mirror of
https://github.com/morgan9e/systemd
synced 2026-04-14 00:14:32 +09:00
b97fccf0ce
First, let's say "must" rather than "shall" regarding creation of these
files, because without them group memberships will not work.
Secondly, suggest placing an empty JSON object in them, rather than
making them empty, simply to avoid issues with older systems that didn't
backport d6570eafe3.
Fixes: #38943
204 lines
12 KiB
XML
204 lines
12 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 are not 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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must be created, i.e. the textual UNIX user name, followed by a colon, followed by the textual UNIX group
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name, suffixed by <literal>.membership</literal>. The contents of these files are currently not read,
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however it is recommended to create them containing an empty JSON object
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(i.e. <literal>{}</literal>). The mere existence of these files is enough to affect a user/group
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membership. If a program provides user and/or group record files in the searched directories, it must
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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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<para>The <filename>systemd-userdb-load-credentials.service</filename> service automatically runs at boot
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and installs these files from user records passed in via system credentials. See
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<citerefentry><refentrytitle>userdbctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
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<citerefentry><refentrytitle>systemd.system-credentials</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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for details.</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><refentrytitle>userdbctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd.system-credentials</refentrytitle><manvolnum>7</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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