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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/4.5/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 are not 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>In addition to the two types of user record files and the two types of group record files there's a
fifth type of file that may be placed in the searched directories: files that indicate membership of
users in groups. Specifically, for every pair of user/group where the user shall be a member of a group a
file named
<literal><replaceable>username</replaceable>:<replaceable>groupname</replaceable>.membership</literal>
must be created, i.e. the textual UNIX user name, followed by a colon, followed by the textual UNIX group
name, suffixed by <literal>.membership</literal>. The contents of these files are currently not read,
however it is recommended to create them containing an empty JSON object
(i.e. <literal>{}</literal>). The mere existence of these files is enough to affect a user/group
membership. If a program provides user and/or group record files in the searched directories, it must
always also create such files, both for primary and auxiliary group memberships.</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>
<para>The <filename>systemd-userdb-load-credentials.service</filename> service automatically runs at boot
and installs these files from user records passed in via system credentials. See
<citerefentry><refentrytitle>userdbctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
<citerefentry><refentrytitle>systemd.system-credentials</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details.</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><simplelist type="inline">
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd-userdbd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>userdbctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd.system-credentials</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
<member><citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
<member><citerefentry project='man-pages'><refentrytitle>getent</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
</simplelist></para>
</refsect1>
</refentry>
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