man/sysusers.d.xml

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   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   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
  31 u     user_name  uid                 "User Description" /home/dir      /path/to/shell
  32 u     user_name  uid:gid             "User Description" /home/dir      /path/to/shell
  33 u     user_name  /file/owned/by/user "User Description" /home/dir      /path/to/shell
  34 g     group_name gid
  35 g     group_name /file/owned/by/group
  36 m     user_name  group_name
  37 r     -          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
  93 u     httpd    404            "HTTP User"
  94 u     _authd   /usr/bin/authd "Authorization user"
  95 u     postgres -              "Postgresql Database" /var/lib/pgsql /usr/libexec/postgresdb
  96 g     input    -              -
  97 m     _authd   input
  98 u     root     0              "Superuser"           /root          /bin/zsh
  99 r     -        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>
 118
 119           <xi:include href="version-info.xml" xpointer="v215"/></listitem>
 120         </varlistentry>
 121
 122         <varlistentry>
 123           <term><varname>g</varname></term>
 124           <listitem><para>Create a system group of the specified name
 125           should it not exist yet. Note that <varname>u</varname>
 126           implicitly creates a matching group. The group will be
 127           created with no password set.</para>
 128
 129           <xi:include href="version-info.xml" xpointer="v215"/></listitem>
 130         </varlistentry>
 131
 132         <varlistentry>
 133           <term><varname>m</varname></term>
 134           <listitem><para>Add a user to a group. If the user or group
 135           do not exist yet, they will be implicitly
 136           created.</para>
 137
 138           <xi:include href="version-info.xml" xpointer="v215"/></listitem>
 139         </varlistentry>
 140
 141         <varlistentry>
 142           <term><varname>r</varname></term>
 143           <listitem><para>Add a range of numeric UIDs/GIDs to the pool
 144           to allocate new UIDs and GIDs from. If no line of this type
 145           is specified, the range of UIDs/GIDs is set to some
 146           compiled-in default. Note that both UIDs and GIDs are
 147           allocated from the same pool, in order to ensure that users
 148           and groups of the same name are likely to carry the same
 149           numeric UID and GID.</para>
 150
 151           <xi:include href="version-info.xml" xpointer="v216"/></listitem>
 152         </varlistentry>
 153
 154       </variablelist>
 155     </refsect2>
 156
 157     <refsect2>
 158       <title>Name</title>
 159
 160       <para>The name field specifies the user or group name. The specified name must consist only of the characters a-z,
 161       A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character which must be one of a-z,
 162       A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted as first character). The
 163       user/group name must have at least one character, and at most 31.</para>
 164
 165       <para>For further details about the syntax of user/group names, see <ulink
 166       url="https://systemd.io/USER_NAMES">User/Group Name Syntax</ulink>.</para>
 167
 168       <para>It is strongly recommended to pick user and group names that are unlikely to clash with normal users
 169       created by the administrator. A good scheme to guarantee this is by prefixing all system and group names with the
 170       underscore, and avoiding too generic names.</para>
 171
 172       <para>For <varname>m</varname> lines, this field should contain
 173       the user name to add to a group.</para>
 174
 175       <para>For lines of type <varname>r</varname>, this field should
 176       be set to <literal>-</literal>.</para>
 177     </refsect2>
 178
 179     <refsect2>
 180       <title>ID</title>
 181
 182       <para>For <varname>u</varname> and <varname>g</varname>, the
 183       numeric 32-bit UID or GID of the user/group. Do not use IDs 65535
 184       or 4294967295, as they have special placeholder meanings.
 185       Specify <literal>-</literal> for automatic UID/GID allocation
 186       for the user or group (this is strongly recommended unless it is strictly
 187       necessary to use a specific UID or GID). Alternatively, specify an absolute path
 188       in the file system. In this case, the UID/GID is read from the
 189       path's owner/group. This is useful to create users whose UID/GID
 190       match the owners of pre-existing files (such as SUID or SGID
 191       binaries).
 192       The syntaxes <literal><replaceable>uid</replaceable>:<replaceable>gid</replaceable></literal> and
 193       <literal><replaceable>uid</replaceable>:<replaceable>groupname</replaceable></literal> are supported to
 194       allow creating users with specific primary groups. The given group must be created explicitly, or it
 195       must already exist. Specifying <literal>-</literal> for the UID in these syntaxes is also supported.
