1<?xml version="1.0"?>
2<!--*-nxml-*-->
3<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
4  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
5<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
6<refentry id="sysusers.d" conditional='ENABLE_SYSUSERS'
7    xmlns:xi="http://www.w3.org/2001/XInclude">
8
9  <refentryinfo>
10    <title>sysusers.d</title>
11    <productname>systemd</productname>
12  </refentryinfo>
13
14  <refmeta>
15    <refentrytitle>sysusers.d</refentrytitle>
16    <manvolnum>5</manvolnum>
17  </refmeta>
18
19  <refnamediv>
20    <refname>sysusers.d</refname>
21    <refpurpose>Declarative allocation of system users and groups</refpurpose>
22  </refnamediv>
23
24  <refsynopsisdiv>
25    <para><filename>/etc/sysusers.d/*.conf</filename></para>
26    <para><filename>/run/sysusers.d/*.conf</filename></para>
27    <para><filename>/usr/lib/sysusers.d/*.conf</filename></para>
28
29    <programlisting>
30#Type Name       ID                  GECOS              Home directory Shell
31u     user_name  uid                 "User Description" /home/dir      /path/to/shell
32u     user_name  uid:gid             "User Description" /home/dir      /path/to/shell
33u     user_name  /file/owned/by/user "User Description" /home/dir      /path/to/shell
34g     group_name gid
35g     group_name /file/owned/by/group
36m     user_name  group_name
37r     -          lowest-highest</programlisting>
38  </refsynopsisdiv>
39
40  <refsect1>
41    <title>Description</title>
42
43    <para><command>systemd-sysusers</command> uses the files from
44    <filename>sysusers.d</filename> directory to create system users and groups and
45    to add users to groups, at package installation or boot time. This tool may be
46    used to allocate system users and groups only, it is not useful for creating
47    non-system (i.e. regular, "human") users and groups, as it accesses
48    <filename>/etc/passwd</filename> and <filename>/etc/group</filename> directly,
49    bypassing any more complex user databases, for example any database involving NIS
50    or LDAP.</para>
51  </refsect1>
52
53  <refsect1>
54    <title>Configuration Directories and Precedence</title>
55
56    <para>Each configuration file shall be named in the style of
57    <filename><replaceable>package</replaceable>.conf</filename> or
58    <filename><replaceable>package</replaceable>-<replaceable>part</replaceable>.conf</filename>.
59    The second variant should be used when it is desirable to make it
60    easy to override just this part of configuration.</para>
61
62    <para>Files in <filename>/etc/sysusers.d</filename> override files
63    with the same name in <filename>/usr/lib/sysusers.d</filename> and
64    <filename>/run/sysusers.d</filename>. Files in
65    <filename>/run/sysusers.d</filename> override files with the same
66    name in <filename>/usr/lib/sysusers.d</filename>. Packages should
67    install their configuration files in
68    <filename>/usr/lib/sysusers.d</filename>. Files in
69    <filename>/etc/sysusers.d</filename> are reserved for the local
70    administrator, who may use this logic to override the
71    configuration files installed by vendor packages. All
72    configuration files are sorted by their filename in lexicographic
73    order, regardless of which of the directories they reside in. If
74    multiple files specify the same path, the entry in the file with
75    the lexicographically earliest name will be applied. All later
76    entries for the same user and group names will be logged as warnings.
77    </para>
78
79    <para>If the administrator wants to disable a configuration file
80    supplied by the vendor, the recommended way is to place a symlink
81    to <filename>/dev/null</filename> in
82    <filename>/etc/sysusers.d/</filename> bearing the same filename.
