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d1b04f47e3
This has been a glaring omission the docs: when people create .user/.group/.user-privileged/.group-privileged drop-in files, they should also create matching .membership files.
195 lines
11 KiB
XML
195 lines
11 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="nss-systemd" conditional='ENABLE_NSS_SYSTEMD'>
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<refentryinfo>
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<title>nss-systemd</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>nss-systemd</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>nss-systemd</refname>
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<refname>libnss_systemd.so.2</refname>
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<refpurpose>UNIX user and group name resolution for user/group lookup via Varlink</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>libnss_systemd.so.2</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>nss-systemd</command> is a plug-in module for the GNU Name Service Switch (NSS)
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functionality of the GNU C Library (<command>glibc</command>), providing UNIX user and group name
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resolution for services implementing the <ulink url="https://systemd.io/USER_GROUP_API">User/Group Record
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Lookup API via Varlink</ulink>, such as the system and service manager
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> (for its
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<varname>DynamicUser=</varname> feature, see
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
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details),
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<citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, or <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
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<para>This module also ensures that the root and nobody users and groups (i.e. the users/groups with the UIDs/GIDs
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0 and 65534) remain resolvable at all times, even if they aren't listed in <filename>/etc/passwd</filename> or
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<filename>/etc/group</filename>, or if these files are missing.</para>
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<para>This module preferably utilizes
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<citerefentry><refentrytitle>systemd-userdbd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for resolving users and groups, but also works without the service running.</para>
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<para>To activate the NSS module, add <literal>systemd</literal> to the lines starting with
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<literal>passwd:</literal>, <literal>group:</literal>, <literal>shadow:</literal> and
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<literal>gshadow:</literal> in <filename>/etc/nsswitch.conf</filename>.</para>
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<para>It is recommended to place <literal>systemd</literal> after the <literal>files</literal> entry of
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the <filename>/etc/nsswitch.conf</filename> lines so that <filename>/etc/passwd</filename>,
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<filename>/etc/group</filename>, <filename>/etc/shadow</filename> and <filename>/etc/gshadow</filename>
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based mappings take precedence.</para>
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</refsect1>
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<refsect1>
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<title>Static Drop-In JSON User/Group Records</title>
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<para>Besides user/group records acquired via the aforementioned Varlink IPC interfaces and the
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synthesized root and nobody accounts, this module also makes user and group accounts available to the
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system that are defined in static drop-in files in the <filename>/etc/userdb/</filename>,
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<filename>/run/userdb/</filename>, <filename>/run/host/userdb/</filename> and
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<filename>/usr/lib/userdb/</filename> directories.</para>
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<para>This is a simple mechanism to provide static user and group records via JSON drop-in files. Such
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user records should be defined in the format described by the <ulink
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url="https://systemd.io/USER_RECORD">JSON User Records</ulink> specification and be placed in one of the
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aforementioned directories under a file name composed of the user name suffixed with
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<filename>.user</filename>, with a world-readable access mode. A symlink named after the user record's
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UID formatted in decimal and suffixed with <filename>.user</filename> pointing to the primary record file
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should be created as well, in order to allow both lookups by username and by UID. Privileged user record
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data (e.g. hashed UNIX passwords) may optionally be provided as well, in a pair of separate companion
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files with the <filename>.user-privileged</filename> suffix. The data should be stored in a regular file
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named after the user name, suffixed with <filename>.user-privileged</filename>, and a symlink pointing to
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it, named after the used numeric UID formatted in decimal with the same suffix. These companion files
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should not be readable to anyone but root. Example:</para>
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<programlisting>-rw-r--r--. 1 root root 723 May 10 foobar.user
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-rw-------. 1 root root 123 May 10 foobar.user-privileged
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lrwxrwxrwx. 1 root root 19 May 10 4711.user -> foobar.user
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lrwxrwxrwx. 1 root root 19 May 10 4711.user-privileged -> foobar.user-privileged</programlisting>
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<para>Similarly, group records following the format described in <ulink
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url="https://systemd.io/GROUP_RECORD">JSON Group Record</ulink> may be defined, using the file suffixes
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<filename>.group</filename> and <filename>.group-privileged</filename>.</para>
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<para>The primary user/group record files (i.e. those with the <filename>.user</filename> and
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<filename>.group</filename> suffixes) should not contain the <literal>privileged</literal> section as
