systemd-stable/man/nss-systemd.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">
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<refentry id="nss-systemd" conditional='ENABLE_NSS_SYSTEMD'>

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

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

  <refnamediv>
    <refname>nss-systemd</refname>
    <refname>libnss_systemd.so.2</refname>
    <refpurpose>Provide UNIX user and group name resolution for user/group lookup via Varlink</refpurpose>
  </refnamediv>

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

  <refsect1>
    <title>Description</title>

    <para><command>nss-systemd</command> is a plug-in module for the GNU Name Service Switch (NSS)
    functionality of the GNU C Library (<command>glibc</command>), providing UNIX user and group name
    resolution for services implementing the <ulink url="https://systemd.io/USER_GROUP_API">User/Group Record
    Lookup API via Varlink</ulink>, such as the system and service manager
    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> (for its
    <varname>DynamicUser=</varname> feature, see
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
    details) or
    <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>

    <para>This module also ensures that the root and nobody users and groups (i.e. the users/groups with the UIDs/GIDs
    0 and 65534) remain resolvable at all times, even if they aren't listed in <filename>/etc/passwd</filename> or
    <filename>/etc/group</filename>, or if these files are missing.</para>

    <para>This module preferably utilizes
    <citerefentry><refentrytitle>systemd-userdbd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    for resolving users and groups, but also works without the service running.</para>

    <para>To activate the NSS module, add <literal>systemd</literal> to the lines starting with
    <literal>passwd:</literal> and <literal>group:</literal> in <filename>/etc/nsswitch.conf</filename>.</para>

    <para>It is recommended to place <literal>systemd</literal> after the <literal>files</literal> or
    <literal>compat</literal> entry of the <filename>/etc/nsswitch.conf</filename> lines so that
    <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>nss-systemd</command> correctly:</para>

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

hosts:          mymachines resolve [!UNAVAIL=return] myhostname files dns
networks:       files

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

netgroup:       nis</programlisting>

  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>nss-mymachines</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>