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