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man: change recommended order of NSS modules in /etc/nsswitch.conf

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So far we recommended placing "nss-mymachines" after "nss-resolve" in the order
of preference in /etc/nsswitch.conf. This change reverse this order.

Rationale: single-label names are resolved via LLMNR by resolved, which has to
time out if no peer by that name exists. By placing "nss-mymachines" first
(which always responds immediately) we avoid running into this timeout for most
containers. Both modules should return the same data if LLMNR is used by the
container anyway.

While we are at it, improve the man pages of the three NSS modules in other
ways a bit.
This commit is contained in:
Lennart Poettering 2016-02-23 18:24:03 +01:00
parent 45bd485454
commit 9053aaad42
3 changed files with 47 additions and 65 deletions
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32
man/nss-myhostname.xml
View File

@ -57,12 +57,11 @@
<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>
<para><command>nss-myhostname</command> is a plug-in module 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
@ -80,7 +79,6 @@
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
@ -93,29 +91,25 @@
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>To activate the NSS modules, add <literal>myhostname</literal> 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>
<para>It is recommended to place <literal>myhostname</literal> last in the <filename>nsswitch.conf</filename>'
<literal>hosts:</literal> 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>
<para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
<command>nss-myhostname</command> correctly:</para>
<programlisting>passwd: compat mymachines
group: compat mymachines
shadow: compat
hosts: files resolve mymachines <command>myhostname</command>
hosts: files mymachines resolve <command>myhostname</command>
networks: files
protocols: db files

39
man/nss-mymachines.xml
View File

@ -56,42 +56,37 @@
<refsect1>
<title>Description</title>
<para><command>nss-mymachines</command> is a plugin for the GNU
Name Service Switch (NSS) functionality of the GNU C Library
(<command>glibc</command>), providing hostname resolution for
container names of containers running locally that are registered
with
<citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
The container names are resolved to the IP addresses of the
specific container, ordered by their scope.</para>
<para><command>nss-mymachines</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of
the GNU C Library (<command>glibc</command>), providing hostname resolution for the names of containers running
locally that are registered with
<citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>. The
container names are resolved to the IP addresses of the specific container, ordered by their scope. This
functionality only applies to containers using network namespacing.</para>
<para>The module also resolves user IDs used by containers to user
names indicating the container name, and back.</para>
<para>The module also resolves user and group IDs used by containers to user and group names indicating the
container name, and back. This functionality only applies to containers using user namespacing.</para>
<para>To activate the NSS modules, <literal>mymachines</literal>
has to be added to the lines starting with
<literal>hosts:</literal>, <literal>passwd:</literal> and
<literal>group:</literal> in
<para>To activate the NSS module, add <literal>mymachines</literal> to the lines starting with
<literal>hosts:</literal>, <literal>passwd:</literal> and <literal>group:</literal> in
<filename>/etc/nsswitch.conf</filename>.</para>
<para>It is recommended to place <literal>mymachines</literal>
near the end of the <filename>nsswitch.conf</filename> lines to
make sure that its mappings are only used as fallback, and that any
other mappings, such as DNS or <filename>/etc/hosts</filename>
based mappings, take precedence.</para>
<para>It is recommended to place <literal>mymachines</literal> after the <literal>files</literal> or
<literal>compat</literal> entry of the <filename>/etc/nsswitch.conf</filename> lines to make sure that its mappings
are preferred over other resolvers such as DNS, but so that <filename>/etc/hosts</filename>,
<filename>/etc/passwd</filename> and <filename>/etc/group</filename> based mappings take precedence.</para>
</refsect1>
<refsect1>
<title>Example</title>
<para>Here is an example <filename>/etc/nsswitch.conf</filename>
file that enables <command>mymachines</command> correctly:</para>
<para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
<command>nss-mymachines</command> correctly:</para>
<programlisting>passwd: compat <command>mymachines</command>
group: compat <command>mymachines</command>
shadow: compat
hosts: files resolve <command>mymachines</command> myhostname
hosts: files <command>mymachines</command> resolve myhostname
networks: files
protocols: db files

41
man/nss-resolve.xml
View File

@ -56,37 +56,36 @@
<refsect1>
<title>Description</title>
<para><command>nss-resolve</command> is a plugin module for the
GNU Name Service Switch (NSS) functionality of the GNU C Library
(<command>glibc</command>) enabling it to resolve host names via
the
<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>
local network name resolution service.</para>
<para><command>nss-resolve</command> is a plug-in module for the GNU Name Service Switch (NSS) functionality of the
GNU C Library (<command>glibc</command>) enabling it to resolve host names via the
<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry> local network
name resolution service. It replaces the <command>nss-dns</command> plug-in module that traditionally resolves
hostnames via DNS.</para>
<para>To activate the NSS module, <literal>resolve</literal>
has to be added to the line starting with
<literal>hosts:</literal> in
<filename>/etc/nsswitch.conf</filename>.</para>
<para>To activate the NSS module, add <literal>resolve</literal> to the line starting with
<literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>.</para>
<para>It is recommended to place <literal>resolve</literal> early
in the <filename>nsswitch.conf</filename> line (but after the
<literal>files</literal> entry), replacing the
<literal>dns</literal> entry if it exists, to ensure DNS queries
are always routed via
<para>It is recommended to place <literal>resolve</literal> early in <filename>/etc/nsswitch.conf</filename>'
<literal>hosts:</literal> line (but after the <literal>files</literal> or <literal>mymachines</literal> entries),
replacing the <literal>dns</literal> entry if it exists, to ensure DNS queries are always routed via
<citerefentry><refentrytitle>systemd-resolved</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
<para>Note that <command>nss-resolve</command> will chain-load <command>nss-dns</command> if
<filename>systemd-resolved.service</filename> is not running, ensuring that basic DNS resolution continues to work
if the service is down.</para>
</refsect1>
<refsect1>
<title>Example</title>
<para>Here is an example <filename>/etc/nsswitch.conf</filename>
file that enables <command>resolve</command> correctly:</para>
<para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables <command>nss-resolve</command>
correctly:</para>
<programlisting>passwd: compat mymachines
group: compat mymachines
shadow: compat
hosts: files <command>resolve</command> mymachines myhostname
hosts: files mymachines <command>resolve</command> myhostname
networks: files
protocols: db files
@ -96,12 +95,6 @@ rpc: db files
netgroup: nis</programlisting>
<para>Note that <command>nss-resolve</command> will chain-load
<command>nss-dns</command> if
<filename>systemd-resolved.service</filename> is not running,
ensuring that basic DNS resolution continues to work if the
service is down.</para>
</refsect1>
<refsect1>