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<?xml version='1.0'?> <!--*-nxml-*-->
<!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="systemd-userdbd.service" conditional='ENABLE_USERDB'>
<refentryinfo>
<title>systemd-userdbd.service</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-userdbd.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-userdbd.service</refname>
<refname>systemd-userdbd</refname>
<refpurpose>JSON User/Group Record Query Multiplexer/NSS Compatibility</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-userdbd.service</filename></para>
<para><filename>/usr/lib/systemd/systemd-userdbd</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>systemd-userdbd</command> is a system service that multiplexes user/group lookups to all
local services that provide JSON user/group record definitions to the system. In addition it synthesizes
JSON user/group records from classic UNIX/glibc NSS user/group records in order to provide full backwards
compatibility. It may also pick up statically defined JSON user/group records from files in
<filename>/etc/userdb/</filename>, <filename>/run/userdb/</filename>,
<filename>/run/host/userdb/</filename> and <filename>/usr/lib/userdb/</filename> with the
<literal>.user</literal> extension.</para>
<para>Most of <command>systemd-userdbd</command>'s functionality is accessible through the
<citerefentry><refentrytitle>userdbctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
command.</para>
<para>The user and group records this service provides access to follow the <ulink
url="https://systemd.io/USER_RECORD">JSON User Records</ulink> and <ulink
url="https://systemd.io/GROUP_RECORD">JSON Group Record</ulink> definitions. This service implements the
<ulink url="https://systemd.io/USER_GROUP_API">User/Group Record Lookup API via Varlink</ulink>, and
multiplexes access other services implementing this API, too. It is thus both server and client of this
API.</para>
<para>This service provides three distinct <ulink url="https://varlink.org/">Varlink</ulink> services:
<constant>io.systemd.Multiplexer</constant> provides a single, unified API for querying JSON user and
group records. Internally it talks to all other user/group record services running on the system in
parallel and forwards any information discovered. This simplifies clients substantially since they need
to talk to a single service only instead of all of them in
parallel. <constant>io.systemd.NameServiceSwitch</constant> provides compatibility with classic
UNIX/glibc NSS user records, i.e. converts <type>struct passwd</type> and <type>struct group</type>
records as acquired with APIs such as <citerefentry
project='man-pages'><refentrytitle>getpwnam</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
JSON user/group records, thus hiding the differences between the services as much as
possible. <constant>io.systemd.DropIn</constant> makes JSON user/group records from the aforementioned
drop-in directories available.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>userdbctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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