since
+    <filename>systemd-resolved</filename> supports <filename>/etc/hosts</filename> internally, but with
+    caching. To the contrary, it should be after <literal>mymachines</literal>, to give hostnames given to
+    local VMs and containers precedence over names received over DNS. Finally, we recommend placing
+    <literal>dns</literal> somewhere after <literal>resolve</literal>, to fall back to
+    <command>nss-dns</command> if <filename>systemd-resolved.service</filename> is not available.</para>
+
+    <para>Note that <command>systemd-resolved</command> will synthesize DNS resource records in a few cases,
+    for example for <literal>localhost</literal> and the current local hostname, see
+    <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
+    the full list. This duplicates the functionality of
+    <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>, but
+    it is still recommended (see examples below) to keep <command>nss-myhostname</command> configured in
+    <filename>/etc/nsswitch.conf</filename>, to keep those names resolveable if
+    <command>systemd-resolved</command> is not running.</para>
+
+    <para>Please keep in mind that <command>nss-myhostname</command> (and <command>nss-resolve</command>) also resolve
+    in the other direction — from locally attached IP addresses to
+    hostnames. If you rely on that lookup being provided by DNS, you might
+    want to order things differently.
+    </para>
+
+    <para>Communication between <command>nss-resolve</command> and
+    <filename>systemd-resolved.service</filename> takes place via the
+    <filename>/run/systemd/resolve/io.systemd.Resolve</filename> <constant>AF_UNIX</constant> socket.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Environment variables</title>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$SYSTEMD_NSS_RESOLVE_VALIDATE</varname></term>
+
+        <listitem><para>Takes a boolean argument. When false, cryptographic validation of resource records
+        via DNSSEC will be disabled. This may be useful for testing, or when system time is known to be
+        unreliable.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$SYSTEMD_NSS_RESOLVE_SYNTHESIZE</varname></term>
+
+        <listitem><para>Takes a boolean argument. When false, synthetic records, e.g. for the local host
+        name, will not be returned. See section SYNTHETIC RECORDS in
+        <citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        for more information. This may be useful to query the "public" resource records, independent of the
+        configuration of the local machine.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$SYSTEMD_NSS_RESOLVE_CACHE</varname></term>
+
+        <listitem><para>Takes a boolean argument. When false, the cache of previously queried records will
+        not be used by <command>systemd-resolved</command>.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$SYSTEMD_NSS_RESOLVE_ZONE</varname></term>
+
+        <listitem><para>Takes a boolean argument. When false, answers using locally registered public
+        LLMNR/mDNS resource records will not be returned.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$SYSTEMD_NSS_RESOLVE_TRUST_ANCHOR</varname></term>
+
+        <listitem><para>Takes a boolean argument. When false, answers using locally configured trust anchors
+        will not be used.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$SYSTEMD_NSS_RESOLVE_NETWORK</varname></term>
+
+        <listitem><para>Takes a boolean argument. When false, answers will be returned without using the
+        network, i.e. either from local sources or the cache in <command>systemd-resolved</command>.
+        </para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Example</title>
+
+    <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
+    <command>nss-resolve</command> correctly:</para>
+
+    <!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
+<programlisting>passwd:         compat systemd
+group:          compat [SUCCESS=merge] systemd
+shadow:         compat systemd
+gshadow:        files systemd
+
+hosts:          mymachines <command>resolve [!UNAVAIL=return]</command> files myhostname dns
+networks:       files
+
+protocols:      db files
+services:       db files
+ethers:         db files
+rpc:            db files
+
+netgroup:       nis</programlisting>
+  </refsect1>
+
+  <refsect1>
+    <title>See Also</title>
+    <para>
+      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>