man/nss-myhostname.xml

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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">

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<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>
                <para><filename>nss-myhostname.la</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>)
                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 (which 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>