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 Copyright © 2013 Tom Gundersen
11 <refentry id=
"nss-myhostname" conditional='ENABLE_MYHOSTNAME'
>
14 <title>nss-myhostname
</title>
15 <productname>systemd
</productname>
19 <contrib>Developer
</contrib>
20 <firstname>Lennart
</firstname>
21 <surname>Poettering
</surname>
22 <email>lennart@poettering.net
</email>
28 <refentrytitle>nss-myhostname
</refentrytitle>
29 <manvolnum>8</manvolnum>
33 <refname>nss-myhostname
</refname>
34 <refname>libnss_myhostname.so
.2</refname>
35 <refpurpose>Provide hostname resolution for the locally
36 configured system hostname.
</refpurpose>
40 <para><filename>libnss_myhostname.so
.2</filename></para>
44 <title>Description
</title>
46 <para><command>nss-myhostname
</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of
47 the GNU C Library (
<command>glibc
</command>), primarily providing hostname resolution for the locally configured
48 system hostname as returned by
49 <citerefentry><refentrytitle>gethostname
</refentrytitle><manvolnum>2</manvolnum></citerefentry>. The precise
50 hostnames resolved by this module are:
</para>
53 <listitem><para>The local, configured hostname is resolved to
54 all locally configured IP addresses ordered by their scope, or
55 — if none are configured — the IPv4 address
127.0.0.2 (which
56 is on the local loopback) and the IPv6 address ::
1 (which is the
57 local host).
</para></listitem>
59 <listitem><para>The hostnames
<literal>localhost
</literal> and
60 <literal>localhost.localdomain
</literal> (as well as any hostname
61 ending in
<literal>.localhost
</literal> or
<literal>.localhost.localdomain
</literal>)
62 are resolved to the IP addresses
127.0.0.1 and ::
1.
</para></listitem>
64 <listitem><para>The hostname
<literal>_gateway
</literal> is
65 resolved to all current default routing gateway addresses,
66 ordered by their metric. This assigns a stable hostname to the
67 current gateway, useful for referencing it independently of the
68 current network configuration state.
</para></listitem>
71 <para>Various software relies on an always-resolvable local
72 hostname. When using dynamic hostnames, this is traditionally
73 achieved by patching
<filename>/etc/hosts
</filename> at the same
74 time as changing the hostname. This is problematic since it
75 requires a writable
<filename>/etc
</filename> file system and is
76 fragile because the file might be edited by the administrator at
77 the same time. With
<command>nss-myhostname
</command> enabled,
78 changing
<filename>/etc/hosts
</filename> is unnecessary, and on
79 many systems, the file becomes entirely optional.
</para>
81 <para>To activate the NSS modules, add
<literal>myhostname
</literal> to the line starting with
82 <literal>hosts:
</literal> in
<filename>/etc/nsswitch.conf
</filename>.
</para>
84 <para>It is recommended to place
<literal>myhostname
</literal> last in the
<filename>nsswitch.conf
</filename>'
85 <literal>hosts:
</literal> line to make sure that this mapping is only used as fallback, and that any DNS or
86 <filename>/etc/hosts
</filename> based mapping takes precedence.
</para>
90 <title>Example
</title>
92 <para>Here is an example
<filename>/etc/nsswitch.conf
</filename> file that enables
93 <command>nss-myhostname
</command> correctly:
</para>
95 <programlisting>passwd: compat mymachines systemd
96 group: compat mymachines systemd
99 hosts: files mymachines resolve [!UNAVAIL=return] dns
<command>myhostname
</command>
107 netgroup: nis
</programlisting>
109 <para>To test, use
<command>glibc
</command>'s
<command>getent
</command> tool:
</para>
111 <programlisting>$ getent ahosts `hostname`
117 127.0.0.2 RAW
</programlisting>
119 <para>In this case, the local hostname is
<varname>omega
</varname>.
</para>
124 <title>See Also
</title>
126 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
127 <citerefentry><refentrytitle>nss-systemd
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
128 <citerefentry><refentrytitle>nss-resolve
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
129 <citerefentry><refentrytitle>nss-mymachines
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
130 <citerefentry project='man-pages'
><refentrytitle>nsswitch.conf
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
131 <citerefentry project='man-pages'
><refentrytitle>getent
</refentrytitle><manvolnum>1</manvolnum></citerefentry>