1 <?xml version='
1.0'
?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
6 SPDX-License-Identifier: LGPL-2.1+
8 This file is part of systemd.
10 Copyright 2011 Lennart Poettering
11 Copyright 2013 Tom Gundersen
13 systemd is free software; you can redistribute it and/or modify it
14 under the terms of the GNU Lesser General Public License as published by
15 the Free Software Foundation; either version 2.1 of the License, or
16 (at your option) any later version.
18 systemd is distributed in the hope that it will be useful, but
19 WITHOUT ANY WARRANTY; without even the implied warranty of
20 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
21 Lesser General Public License for more details.
23 You should have received a copy of the GNU Lesser General Public License
24 along with systemd; If not, see <http://www.gnu.org/licenses/>.
27 <refentry id=
"nss-myhostname" conditional='ENABLE_MYHOSTNAME'
>
30 <title>nss-myhostname
</title>
31 <productname>systemd
</productname>
35 <contrib>Developer
</contrib>
36 <firstname>Lennart
</firstname>
37 <surname>Poettering
</surname>
38 <email>lennart@poettering.net
</email>
44 <refentrytitle>nss-myhostname
</refentrytitle>
45 <manvolnum>8</manvolnum>
49 <refname>nss-myhostname
</refname>
50 <refname>libnss_myhostname.so
.2</refname>
51 <refpurpose>Provide hostname resolution for the locally
52 configured system hostname.
</refpurpose>
56 <para><filename>libnss_myhostname.so
.2</filename></para>
60 <title>Description
</title>
62 <para><command>nss-myhostname
</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of
63 the GNU C Library (
<command>glibc
</command>), primarily providing hostname resolution for the locally configured
64 system hostname as returned by
65 <citerefentry><refentrytitle>gethostname
</refentrytitle><manvolnum>2</manvolnum></citerefentry>. The precise
66 hostnames resolved by this module are:
</para>
69 <listitem><para>The local, configured hostname is resolved to
70 all locally configured IP addresses ordered by their scope, or
71 — if none are configured — the IPv4 address
127.0.0.2 (which
72 is on the local loopback) and the IPv6 address ::
1 (which is the
73 local host).
</para></listitem>
75 <listitem><para>The hostnames
<literal>localhost
</literal> and
76 <literal>localhost.localdomain
</literal> (as well as any hostname
77 ending in
<literal>.localhost
</literal> or
<literal>.localhost.localdomain
</literal>)
78 are resolved to the IP addresses
127.0.0.1 and ::
1.
</para></listitem>
80 <listitem><para>The hostname
<literal>_gateway
</literal> is
81 resolved to all current default routing gateway addresses,
82 ordered by their metric. This assigns a stable hostname to the
83 current gateway, useful for referencing it independently of the
84 current network configuration state.
</para></listitem>
87 <para>Various software relies on an always-resolvable local
88 hostname. When using dynamic hostnames, this is traditionally
89 achieved by patching
<filename>/etc/hosts
</filename> at the same
90 time as changing the hostname. This is problematic since it
91 requires a writable
<filename>/etc
</filename> file system and is
92 fragile because the file might be edited by the administrator at
93 the same time. With
<command>nss-myhostname
</command> enabled,
94 changing
<filename>/etc/hosts
</filename> is unnecessary, and on
95 many systems, the file becomes entirely optional.
</para>
97 <para>To activate the NSS modules, add
<literal>myhostname
</literal> to the line starting with
98 <literal>hosts:
</literal> in
<filename>/etc/nsswitch.conf
</filename>.
</para>
100 <para>It is recommended to place
<literal>myhostname
</literal> last in the
<filename>nsswitch.conf
</filename>'
101 <literal>hosts:
</literal> line to make sure that this mapping is only used as fallback, and that any DNS or
102 <filename>/etc/hosts
</filename> based mapping takes precedence.
</para>
106 <title>Example
</title>
108 <para>Here is an example
<filename>/etc/nsswitch.conf
</filename> file that enables
109 <command>nss-myhostname
</command> correctly:
</para>
111 <programlisting>passwd: compat mymachines systemd
112 group: compat mymachines systemd
115 hosts: files mymachines resolve [!UNAVAIL=return] dns
<command>myhostname
</command>
123 netgroup: nis
</programlisting>
125 <para>To test, use
<command>glibc
</command>'s
<command>getent
</command> tool:
</para>
127 <programlisting>$ getent ahosts `hostname`
133 127.0.0.2 RAW
</programlisting>
135 <para>In this case, the local hostname is
<varname>omega
</varname>.
</para>
140 <title>See Also
</title>
142 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
143 <citerefentry><refentrytitle>nss-systemd
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
144 <citerefentry><refentrytitle>nss-resolve
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
145 <citerefentry><refentrytitle>nss-mymachines
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
146 <citerefentry project='man-pages'
><refentrytitle>nsswitch.conf
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
147 <citerefentry project='man-pages'
><refentrytitle>getent
</refentrytitle><manvolnum>1</manvolnum></citerefentry>