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man: rework nss-myhostname man page

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Remove a number of incorrect links, and explain that "localhost" and
"gateway" are now resolved by it, too.
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Lennart Poettering 2015-01-07 17:14:04 +01:00
parent 5b728e6ba1
commit b311d32ff4
1 changed files with 61 additions and 34 deletions
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95
man/nss-myhostname.xml
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@ -50,49 +50,81 @@
</refnamediv>
<refsynopsisdiv>
<para><filename>nss-myhostname.la</filename></para>
<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>)
providing hostname 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 hostname. 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 configured 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><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>
<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>
<itemizedlist>
<listitem><para>The local, configured hostname
is resolved to all locally configured 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).</para></listitem>
<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>
<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 unncessary, 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 any
DNS or <filename>/etc/hosts</filename> based mapping
takes precedence.</para>
</refsect1>
<refsect1>
<title>Example</title>
<programlisting># /etc/nsswitch.conf
<para>Here's an example
<filename>/etc/nsswitch.conf</filename> file, that
enables <command>myhostname</command>
correctly:</para>
passwd: compat
<programlisting>passwd: compat
group: compat
shadow: compat
hosts: files dns <varname>myhostname</varname>
hosts: files dns <command>myhostname</command>
networks: files
protocols: db files
@ -120,13 +152,8 @@ netgroup: nis</programlisting>
<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 project='man-pages'><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>pam_loginuid</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>