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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
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3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [ |
4 | <!ENTITY % entities SYSTEM "custom-entities.ent" > | |
5 | %entities; | |
6 | ]> | |
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7 | |
8 | <!-- | |
9 | This file is part of systemd. | |
10 | ||
11 | Copyright 2011 Lennart Poettering | |
12 | Copyright 2013 Tom Gundersen | |
13 | ||
14 | systemd is free software; you can redistribute it and/or modify it | |
15 | under the terms of the GNU Lesser General Public License as published by | |
16 | the Free Software Foundation; either version 2.1 of the License, or | |
17 | (at your option) any later version. | |
18 | ||
19 | systemd is distributed in the hope that it will be useful, but | |
20 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
21 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
22 | Lesser General Public License for more details. | |
23 | ||
24 | You should have received a copy of the GNU Lesser General Public License | |
25 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
26 | --> | |
27 | ||
56ba3c78 | 28 | <refentry id="nss-myhostname" conditional='HAVE_MYHOSTNAME'> |
16eb4da9 | 29 | |
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30 | <refentryinfo> |
31 | <title>nss-myhostname</title> | |
32 | <productname>systemd</productname> | |
33 | ||
34 | <authorgroup> | |
35 | <author> | |
36 | <contrib>Developer</contrib> | |
37 | <firstname>Lennart</firstname> | |
38 | <surname>Poettering</surname> | |
39 | <email>lennart@poettering.net</email> | |
40 | </author> | |
41 | </authorgroup> | |
42 | </refentryinfo> | |
43 | ||
44 | <refmeta> | |
45 | <refentrytitle>nss-myhostname</refentrytitle> | |
46 | <manvolnum>8</manvolnum> | |
47 | </refmeta> | |
48 | ||
49 | <refnamediv> | |
50 | <refname>nss-myhostname</refname> | |
51 | <refname>libnss_myhostname.so.2</refname> | |
52 | <refpurpose>Provide hostname resolution for the locally | |
53 | configured system hostname.</refpurpose> | |
54 | </refnamediv> | |
55 | ||
56 | <refsynopsisdiv> | |
57 | <para><filename>libnss_myhostname.so.2</filename></para> | |
58 | </refsynopsisdiv> | |
59 | ||
60 | <refsect1> | |
61 | <title>Description</title> | |
62 | ||
63 | <para><command>nss-myhostname</command> is a plugin for the GNU | |
64 | Name Service Switch (NSS) functionality of the GNU C Library | |
65 | (<command>glibc</command>) primarily providing hostname resolution | |
66 | for the locally configured system hostname as returned by | |
67 | <citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>. | |
68 | The precise hostnames resolved by this module are:</para> | |
69 | ||
70 | <itemizedlist> | |
71 | <listitem><para>The local, configured hostname is resolved to | |
72 | all locally configured IP addresses ordered by their scope, or | |
73 | — if none are configured — the IPv4 address 127.0.0.2 (which | |
74 | is on the local loopback) and the IPv6 address ::1 (which is the | |
75 | local host).</para></listitem> | |
76 | ||
77 | <listitem><para>The hostname <literal>localhost</literal> is | |
78 | resolved to the IP addresses 127.0.0.1 and | |
79 | ::1.</para></listitem> | |
80 | ||
81 | <listitem><para>The hostname <literal>gateway</literal> is | |
82 | resolved to all current default routing gateway addresses, | |
83 | ordered by their metric. This assigns a stable hostname to the | |
84 | current gateway, useful for referencing it independently of the | |
85 | current network configuration state.</para></listitem> | |
86 | ||
87 | </itemizedlist> | |
88 | ||
89 | <para>Various software relies on an always-resolvable local | |
90 | hostname. When using dynamic hostnames, this is traditionally | |
91 | achieved by patching <filename>/etc/hosts</filename> at the same | |
92 | time as changing the hostname. This is problematic since it | |
93 | requires a writable <filename>/etc</filename> file system and is | |
94 | fragile because the file might be edited by the administrator at | |
95 | the same time. With <command>nss-myhostname</command> enabled | |
ff9b60f3 | 96 | changing <filename>/etc/hosts</filename> is unnecessary, and on |
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97 | many systems the file becomes entirely optional.</para> |
98 | ||
99 | <para>To activate the NSS modules, <literal>myhostname</literal> | |
100 | has to be added to the line starting with | |
101 | <literal>hosts:</literal> in | |
102 | <filename>/etc/nsswitch.conf</filename>.</para> | |
103 | ||
104 | <para>It is recommended to place <literal>myhostname</literal> | |
105 | last in the <filename>nsswitch.conf</filename> line to make sure | |
106 | that this mapping is only used as fallback, and any DNS or | |
107 | <filename>/etc/hosts</filename> based mapping takes | |
108 | precedence.</para> | |
109 | </refsect1> | |
110 | ||
111 | <refsect1> | |
112 | <title>Example</title> | |
113 | ||
114 | <para>Here's an example <filename>/etc/nsswitch.conf</filename> | |
115 | file, that enables <command>myhostname</command> correctly:</para> | |
116 | ||
117 | <programlisting>passwd: compat | |
118 | group: compat | |
119 | shadow: compat | |
120 | ||
121 | hosts: files dns mymachines <command>myhostname</command> | |
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122 | networks: files |
123 | ||
124 | protocols: db files | |
125 | services: db files | |
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126 | ethers: db files |
127 | rpc: db files | |
16eb4da9 | 128 | |
9fccdb0f | 129 | netgroup: nis</programlisting> |
16eb4da9 | 130 | |
798d3a52 | 131 | <para>To test, use <command>glibc</command>'s <command>getent</command> tool:</para> |
16eb4da9 | 132 | |
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133 | <programlisting>$ getent ahosts `hostname` |
134 | ::1 STREAM omega | |
135 | ::1 DGRAM | |
136 | ::1 RAW | |
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137 | 127.0.0.2 STREAM |
138 | 127.0.0.2 DGRAM | |
9fccdb0f | 139 | 127.0.0.2 RAW</programlisting> |
16eb4da9 | 140 | |
798d3a52 | 141 | <para>In this case the local hostname is <varname>omega</varname>.</para> |
16eb4da9 | 142 | |
798d3a52 | 143 | </refsect1> |
16eb4da9 | 144 | |
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145 | <refsect1> |
146 | <title>See Also</title> | |
147 | <para> | |
148 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
149 | <citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>, | |
150 | <citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
151 | <citerefentry project='man-pages'><refentrytitle>getent</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
152 | </para> | |
153 | </refsect1> | |
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154 | |
155 | </refentry> |