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0c69794138
These lines are generally out-of-date, incomplete and unnecessary. With SPDX and git repository much more accurate and fine grained information about licensing and authorship is available, hence let's drop the per-file copyright notice. Of course, removing copyright lines of others is problematic, hence this commit only removes my own lines and leaves all others untouched. It might be nicer if sooner or later those could go away too, making git the only and accurate source of authorship information.
136 lines
5.2 KiB
XML
136 lines
5.2 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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SPDX-License-Identifier: LGPL-2.1+
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Copyright 2013 Tom Gundersen
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-->
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<refentry id="nss-myhostname" conditional='ENABLE_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 plug-in module for the GNU Name Service Switch (NSS) functionality of
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the GNU C Library (<command>glibc</command>), primarily providing hostname resolution for the locally configured
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system hostname as returned by
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<citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>. The precise
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hostnames resolved by this module are:</para>
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<itemizedlist>
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<listitem><para>The local, configured hostname is resolved to
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all locally configured IP addresses ordered by their scope, or
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— if none are configured — the IPv4 address 127.0.0.2 (which
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is on the local loopback) and the IPv6 address ::1 (which is the
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local host).</para></listitem>
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<listitem><para>The hostnames <literal>localhost</literal> and
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<literal>localhost.localdomain</literal> (as well as any hostname
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ending in <literal>.localhost</literal> or <literal>.localhost.localdomain</literal>)
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are resolved to the IP addresses 127.0.0.1 and ::1.</para></listitem>
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<listitem><para>The hostname <literal>_gateway</literal> is
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resolved to all current default routing gateway addresses,
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ordered by their metric. This assigns a stable hostname to the
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current gateway, useful for referencing it independently of the
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current network configuration state.</para></listitem>
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</itemizedlist>
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<para>Various software relies on an always-resolvable local
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hostname. When using dynamic hostnames, this is traditionally
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achieved by patching <filename>/etc/hosts</filename> at the same
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time as changing the hostname. This is problematic since it
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requires a writable <filename>/etc</filename> file system and is
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fragile because the file might be edited by the administrator at
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the same time. With <command>nss-myhostname</command> enabled,
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changing <filename>/etc/hosts</filename> is unnecessary, and on
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many systems, the file becomes entirely optional.</para>
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<para>To activate the NSS modules, add <literal>myhostname</literal> to the line starting with
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<literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>.</para>
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<para>It is recommended to place <literal>myhostname</literal> last in the <filename>nsswitch.conf</filename>'
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<literal>hosts:</literal> line to make sure that this mapping is only used as fallback, and that any DNS or
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<filename>/etc/hosts</filename> based mapping 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 is an example <filename>/etc/nsswitch.conf</filename> file that enables
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<command>nss-myhostname</command> correctly:</para>
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<programlisting>passwd: compat mymachines systemd
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group: compat mymachines systemd
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shadow: compat
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hosts: files mymachines resolve [!UNAVAIL=return] dns <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-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</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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