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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<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>

<refpurpose>Provide host name resolution for the locally

configured system hostname.</refpurpose>

</refnamediv>

<refsynopsisdiv>

<cmdsynopsis>

<command>nss-myhostname.la</command>

</cmdsynopsis>

</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>)

providing host name resolution for the locally configured system

hostname as returned by

<citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>.

Various software relies on an always resolvable local host name. When

using dynamic hostnames this is usually achieved by patching

<filename>/etc/hosts</filename> at the same time as changing the host

name. This however is not ideal 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. <command>nss-myhostname</command>

simply returns all locally configure public IP addresses, or -- if none

are configured -- the IPv4 address 127.0.0.2 (wich is on the local

loopback) and the IPv6 address ::1 (which is the local host) for

whatever system hostname is configured locally. Patching

<filename>/etc/hosts</filename> is thus no longer necessary.</para>

<para>To activate the NSS modules, <option>myhostname</option>

has to be added to the line starting with "<varname>hosts:</varname>" in

<filename>/etc/nsswitch.conf</filename></para>

<para>It is recommended to put <option>myhostname</option>

last in the <filename>nsswitch.conf</filename> line to make

sure that this mapping is only used as fallback, and any DNS

or <filename>/etc/hosts</filename> based mapping takes precedence.</para>

</refsect1>

<refsect1>

<title>Example</title>

<programlisting>

# /etc/nsswitch.conf

passwd: compat

group: compat

shadow: compat

hosts: files dns <varname>myhostname</varname>

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 host name is <varname>omega</varname>.</para>

</refsect1>

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>loginctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,

<citerefentry><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

<citerefentry><refentrytitle>pam_loginuid</refentrytitle><manvolnum>8</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>