164 lines
6.7 KiB
XML
164 lines
6.7 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2011 Lennart Poettering
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Copyright 2013 Tom Gundersen
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="nss-myhostname" conditional='HAVE_MYHOSTNAME'>
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<refentryinfo>
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<title>nss-myhostname</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>nss-myhostname</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>nss-myhostname</refname>
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<refname>libnss_myhostname.so.2</refname>
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<refpurpose>Provide hostname resolution for the locally
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configured system hostname.</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>libnss_myhostname.so.2</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>nss-myhostname</command> is a plugin
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for the GNU Name Service Switch (NSS) functionality of
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the GNU C Library (<command>glibc</command>) primarily
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providing hostname resolution for the locally
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configured system hostname as returned by
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<citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>. The
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precise hostnames resolved by this module are:</para>
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<itemizedlist>
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<listitem><para>The local, configured hostname
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is resolved to all locally configured IP
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addresses ordered by their scope, or -- if
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none are configured -- the IPv4 address
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127.0.0.2 (which is on the local loopback) and
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the IPv6 address ::1 (which is the local
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host).</para></listitem>
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<listitem><para>The hostname
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<literal>localhost</literal> is resolved to
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the IP addresses 127.0.0.1 and
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::1.</para></listitem>
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<listitem><para>The hostname
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<literal>gateway</literal> is resolved to all
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current default routing gateway addresses,
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ordered by their metric. This assigns a stable
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hostname to the current gateway, useful for
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referencing it independently of the current
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network configuration state.</para></listitem>
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</itemizedlist>
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<para>Various software relies on an always-resolvable
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local hostname. When using dynamic hostnames, this is
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traditionally achieved by patching
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<filename>/etc/hosts</filename> at the same time as
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changing the hostname. This is problematic since it
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requires a writable <filename>/etc</filename> file
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system and is fragile because the file might be edited
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by the administrator at the same time. With
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<command>nss-myhostname</command> enabled changing
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<filename>/etc/hosts</filename> is unncessary, and on
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many systems the file becomes entirely optional.</para>
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<para>To activate the NSS modules,
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<literal>myhostname</literal> has to be added to the
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line starting with <literal>hosts:</literal> in
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<filename>/etc/nsswitch.conf</filename>.</para>
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<para>It is recommended to place
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<literal>myhostname</literal> last in the
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<filename>nsswitch.conf</filename> line to make sure
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that this mapping is only used as fallback, and any
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DNS or <filename>/etc/hosts</filename> based mapping
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takes precedence.</para>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<para>Here's an example
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<filename>/etc/nsswitch.conf</filename> file, that
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enables <command>myhostname</command>
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correctly:</para>
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<programlisting>passwd: compat
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group: compat
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shadow: compat
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hosts: files dns mymachines <command>myhostname</command>
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networks: files
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protocols: db files
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services: db files
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ethers: db files
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rpc: db files
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netgroup: nis</programlisting>
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<para>To test, use <command>glibc</command>'s <command>getent</command> tool:</para>
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<programlisting>$ getent ahosts `hostname`
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::1 STREAM omega
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::1 DGRAM
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::1 RAW
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127.0.0.2 STREAM
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127.0.0.2 DGRAM
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127.0.0.2 RAW</programlisting>
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<para>In this case the local hostname is <varname>omega</varname>.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>getent</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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