 196       </para>
 197
 198       <para>For <varname>m</varname> lines, this field should contain
 199       the group name to add to a user to.</para>
 200
 201       <para>For lines of type <varname>r</varname>, this field should
 202       be set to a UID/GID range in the format
 203       <literal>FROM-TO</literal>, where both values are formatted as
 204       decimal ASCII numbers. Alternatively, a single UID/GID may be
 205       specified formatted as decimal ASCII numbers.</para>
 206     </refsect2>
 207
 208     <refsect2>
 209       <title>GECOS</title>
 210
 211       <para>A short, descriptive string for users to be created, enclosed in
 212       quotation marks. Note that this field may not contain colons.</para>
 213
 214       <para>Only applies to lines of type <varname>u</varname> and should otherwise
 215       be left unset (or <literal>-</literal>).</para>
 216     </refsect2>
 217
 218     <refsect2>
 219       <title>Home Directory</title>
 220
 221       <para>The home directory for a new system user. If omitted, defaults to the
 222       root directory.</para>
 223
 224       <para>Only applies to lines of type <varname>u</varname> and should otherwise
 225       be left unset (or <literal>-</literal>). It is recommended to omit this, unless
 226       software strictly requires a home directory to be set.</para>
 227
 228       <para><command>systemd-sysusers</command> only sets the home directory record in the
 229       user database. To actually create the directory, consider adding a corresponding
 230       <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 231       fragment.</para>
 232     </refsect2>
 233
 234     <refsect2>
 235       <title>Shell</title>
 236
 237       <para>The login shell of the user. If not specified, this will be set to
 238       <filename>/usr/sbin/nologin</filename>, except if the UID of the user is 0, in
 239       which case <filename>/bin/sh</filename> will be used.</para>
 240
 241       <para>Only applies to lines of type <varname>u</varname> and should otherwise
 242       be left unset (or <literal>-</literal>). It is recommended to omit this, unless
 243       a shell different <filename>/usr/sbin/nologin</filename> must be used.</para>
 244     </refsect2>
 245   </refsect1>
 246
 247   <refsect1>
 248     <title>Specifiers</title>
 249
 250     <para>Specifiers can be used in the <literal>Name</literal>, <literal>ID</literal>,
 251     <literal>GECOS</literal>, <literal>Home directory</literal>, and <literal>Shell</literal> fields. An
 252     unknown or unresolvable specifier is treated as invalid configuration. The following expansions are
 253     understood:</para>
 254
 255     <table class='specifiers'>
 256       <title>Specifiers available</title>
 257       <tgroup cols='3' align='left' colsep='1' rowsep='1'>
 258         <colspec colname="spec" />
 259         <colspec colname="mean" />
 260         <colspec colname="detail" />
 261         <thead>
 262           <row>
 263             <entry>Specifier</entry>
 264             <entry>Meaning</entry>
 265             <entry>Details</entry>
 266           </row>
 267         </thead>
 268         <tbody>
 269           <xi:include href="standard-specifiers.xml" xpointer="a"/>
 270           <xi:include href="standard-specifiers.xml" xpointer="A"/>
 271           <xi:include href="standard-specifiers.xml" xpointer="b"/>
 272           <xi:include href="standard-specifiers.xml" xpointer="B"/>
 273           <xi:include href="standard-specifiers.xml" xpointer="H"/>
 274           <xi:include href="standard-specifiers.xml" xpointer="l"/>
 275           <xi:include href="standard-specifiers.xml" xpointer="m"/>
 276           <xi:include href="standard-specifiers.xml" xpointer="M"/>
 277           <xi:include href="standard-specifiers.xml" xpointer="o"/>
 278           <xi:include href="standard-specifiers.xml" xpointer="T"/>
 279           <xi:include href="standard-specifiers.xml" xpointer="v"/>
 280           <xi:include href="standard-specifiers.xml" xpointer="V"/>
 281           <xi:include href="standard-specifiers.xml" xpointer="w"/>
 282           <xi:include href="standard-specifiers.xml" xpointer="W"/>
 283           <xi:include href="standard-specifiers.xml" xpointer="percent"/>
 284         </tbody>
 285       </tgroup>
 286     </table>
 287   </refsect1>
 288
 289   <refsect1>
 290     <title>Idempotence</title>
 291
 292     <para>Note that <command>systemd-sysusers</command> will do nothing if the
 293     specified users or groups already exist or the users are members of specified
 294     groups, so normally there is no reason to override
 295     <filename>sysusers.d</filename> vendor configuration, except to block certain
 296     users or groups from being created.</para>
 297   </refsect1>
 298
 299   <refsect1>
 300     <title>See Also</title>
 301     <para>
 302       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 303       <citerefentry><refentrytitle>systemd-sysusers</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 304     </para>
 305   </refsect1>
 306
 307 </refentry>