83    </para>
84  </refsect1>
85
86  <refsect1>
87    <title>Configuration File Format</title>
88
89    <para>The file format is one line per user or group containing name, ID, GECOS
90    field description, home directory, and login shell:</para>
91
92    <programlisting>#Type Name     ID             GECOS                 Home directory Shell
93u     httpd    404            "HTTP User"
94u     _authd   /usr/bin/authd "Authorization user"
95u     postgres -              "Postgresql Database" /var/lib/pgsql /usr/libexec/postgresdb
96g     input    -              -
97m     _authd   input
98u     root     0              "Superuser"           /root          /bin/zsh
99r     -        500-900
100</programlisting>
101
102    <para>Empty lines and lines beginning with the <literal>#</literal> character are ignored, and may be used for
103    commenting.</para>
104
105    <refsect2>
106      <title>Type</title>
107
108      <para>The type consists of a single letter. The following line
109      types are understood:</para>
110
111      <variablelist>
112        <varlistentry>
113          <term><varname>u</varname></term>
114          <listitem><para>Create a system user and group of the specified name should
115          they not exist yet. The user's primary group will be set to the group
116          bearing the same name unless the ID field specifies it. The account will be
117          created disabled, so that logins are not allowed.</para></listitem>
118        </varlistentry>
119
120        <varlistentry>
121          <term><varname>g</varname></term>
122          <listitem><para>Create a system group of the specified name
123          should it not exist yet. Note that <varname>u</varname>
124          implicitly creates a matching group. The group will be
125          created with no password set.</para></listitem>
126        </varlistentry>
127
128        <varlistentry>
129          <term><varname>m</varname></term>
130          <listitem><para>Add a user to a group. If the user or group
131          do not exist yet, they will be implicitly
132          created.</para></listitem>
133        </varlistentry>
134
135        <varlistentry>
136          <term><varname>r</varname></term>
137          <listitem><para>Add a range of numeric UIDs/GIDs to the pool
138          to allocate new UIDs and GIDs from. If no line of this type
139          is specified, the range of UIDs/GIDs is set to some
140          compiled-in default. Note that both UIDs and GIDs are
141          allocated from the same pool, in order to ensure that users
142          and groups of the same name are likely to carry the same
143          numeric UID and GID.</para></listitem>
144        </varlistentry>
145
146      </variablelist>
147    </refsect2>
148
149    <refsect2>
150      <title>Name</title>
151
152      <para>The name field specifies the user or group name. The specified name must consist only of the characters a-z,
153      A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character which must be one of a-z,
154      A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted as first character). The
155      user/group name must have at least one character, and at most 31.</para>
156
157      <para>For further details about the syntax of user/group names, see <ulink
158      url="https://systemd.io/USER_NAMES">User/Group Name Syntax</ulink>.</para>
159
160      <para>It is strongly recommended to pick user and group names that are unlikely to clash with normal users
161      created by the administrator. A good scheme to guarantee this is by prefixing all system and group names with the
162      underscore, and avoiding too generic names.</para>
163
164      <para>For <varname>m</varname> lines, this field should contain
165      the user name to add to a group.</para>
166
167      <para>For lines of type <varname>r</varname>, this field should
168      be set to <literal>-</literal>.</para>
169    </refsect2>
170
171    <refsect2>
172      <title>ID</title>
173
174      <para>For <varname>u</varname> and <varname>g</varname>, the
175      numeric 32-bit UID or GID of the user/group. Do not use IDs 65535
176      or 4294967295, as they have special placeholder meanings.
177      Specify <literal>-</literal> for automatic UID/GID allocation
178      for the user or group (this is strongly recommended unless it is strictly
179      necessary to use a specific UID or GID). Alternatively, specify an absolute path
180      in the file system. In this case, the UID/GID is read from the
181      path's owner/group. This is useful to create users whose UID/GID
182      match the owners of pre-existing files (such as SUID or SGID
183      binaries).
184      The syntaxes <literal><replaceable>uid</replaceable>:<replaceable>gid</replaceable></literal> and
185      <literal><replaceable>uid</replaceable>:<replaceable>groupname</replaceable></literal> are supported to
186      allow creating users with specific primary groups. The given group must be created explicitly, or it
187      must already exist. Specifying <literal>-</literal> for the UID in these syntaxes is also supported.
