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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="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>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),
+ <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, or <citerefentry><refentrytitle>systemd-machined.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>, <literal>group:</literal>, <literal>shadow:</literal> and
+ <literal>gshadow:</literal> in <filename>/etc/nsswitch.conf</filename>.</para>
+
+ <para>It is recommended to place <literal>systemd</literal> after the <literal>files</literal> entry of
+ the <filename>/etc/nsswitch.conf</filename> lines so that <filename>/etc/passwd</filename>,
+ <filename>/etc/group</filename>, <filename>/etc/shadow</filename> and <filename>/etc/gshadow</filename>
+ based mappings take precedence.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Static Drop-In JSON User/Group Records</title>
+
+ <para>Besides user/group records acquired via the aforementioned Varlink IPC interfaces and the
+ synthesized root and nobody accounts, this module also makes user and group accounts available to the
+ system that are defined in static drop-in files in the <filename>/etc/userdb/</filename>,
+ <filename>/run/userdb/</filename>, <filename>/run/host/userdb/</filename> and
+ <filename>/usr/lib/userdb/</filename> directories.</para>
+
+ <para>This is a simple mechanism to provide static user and group records via JSON drop-in files. Such
+ user records should be defined in the format described by the <ulink
+ url="https://systemd.io/USER_RECORD">JSON User Records</ulink> specification and be placed in one of the
+ aforementioned directories under a file name composed of the user name suffixed with
+ <filename>.user</filename>, with a world-readable access mode. A symlink named after the user record's
+ UID formatted in decimal and suffixed with <filename>.user</filename> pointing to the primary record file
+ should be created as well, in order to allow both lookups by username and by UID. Privileged user record
+ data (e.g. hashed UNIX passwords) may optionally be provided as well, in a pair of separate companion
+ files with the <filename>.user-privileged</filename> suffix. The data should be stored in a regular file
+ named after the user name, suffixed with <filename>.user-privileged</filename>, and a symlink pointing to
+ it, named after the used numeric UID formatted in decimal with the same suffix. These companion files
+ should not be readable to anyone but root. Example:</para>
+
+ <programlisting>-rw-r--r--. 1 root root 723 May 10 foobar.user
+-rw-------. 1 root root 123 May 10 foobar.user-privileged
+lrwxrwxrwx. 1 root root 19 May 10 4711.user -> foobar.user
+lrwxrwxrwx. 1 root root 19 May 10 4711.user-privileged -> foobar.user-privileged</programlisting>
+
+ <para>Similarly, group records following the format described in <ulink
+ url="https://systemd.io/GROUP_RECORD">JSON Group Record</ulink> may be defined, using the file suffixes
+ <filename>.group</filename> and <filename>.group-privileged</filename>.</para>
+
+ <para>The primary user/group record files (i.e. those with the <filename>.user</filename> and
+ <filename>.group</filename> suffixes) should not contain the <literal>privileged</literal> section as
+ described in the specifications. The privileged user/group record files (i.e. those with the
+ <filename>.user-privileged</filename> and <filename>.group-privileged</filename> suffixes) should
+ contain this section, exclusively.</para>
+
+ <para>Note that static user/group records generally do not override conflicting records in
+ <filename>/etc/passwd</filename> or <filename>/etc/group</filename> or other account databases. In fact,
+ before dropping in these files a reasonable level of care should be taken to avoid user/group name and
+ UID/GID conflicts.</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-systemd</command> correctly:</para>
+
+ <!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
+ <programlisting>passwd: files <command>systemd</command>
+group: files <command>[SUCCESS=merge] systemd</command>
+shadow: files <command>systemd</command>
+gshadow: files <command>systemd</command>
+
+hosts: mymachines 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>systemd-machined.service</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:/:/usr/sbin/nologin
+vu-rawhide-81:*:20119633:65534:vu-rawhide-81:/:/usr/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
+</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><refentrytitle>systemd-userdbd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-machined.service</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>