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machined: optionally, allow registration of pre-existing units (scopes
[elogind.git] / man / nss-myhostname.xml
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">
4
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8   Copyright 2011 Lennart Poettering
9   Copyright 2013 Tom Gundersen
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24
25 <refentry id="nss-myhostname" conditional='HAVE_MYHOSTNAME'>
26
27         <refentryinfo>
28                 <title>nss-myhostname</title>
29                 <productname>systemd</productname>
30
31                 <authorgroup>
32                         <author>
33                                 <contrib>Developer</contrib>
34                                 <firstname>Lennart</firstname>
35                                 <surname>Poettering</surname>
36                                 <email>lennart@poettering.net</email>
37                         </author>
38                 </authorgroup>
39         </refentryinfo>
40
41         <refmeta>
42                 <refentrytitle>nss-myhostname</refentrytitle>
43                 <manvolnum>8</manvolnum>
44         </refmeta>
45
46         <refnamediv>
47                 <refname>nss-myhostname</refname>
48                 <refpurpose>Provide hostname resolution for the locally
49                 configured system hostname.</refpurpose>
50         </refnamediv>
51
52         <refsynopsisdiv>
53                 <para><filename>nss-myhostname.la</filename></para>
54         </refsynopsisdiv>
55
56         <refsect1>
57                 <title>Description</title>
58
59                 <para><command>nss-myhostname</command> is a plugin for the GNU Name Service Switch
60                 (NSS) functionality of the GNU C Library (<command>glibc</command>)
61                 providing hostname resolution for the locally configured system
62                 hostname as returned by
63                 <citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
64                 Various software relies on an always-resolvable local hostname. When
65                 using dynamic hostnames, this is usually achieved by patching
66                 <filename>/etc/hosts</filename> at the same time as changing the host
67                 name. This however is not ideal since it requires a writable
68                 <filename>/etc</filename> file system and is fragile because the file
69                 might be edited by the administrator at the same time. <command>nss-myhostname</command>
70                 simply returns all locally configured public IP addresses, or, if none
71                 are configured, the IPv4 address 127.0.0.2 (which is on the local
72                 loopback) and the IPv6 address ::1 (which is the local host) for
73                 whatever system hostname is configured locally. Patching
74                 <filename>/etc/hosts</filename> is thus no longer necessary.</para>
75
76                 <para>To activate the NSS modules, <option>myhostname</option>
77                 has to be added to the line starting with "<varname>hosts:</varname>" in
78                 <filename>/etc/nsswitch.conf</filename></para>
79
80                 <para>It is recommended to put <option>myhostname</option>
81                 last in the <filename>nsswitch.conf</filename> line to make
82                 sure that this mapping is only used as fallback, and any DNS
83                 or <filename>/etc/hosts</filename> based mapping takes precedence.</para>
84         </refsect1>
85
86         <refsect1>
87                 <title>Example</title>
88
89                 <programlisting>
90 # /etc/nsswitch.conf
91
92 passwd:         compat
93 group:          compat
94 shadow:         compat
95
96 hosts:          files dns <varname>myhostname</varname>
97 networks:       files
98
99 protocols:      db files
100 services:       db files
101 ethers:         db files
102 rpc:            db files
103
104 netgroup:       nis
105                 </programlisting>
106
107                 <para>To test, use <command>glibc</command>'s <command>getent</command> tool:</para>
108
109                 <programlisting>
110 $ getent ahosts `hostname`
111 ::1             STREAM omega
112 ::1             DGRAM
113 ::1             RAW
114 127.0.0.2       STREAM
115 127.0.0.2       DGRAM
116 127.0.0.2       RAW
117                 </programlisting>
118
119                 <para>In this case the local hostname is <varname>omega</varname>.</para>
120
121         </refsect1>
122
123         <refsect1>
124                 <title>See Also</title>
125                 <para>
126                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
127                         <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
128                         <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
129                         <citerefentry><refentrytitle>loginctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
130                         <citerefentry><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
131                         <citerefentry><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
132                         <citerefentry><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
133                         <citerefentry><refentrytitle>pam_loginuid</refentrytitle><manvolnum>8</manvolnum></citerefentry>
134                 </para>
135         </refsect1>
136
137 </refentry>