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described in the specifications. The privileged user/group record files (i.e. those with the
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<filename>.user-privileged</filename> and <filename>.group-privileged</filename> suffixes) should
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contain this section, exclusively.</para>
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<para>In addition to the two types of user record files and the two types of group record files there's a
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fifth type of file that may be placed in the searched directories: files that indicate membership of
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users in groups. Specifically, for every pair of user/group where the user shall be a member of a group a
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file named
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<literal><replaceable>username</replaceable>:<replaceable>groupname</replaceable>.membership</literal>
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should be created, i.e. the textual UNIX user name, followed by a colon, followed by the textual UNIX
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group name, suffixed by <literal>.membership</literal>. The contents of these files are currently not
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read, and the files should be created empty. The mere existence of these files is enough to effect a
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user/group membership. If a program provides user and/or group record files in the searched directories,
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it should always also create such files, both for primary and auxiliary group memberships.</para>
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<para>Note that static user/group records generally do not override conflicting records in
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<filename>/etc/passwd</filename> or <filename>/etc/group</filename> or other account databases. In fact,
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before dropping in these files a reasonable level of care should be taken to avoid user/group name and
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UID/GID conflicts.</para>
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</refsect1>
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<refsect1>
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<title>Configuration in <filename>/etc/nsswitch.conf</filename></title>
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<para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
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<command>nss-systemd</command> correctly:</para>
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<!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
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<programlisting>passwd: files <command>systemd</command>
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group: files <command>[SUCCESS=merge] systemd</command>
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shadow: files <command>systemd</command>
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gshadow: files <command>systemd</command>
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hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns
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networks: files
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protocols: db files
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services: db files
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ethers: db files
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rpc: db files
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netgroup: nis</programlisting>
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</refsect1>
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<refsect1>
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<title>Example: Mappings provided by <filename>systemd-machined.service</filename></title>
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<para>The container <literal>rawhide</literal> is spawned using
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<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>:
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</para>
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<programlisting># systemd-nspawn -M rawhide --boot --network-veth --private-users=pick
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Spawning container rawhide on /var/lib/machines/rawhide.
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Selected user namespace base 20119552 and range 65536.
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...
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$ machinectl --max-addresses=3
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MACHINE CLASS SERVICE OS VERSION ADDRESSES
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rawhide container systemd-nspawn fedora 30 169.254.40.164 fe80::94aa:3aff:fe7b:d4b9
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$ getent passwd vu-rawhide-0 vu-rawhide-81
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vu-rawhide-0:*:20119552:65534:vu-rawhide-0:/:/usr/sbin/nologin
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vu-rawhide-81:*:20119633:65534:vu-rawhide-81:/:/usr/sbin/nologin
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$ getent group vg-rawhide-0 vg-rawhide-81
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vg-rawhide-0:*:20119552:
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vg-rawhide-81:*:20119633:
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$ ps -o user:15,pid,tty,command -e|grep '^vu-rawhide'
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vu-rawhide-0 692 ? /usr/lib/systemd/systemd
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vu-rawhide-0 731 ? /usr/lib/systemd/systemd-journald
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vu-rawhide-192 734 ? /usr/lib/systemd/systemd-networkd
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vu-rawhide-193 738 ? /usr/lib/systemd/systemd-resolved
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vu-rawhide-0 742 ? /usr/lib/systemd/systemd-logind
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vu-rawhide-81 744 ? /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
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vu-rawhide-0 746 ? /usr/sbin/sshd -D ...
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vu-rawhide-0 752 ? /usr/lib/systemd/systemd --user
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vu-rawhide-0 753 ? (sd-pam)
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vu-rawhide-0 1628 ? login -- zbyszek
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vu-rawhide-1000 1630 ? /usr/lib/systemd/systemd --user
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vu-rawhide-1000 1631 ? (sd-pam)
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vu-rawhide-1000 1637 pts/8 -zsh
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</programlisting>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-userdbd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
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<member><citerefentry project='man-pages'><refentrytitle>getent</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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