75555c2824
This unifies the suggested nsswitch.conf configuration for our four NSS modules to this:
hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
Note that this restores "myhostname" to the suggested configuration of
nss-resolve for the time being, undoing 4484e1792b.
"myhostname" should probably be dropped eventually, but when we do this we
should do it in full, and not only drop it from the suggested nsswitch.conf
for one of the modules, but also drop it in source and stop referring to it
altogether.
Note that nss-resolve doesn't replace nss-myhostname in full: the former only
works if D-Bus/resolved is available for resolving the local hostname, the
latter works in all cases even if D-Bus or resolved are not in operation, hence
there's some value in keeping the line as it is right now. Note that neither
dns nor myhostname are considered at all with the above configuration unless
the resolve module actually returns UNAVAIL. Thus, even though handling of
local hostname resolving is implemented twice this way it is only executed once
for each lookup.
150 lines
5.8 KiB
XML
150 lines
5.8 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 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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