man/sysusers.d.xml

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   5   SPDX-License-Identifier: LGPL-2.1+
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   7 <refentry id="sysusers.d" conditional='ENABLE_SYSUSERS'
   8     xmlns:xi="http://www.w3.org/2001/XInclude">
   9
  10   <refentryinfo>
  11     <title>sysusers.d</title>
  12     <productname>systemd</productname>
  13   </refentryinfo>
  14
  15   <refmeta>
  16     <refentrytitle>sysusers.d</refentrytitle>
  17     <manvolnum>5</manvolnum>
  18   </refmeta>
  19
  20   <refnamediv>
  21     <refname>sysusers.d</refname>
  22     <refpurpose>Declarative allocation of system users and groups</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <para><filename>/etc/sysusers.d/*.conf</filename></para>
  27     <para><filename>/run/sysusers.d/*.conf</filename></para>
  28     <para><filename>/usr/lib/sysusers.d/*.conf</filename></para>
  29   </refsynopsisdiv>
  30
  31   <refsect1>
  32     <title>Description</title>
  33
  34     <para><command>systemd-sysusers</command> uses the files from
  35     <filename>sysusers.d</filename> directory to create system users and groups and
  36     to add users to groups, at package installation or boot time. This tool may be
  37     used to allocate system users and groups only, it is not useful for creating
  38     non-system (i.e. regular, "human") users and groups, as it accesses
  39     <filename>/etc/passwd</filename> and <filename>/etc/group</filename> directly,
  40     bypassing any more complex user databases, for example any database involving NIS
  41     or LDAP.</para>
  42   </refsect1>
  43
  44   <refsect1>
  45     <title>Configuration Directories and Precedence</title>
  46
  47     <para>Each configuration file shall be named in the style of
  48     <filename><replaceable>package</replaceable>.conf</filename> or
  49     <filename><replaceable>package</replaceable>-<replaceable>part</replaceable>.conf</filename>.
  50     The second variant should be used when it is desirable to make it
  51     easy to override just this part of configuration.</para>
  52
  53     <para>Files in <filename>/etc/sysusers.d</filename> override files
  54     with the same name in <filename>/usr/lib/sysusers.d</filename> and
  55     <filename>/run/sysusers.d</filename>. Files in
  56     <filename>/run/sysusers.d</filename> override files with the same
  57     name in <filename>/usr/lib/sysusers.d</filename>. Packages should
  58     install their configuration files in
  59     <filename>/usr/lib/sysusers.d</filename>. Files in
  60     <filename>/etc/sysusers.d</filename> are reserved for the local
  61     administrator, who may use this logic to override the
  62     configuration files installed by vendor packages. All
  63     configuration files are sorted by their filename in lexicographic
  64     order, regardless of which of the directories they reside in. If
  65     multiple files specify the same path, the entry in the file with
  66     the lexicographically earliest name will be applied. All later
  67     entries for the same user and group names will be logged as warnings.
  68     </para>
  69
  70     <para>If the administrator wants to disable a configuration file
  71     supplied by the vendor, the recommended way is to place a symlink
  72     to <filename>/dev/null</filename> in
  73     <filename>/etc/sysusers.d/</filename> bearing the same filename.
  74     </para>
  75   </refsect1>
  76
  77   <refsect1>
  78     <title>Configuration File Format</title>
  79
  80     <para>The file format is one line per user or group containing name, ID, GECOS
  81     field description, home directory, and login shell:</para>
  82
  83     <programlisting>#Type Name     ID             GECOS                 Home directory Shell
  84 u     httpd    404            "HTTP User"
  85 u     authd    /usr/bin/authd "Authorization user"
  86 u     postgres -              "Postgresql Database" /var/lib/pgsql /usr/libexec/postgresdb
  87 g     input    -              -
  88 m     authd    input
  89 u     root     0              "Superuser"           /root          /bin/zsh</programlisting>
  90
  91     <para>Empty lines and lines beginning with the <literal>#</literal> character are ignored, and may be used for
  92     commenting.</para>
  93
  94     <refsect2>
  95       <title>Type</title>
  96
  97       <para>The type consists of a single letter. The following line
  98       types are understood:</para>
  99
 100       <variablelist>
 101         <varlistentry>
 102           <term><varname>u</varname></term>
 103           <listitem><para>Create a system user and group of the specified name should
 104           they not exist yet. The user's primary group will be set to the group
 105           bearing the same name. The account will be created disabled, so that logins
 106           are not allowed.</para></listitem>
 107         </varlistentry>
 108
 109         <varlistentry>
 110           <term><varname>g</varname></term>
 111           <listitem><para>Create a system group of the specified name
 112           should it not exist yet. Note that <varname>u</varname>
 113           implicitly create a matching group. The group will be
 114           created with no password set.</para></listitem>
 115         </varlistentry>
 116
 117         <varlistentry>
 118           <term><varname>m</varname></term>
 119           <listitem><para>Add a user to a group. If the user or group
 120           do not exist yet, they will be implicitly
 121           created.</para></listitem>
 122         </varlistentry>
 123
 124         <varlistentry>
 125           <term><varname>r</varname></term>
 126           <listitem><para>Add a range of numeric UIDs/GIDs to the pool
 127           to allocate new UIDs and GIDs from. If no line of this type
 128           is specified, the range of UIDs/GIDs is set to some
 129           compiled-in default. Note that both UIDs and GIDs are
 130           allocated from the same pool, in order to ensure that users
 131           and groups of the same name are likely to carry the same
 132           numeric UID and GID.</para></listitem>
 133         </varlistentry>
 134
 135       </variablelist>
 136     </refsect2>
 137
 138     <refsect2>
 139       <title>Name</title>
 140
 141       <para>The name field specifies the user or group name. The specified name must consist only of the characters a-z,
 142       A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character which must be one of a-z,
 143       A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted as first character). The
 144       user/group name must have at least one character, and at most 31.</para>
 145
 146       <para>It is strongly recommended to pick user and group names that are unlikely to clash with normal users
 147       created by the administrator. A good scheme to guarantee this is by prefixing all system and group names with the
 148       underscore, and avoiding too generic names.</para>
 149
 150       <para>For <varname>m</varname> lines, this field should contain
 151       the user name to add to a group.</para>
 152
 153       <para>For lines of type <varname>r</varname>, this field should
 154       be set to <literal>-</literal>.</para>
 155     </refsect2>
 156
 157     <refsect2>
 158       <title>ID</title>
 159
 160       <para>For <varname>u</varname> and <varname>g</varname>, the
 161       numeric 32-bit UID or GID of the user/group. Do not use IDs 65535
 162       or 4294967295, as they have special placeholder meanings.
 163       Specify <literal>-</literal> for automatic UID/GID allocation
 164       for the user or group (this is strongly recommended unless it is strictly
 165       necessary to use a specific UID or GID). Alternatively, specify an absolute path
 166       in the file system. In this case, the UID/GID is read from the
 167       path's owner/group. This is useful to create users whose UID/GID
 168       match the owners of pre-existing files (such as SUID or SGID
 169       binaries).
 170       The syntax <literal><replaceable>uid</replaceable>:<replaceable>gid</replaceable></literal> is also supported to
 171       allow creating user and group pairs with different numeric UID and GID values. The group with the indicated GID must get created explicitly before or it must already exist. Specifying <literal>-</literal> for the UID in this syntax
 172       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>/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>/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>