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