man: add an extensive example to nss-mymachines(8)

The man page didn't really say what we are mapping and with what
patterns. Let's fix that.

diff --git a/man/nss-mymachines.xml b/man/nss-mymachines.xml
index a0a0f99684dd35fa5446da0b472b60546911e845..5742d89779cb591473371eb15dc9d8badbbb1ac1 100644 (file)
--- a/man/nss-mymachines.xml
+++ b/man/nss-mymachines.xml
@@ -35,12 +35,21 @@
     <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
     <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
+    <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
     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 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>
+    functionality only applies to containers using network namespacing (see the description of
+    <option>--private-network</option> in
+    <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>).
+    Note that the name that is resolved is the one registered with <command>systemd-machined</command>, which
+    may be different than the hostname configured inside of the container.</para>
+
+    <para>The module also provides name resolution for user and group identifiers mapped to containers. All names from
+    the range allocated to a given container <replaceable>container</replaceable> are exposed on the host as
+    <literal>vu-<replaceable>container</replaceable>-<replaceable>uid</replaceable></literal> and
+    <literal>vg-<replaceable>container</replaceable>-<replaceable>gid</replaceable></literal> (see example below). This
+    functionality only applies to containers using user namespacing (see the description of
+    <option>--private-users</option> in
+    <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>).</para>

 
     <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
 
     <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


@@ -53,7 +62,7 @@
   </refsect1>
 
   <refsect1>
   </refsect1>
 
   <refsect1>

-    <title>Example</title>
+    <title>Configuration in <filename>/etc/nsswitch.conf</filename></title>

 
     <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
     <command>nss-mymachines</command> correctly:</para>
 
     <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
     <command>nss-mymachines</command> correctly:</para>


@@ -75,11 +84,74 @@ netgroup:       nis</programlisting>
 
   </refsect1>
 
 
   </refsect1>
 

+  <refsect1>
+    <title>Mappings provided by <filename>nss-mymachines</filename></title>
+
+    <para>The container <literal>rawhide</literal> is spawned using
+    <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>:
+    </para>
+
+    <programlisting># systemd-nspawn -M rawhide --boot --network-veth --private-users=pick
+Spawning container rawhide on /var/lib/machines/rawhide.
+Selected user namespace base 20119552 and range 65536.
+...
+
+$ machinectl --max-addresses=3
+MACHINE CLASS     SERVICE        OS     VERSION ADDRESSES
+rawhide container systemd-nspawn fedora 30      169.254.40.164 fe80::94aa:3aff:fe7b:d4b9
+
+$ getent passwd vu-rawhide-0 vu-rawhide-81
+vu-rawhide-0:*:20119552:65534:vu-rawhide-0:/:/sbin/nologin
+vu-rawhide-81:*:20119633:65534:vu-rawhide-81:/:/sbin/nologin
+
+$ getent group vg-rawhide-0 vg-rawhide-81
+vg-rawhide-0:*:20119552:
+vg-rawhide-81:*:20119633:
+
+$ ps -o user:15,pid,tty,command -e|grep '^vu-rawhide'
+vu-rawhide-0      692 ?        /usr/lib/systemd/systemd
+vu-rawhide-0      731 ?        /usr/lib/systemd/systemd-journald
+vu-rawhide-192    734 ?        /usr/lib/systemd/systemd-networkd
+vu-rawhide-193    738 ?        /usr/lib/systemd/systemd-resolved
+vu-rawhide-0      742 ?        /usr/lib/systemd/systemd-logind
+vu-rawhide-81     744 ?        /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
+vu-rawhide-0      746 ?        /usr/sbin/sshd -D ...
+vu-rawhide-0      752 ?        /usr/lib/systemd/systemd --user
+vu-rawhide-0      753 ?        (sd-pam)
+vu-rawhide-0     1628 ?        login -- zbyszek
+vu-rawhide-1000  1630 ?        /usr/lib/systemd/systemd --user
+vu-rawhide-1000  1631 ?        (sd-pam)
+vu-rawhide-1000  1637 pts/8    -zsh
+
+$ ping -c1 rawhide
+PING rawhide(fe80::94aa:3aff:fe7b:d4b9%ve-rawhide (fe80::94aa:3aff:fe7b:d4b9%ve-rawhide)) 56 data bytes
+64 bytes from fe80::94aa:3aff:fe7b:d4b9%ve-rawhide (fe80::94aa:3aff:fe7b:d4b9%ve-rawhide): icmp_seq=1 ttl=64 time=0.045 ms
+...
+$ ping -c1 -4 rawhide
+PING rawhide (169.254.40.164) 56(84) bytes of data.
+64 bytes from 169.254.40.164 (169.254.40.164): icmp_seq=1 ttl=64 time=0.064 ms
+...
+
+# machinectl shell rawhide /sbin/ip a
+Connected to machine rawhide. Press ^] three times within 1s to exit session.
+1: lo: &lt;LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
+    ...
+2: host0@if21: &lt;BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
+    link/ether 96:aa:3a:7b:d4:b9 brd ff:ff:ff:ff:ff:ff link-netnsid 0
+    inet 169.254.40.164/16 brd 169.254.255.255 scope link host0
+       valid_lft forever preferred_lft forever
+    inet6 fe80::94aa:3aff:fe7b:d4b9/64 scope link
+       valid_lft forever preferred_lft forever
+Connection to machine rawhide terminated.
+</programlisting>
+  </refsect1>
+

   <refsect1>
     <title>See Also</title>
     <para>
       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
   <refsect1>
     <title>See Also</title>
     <para>
       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,

+      <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

       <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,