Adding upstream version 255.4.upstream/255.4

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

1 files changed, 139 insertions, 0 deletions

diff --git a/man/nss-myhostname.xml b/man/nss-myhostname.xml
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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!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-myhostname" conditional='ENABLE_NSS_MYHOSTNAME'>
+
+  <refentryinfo>
+    <title>nss-myhostname</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>nss-myhostname</refentrytitle>
+    <manvolnum>8</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>nss-myhostname</refname>
+    <refname>libnss_myhostname.so.2</refname>
+    <refpurpose>Hostname resolution for the locally configured system hostname</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <para><filename>libnss_myhostname.so.2</filename></para>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para><command>nss-myhostname</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of
+    the GNU C Library (<command>glibc</command>), primarily providing hostname resolution for the locally configured
+    system hostname as returned by
+    <citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>.  The precise
+    hostnames resolved by this module are:</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) 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>
+    </itemizedlist>
+
+    <para>Various software relies on an always-resolvable local
+    hostname. When using dynamic hostnames, this is traditionally
+    achieved by patching <filename>/etc/hosts</filename> at the same
+    time as changing the hostname. This is problematic since it
+    requires a writable <filename>/etc/</filename> file system and is
+    fragile because the file might be edited by the administrator at
+    the same time. With <command>nss-myhostname</command> enabled,
+    changing <filename>/etc/hosts</filename> is unnecessary, and on
+    many systems, the file becomes entirely optional.</para>
+
+    <para>To activate the NSS modules, add <literal>myhostname</literal> to the line starting with
+    <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>.</para>
+
+    <para>It is recommended to place <literal>myhostname</literal> after <literal>file</literal> and before <literal>dns</literal>.
+    This resolves well-known hostnames like <literal>localhost</literal>
+    and the machine hostnames locally. It is consistent with the behaviour
+    of <command>nss-resolve</command>, and still allows overriding via
+    <filename>/etc/hosts</filename>.</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>
+  </refsect1>
+
+  <refsect1>
+    <title>Example</title>
+
+    <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
+    <command>nss-myhostname</command> correctly:</para>
+
+    <!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
+<programlisting>passwd:         files systemd
+group:          files [SUCCESS=merge] systemd
+shadow:         files systemd
+gshadow:        files systemd
+
+hosts:          mymachines resolve [!UNAVAIL=return] files <command>myhostname</command> dns
+networks:       files
+
+protocols:      db files
+services:       db files
+ethers:         db files
+rpc:            db files
+
+netgroup:       nis</programlisting>
+
+    <para>To test, use <command>glibc</command>'s
+    <citerefentry project='man-pages'><refentrytitle>getent</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    tool:</para>
+
+    <programlisting>$ getent ahosts `hostname`
+::1       STREAM omega
+::1       DGRAM
+::1       RAW
+127.0.0.2       STREAM
+127.0.0.2       DGRAM
+127.0.0.2       RAW</programlisting>
+
+    <para>In this case, the local hostname is <varname>omega</varname>.</para>
+
+  </refsect1>
+
+  <refsect1>
+    <title>See Also</title>
+    <para>
+      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>nss-resolve</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 project='man-pages'><refentrytitle>getent</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>