man/nss-systemd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="nss-systemd" conditional='ENABLE_NSS_SYSTEMD'>
   7
   8   <refentryinfo>
   9     <title>nss-systemd</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>nss-systemd</refentrytitle>
  15     <manvolnum>8</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>nss-systemd</refname>
  20     <refname>libnss_systemd.so.2</refname>
  21     <refpurpose>UNIX user and group name resolution for user/group lookup via Varlink</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <para><filename>libnss_systemd.so.2</filename></para>
  26   </refsynopsisdiv>
  27
  28   <refsect1>
  29     <title>Description</title>
  30
  31     <para><command>nss-systemd</command> is a plug-in module for the GNU Name Service Switch (NSS)
  32     functionality of the GNU C Library (<command>glibc</command>), providing UNIX user and group name
  33     resolution for services implementing the <ulink url="https://systemd.io/USER_GROUP_API">User/Group Record
  34     Lookup API via Varlink</ulink>, such as the system and service manager
  35     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> (for its
  36     <varname>DynamicUser=</varname> feature, see
  37     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
  38     details),
  39     <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, or <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
  40
  41     <para>This module also ensures that the root and nobody users and groups (i.e. the users/groups with the UIDs/GIDs
  42     0 and 65534) remain resolvable at all times, even if they aren't listed in <filename>/etc/passwd</filename> or
  43     <filename>/etc/group</filename>, or if these files are missing.</para>
  44
  45     <para>This module preferably utilizes
  46     <citerefentry><refentrytitle>systemd-userdbd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  47     for resolving users and groups, but also works without the service running.</para>
  48
  49     <para>To activate the NSS module, add <literal>systemd</literal> to the lines starting with
  50     <literal>passwd:</literal> and <literal>group:</literal> in <filename>/etc/nsswitch.conf</filename>.</para>
  51
  52     <para>It is recommended to place <literal>systemd</literal> after the <literal>files</literal> or
  53     <literal>compat</literal> entry of the <filename>/etc/nsswitch.conf</filename> lines so that
  54     <filename>/etc/passwd</filename> and <filename>/etc/group</filename> based mappings take precedence.</para>
  55   </refsect1>
  56
  57   <refsect1>
  58     <title>Configuration in <filename>/etc/nsswitch.conf</filename></title>
  59
  60     <para>Here is an example <filename>/etc/nsswitch.conf</filename> file that enables
  61     <command>nss-systemd</command> correctly:</para>
  62
  63     <!-- synchronize with other nss-* man pages and factory/etc/nsswitch.conf -->
  64     <programlisting>passwd:         compat <command>systemd</command>
  65 group:          compat [SUCCESS=merge] <command>systemd</command>
  66 shadow:         compat
  67
  68 hosts:          mymachines resolve [!UNAVAIL=return] myhostname files dns
  69 networks:       files
  70
  71 protocols:      db files
  72 services:       db files
  73 ethers:         db files
  74 rpc:            db files
  75
  76 netgroup:       nis</programlisting>
  77
  78   </refsect1>
  79
  80   <refsect1>
  81     <title>Example: Mappings provided by <filename>systemd-machined.service</filename></title>
  82
  83     <para>The container <literal>rawhide</literal> is spawned using
  84     <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>:
  85     </para>
  86
  87     <programlisting># systemd-nspawn -M rawhide --boot --network-veth --private-users=pick
  88 Spawning container rawhide on /var/lib/machines/rawhide.
  89 Selected user namespace base 20119552 and range 65536.
  90 ...
  91
  92 $ machinectl --max-addresses=3
  93 MACHINE CLASS     SERVICE        OS     VERSION ADDRESSES
  94 rawhide container systemd-nspawn fedora 30      169.254.40.164 fe80::94aa:3aff:fe7b:d4b9
  95
  96 $ getent passwd vu-rawhide-0 vu-rawhide-81
  97 vu-rawhide-0:*:20119552:65534:vu-rawhide-0:/:/usr/sbin/nologin
  98 vu-rawhide-81:*:20119633:65534:vu-rawhide-81:/:/usr/sbin/nologin
  99
 100 $ getent group vg-rawhide-0 vg-rawhide-81
 101 vg-rawhide-0:*:20119552:
 102 vg-rawhide-81:*:20119633:
 103
 104 $ ps -o user:15,pid,tty,command -e|grep '^vu-rawhide'
 105 vu-rawhide-0      692 ?        /usr/lib/systemd/systemd
 106 vu-rawhide-0      731 ?        /usr/lib/systemd/systemd-journald
 107 vu-rawhide-192    734 ?        /usr/lib/systemd/systemd-networkd
 108 vu-rawhide-193    738 ?        /usr/lib/systemd/systemd-resolved
 109 vu-rawhide-0      742 ?        /usr/lib/systemd/systemd-logind
 110 vu-rawhide-81     744 ?        /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
 111 vu-rawhide-0      746 ?        /usr/sbin/sshd -D ...
 112 vu-rawhide-0      752 ?        /usr/lib/systemd/systemd --user
 113 vu-rawhide-0      753 ?        (sd-pam)
 114 vu-rawhide-0     1628 ?        login -- zbyszek
 115 vu-rawhide-1000  1630 ?        /usr/lib/systemd/systemd --user
 116 vu-rawhide-1000  1631 ?        (sd-pam)
 117 vu-rawhide-1000  1637 pts/8    -zsh
 118 </programlisting>
 119   </refsect1>
 120
 121   <refsect1>
 122     <title>See Also</title>
 123     <para>
 124       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 125       <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 126       <citerefentry><refentrytitle>nss-resolve</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 127       <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 128       <citerefentry><refentrytitle>nss-mymachines</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 129       <citerefentry><refentrytitle>systemd-userdbd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 130       <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 131       <citerefentry><refentrytitle>systemd-machined.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 132       <citerefentry project='man-pages'><refentrytitle>nsswitch.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 133       <citerefentry project='man-pages'><refentrytitle>getent</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 134     </para>
 135   </refsect1>
 136
 137 </refentry>