188      </para>
189
190      <para>For <varname>m</varname> lines, this field should contain
191      the group name to add to a user to.</para>
192
193      <para>For lines of type <varname>r</varname>, this field should
194      be set to a UID/GID range in the format
195      <literal>FROM-TO</literal>, where both values are formatted as
196      decimal ASCII numbers. Alternatively, a single UID/GID may be
197      specified formatted as decimal ASCII numbers.</para>
198    </refsect2>
199
200    <refsect2>
201      <title>GECOS</title>
202
203      <para>A short, descriptive string for users to be created, enclosed in
204      quotation marks. Note that this field may not contain colons.</para>
205
206      <para>Only applies to lines of type <varname>u</varname> and should otherwise
207      be left unset (or <literal>-</literal>).</para>
208    </refsect2>
209
210    <refsect2>
211      <title>Home Directory</title>
212
213      <para>The home directory for a new system user. If omitted, defaults to the
214      root directory.</para>
215
216      <para>Only applies to lines of type <varname>u</varname> and should otherwise
217      be left unset (or <literal>-</literal>). It is recommended to omit this, unless
218      software strictly requires a home directory to be set.</para>
219
220      <para><command>systemd-sysusers</command> only sets the home directory record in the
221      user database. To actually create the directory, consider adding a corresponding
222      <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
223      fragment.</para>
224    </refsect2>
225
226    <refsect2>
227      <title>Shell</title>
228
229      <para>The login shell of the user. If not specified, this will be set to
230      <filename>/usr/sbin/nologin</filename>, except if the UID of the user is 0, in
231      which case <filename>/bin/sh</filename> will be used.</para>
232
233      <para>Only applies to lines of type <varname>u</varname> and should otherwise
234      be left unset (or <literal>-</literal>). It is recommended to omit this, unless
235      a shell different <filename>/usr/sbin/nologin</filename> must be used.</para>
236    </refsect2>
237  </refsect1>
238
239  <refsect1>
240    <title>Specifiers</title>
241
242    <para>Specifiers can be used in the <literal>Name</literal>, <literal>ID</literal>,
243    <literal>GECOS</literal>, <literal>Home directory</literal>, and <literal>Shell</literal> fields. An
244    unknown or unresolvable specifier is treated as invalid configuration. The following expansions are
245    understood:</para>
246
247    <table class='specifiers'>
248      <title>Specifiers available</title>
249      <tgroup cols='3' align='left' colsep='1' rowsep='1'>
250        <colspec colname="spec" />
251        <colspec colname="mean" />
252        <colspec colname="detail" />
253        <thead>
254          <row>
255            <entry>Specifier</entry>
256            <entry>Meaning</entry>
257            <entry>Details</entry>
258          </row>
259        </thead>
260        <tbody>
261          <xi:include href="standard-specifiers.xml" xpointer="a"/>
262          <xi:include href="standard-specifiers.xml" xpointer="A"/>
263          <xi:include href="standard-specifiers.xml" xpointer="b"/>
264          <xi:include href="standard-specifiers.xml" xpointer="B"/>
265          <xi:include href="standard-specifiers.xml" xpointer="H"/>
266          <xi:include href="standard-specifiers.xml" xpointer="l"/>
267          <xi:include href="standard-specifiers.xml" xpointer="m"/>
268          <xi:include href="standard-specifiers.xml" xpointer="M"/>
269          <xi:include href="standard-specifiers.xml" xpointer="o"/>
270          <xi:include href="standard-specifiers.xml" xpointer="T"/>
271          <xi:include href="standard-specifiers.xml" xpointer="v"/>
272          <xi:include href="standard-specifiers.xml" xpointer="V"/>
273          <xi:include href="standard-specifiers.xml" xpointer="w"/>
274          <xi:include href="standard-specifiers.xml" xpointer="W"/>
275          <xi:include href="standard-specifiers.xml" xpointer="percent"/>
276        </tbody>
277      </tgroup>
278    </table>
279  </refsect1>
280
281  <refsect1>
282    <title>Idempotence</title>
283
284    <para>Note that <command>systemd-sysusers</command> will do nothing if the
285    specified users or groups already exist or the users are members of specified
286    groups, so normally there is no reason to override
287    <filename>sysusers.d</filename> vendor configuration, except to block certain
288    users or groups from being created.</para>
289  </refsect1>
290
291  <refsect1>
292    <title>See Also</title>
293    <para>
294      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
295      <citerefentry><refentrytitle>systemd-sysusers</refentrytitle><manvolnum>8</manvolnum></citerefentry>
296    </para>
297  </refsect1>
298
299</refentry>
300