man/nss-mymachines.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="nss-mymachines" conditional='ENABLE_NSS_MYMACHINES'>

  <refentryinfo>
    <title>nss-mymachines</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>nss-mymachines</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>nss-mymachines</refname>
    <refname>libnss_mymachines.so.2</refname>
    <refpurpose>Hostname resolution for local container instances</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>libnss_mymachines.so.2</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <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 (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>Note that this NSS module only makes available names of the containers running immediately below
    the current system context. It does not provide host name resolution for containers running side-by-side
    with the invoking system context, or containers further up or down the container hierarchy. Or in other
    words, on the host system it provides host name resolution for the containers running immediately below
    the host environment. When used inside a container environment however, it will not be able to provide
    name resolution for containers running on the host (as those are siblings and not children of the current
    container environment), but instead only for nested containers running immediately below its own
    container environment.</para>

    <para>To activate the NSS module, add <literal>mymachines</literal> to the line starting with
    <literal>hosts:</literal> in <filename>/etc/nsswitch.conf</filename>.</para>

    <para>It is recommended to place <literal>mymachines</literal> before the <literal>resolve</literal> or
    <literal>dns</literal> entry of the <literal>hosts:</literal> line of
    <filename>/etc/nsswitch.conf</filename> in order to make sure that its mappings are preferred over other
    resolvers such as DNS.</para>
  </refsect1>

  <refsect1>
    <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>

    <!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
    <programlisting>passwd:         compat systemd
group:          compat [SUCCESS=merge] systemd
shadow:         compat systemd
gshadow:        files systemd

hosts:          <command>mymachines</command> resolve [!UNAVAIL=return] files myhostname dns
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis</programlisting>

  </refsect1>

  <refsect1>
    <title>Example: 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

$ 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>,
      <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 project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>getent</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>