man/sysusers.d.xml

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   7   This file is part of systemd.
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   9   Copyright 2014 Lennart Poettering
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  24 <refentry id="sysusers.d" conditional='ENABLE_SYSUSERS'
  25     xmlns:xi="http://www.w3.org/2001/XInclude">
  26
  27   <refentryinfo>
  28     <title>sysusers.d</title>
  29     <productname>systemd</productname>
  30
  31     <authorgroup>
  32       <author>
  33         <contrib>Developer</contrib>
  34         <firstname>Lennart</firstname>
  35         <surname>Poettering</surname>
  36         <email>lennart@poettering.net</email>
  37       </author>
  38     </authorgroup>
  39   </refentryinfo>
  40
  41   <refmeta>
  42     <refentrytitle>sysusers.d</refentrytitle>
  43     <manvolnum>5</manvolnum>
  44   </refmeta>
  45
  46   <refnamediv>
  47     <refname>sysusers.d</refname>
  48     <refpurpose>Declarative allocation of system users and groups</refpurpose>
  49   </refnamediv>
  50
  51   <refsynopsisdiv>
  52     <para><filename>/etc/sysusers.d/*.conf</filename></para>
  53     <para><filename>/run/sysusers.d/*.conf</filename></para>
  54     <para><filename>/usr/lib/sysusers.d/*.conf</filename></para>
  55   </refsynopsisdiv>
  56
  57   <refsect1>
  58     <title>Description</title>
  59
  60     <para><command>systemd-sysusers</command> uses the files from
  61     <filename>sysusers.d</filename> directory to create system users and groups and
  62     to add users to groups, at package installation or boot time. This tool may be
  63     used to allocate system users and groups only, it is not useful for creating
  64     non-system (i.e. regular, "human") users and groups, as it accesses
  65     <filename>/etc/passwd</filename> and <filename>/etc/group</filename> directly,
  66     bypassing any more complex user databases, for example any database involving NIS
  67     or LDAP.</para>
  68   </refsect1>
  69
  70   <refsect1>
  71     <title>Configuration Directories and Precedence</title>
  72
  73     <para>Each configuration file shall be named in the style of
  74     <filename><replaceable>package</replaceable>.conf</filename> or
  75     <filename><replaceable>package</replaceable>-<replaceable>part</replaceable>.conf</filename>.
  76     The second variant should be used when it is desirable to make it
  77     easy to override just this part of configuration.</para>
  78
  79     <para>Files in <filename>/etc/sysusers.d</filename> override files
  80     with the same name in <filename>/usr/lib/sysusers.d</filename> and
  81     <filename>/run/sysusers.d</filename>. Files in
  82     <filename>/run/sysusers.d</filename> override files with the same
  83     name in <filename>/usr/lib/sysusers.d</filename>. Packages should
  84     install their configuration files in
  85     <filename>/usr/lib/sysusers.d</filename>. Files in
  86     <filename>/etc/sysusers.d</filename> are reserved for the local
  87     administrator, who may use this logic to override the
  88     configuration files installed by vendor packages. All
  89     configuration files are sorted by their filename in lexicographic
  90     order, regardless of which of the directories they reside in. If
  91     multiple files specify the same path, the entry in the file with
  92     the lexicographically earliest name will be applied. All later
  93     entries for the same user and group names will be logged as warnings.
  94     </para>
  95
  96     <para>If the administrator wants to disable a configuration file
  97     supplied by the vendor, the recommended way is to place a symlink
  98     to <filename>/dev/null</filename> in
  99     <filename>/etc/sysusers.d/</filename> bearing the same filename.
 100     </para>
 101   </refsect1>
 102
 103   <refsect1>
 104     <title>Configuration File Format</title>
 105
 106     <para>The file format is one line per user or group containing name, ID, GECOS
 107     field description, home directory, and login shell:</para>
 108
 109     <programlisting>#Type Name     ID             GECOS                 Home directory Shell
 110 u     httpd    404            "HTTP User"
 111 u     authd    /usr/bin/authd "Authorization user"
 112 u     postgres -              "Postgresql Database" /var/lib/pgsql /usr/libexec/postgresdb
 113 g     input    -              -
 114 m     authd    input
 115 u     root     0              "Superuser"           /root          /bin/zsh</programlisting>
 116
 117     <para>Empty lines and lines beginning with the <literal>#</literal> character are ignored, and may be used for
 118     commenting.</para>
 119
 120     <refsect2>
 121       <title>Type</title>
 122
 123       <para>The type consists of a single letter. The following line
 124       types are understood:</para>
 125
 126       <variablelist>
 127         <varlistentry>
 128           <term><varname>u</varname></term>
 129           <listitem><para>Create a system user and group of the specified name should
 130           they not exist yet. The user's primary group will be set to the group
 131           bearing the same name. The account will be created disabled, so that logins
 132           are not allowed.</para></listitem>
 133         </varlistentry>
 134
 135         <varlistentry>
 136           <term><varname>g</varname></term>
 137           <listitem><para>Create a system group of the specified name
 138           should it not exist yet. Note that <varname>u</varname>
 139           implicitly create a matching group. The group will be
 140           created with no password set.</para></listitem>
 141         </varlistentry>
 142
 143         <varlistentry>
 144           <term><varname>m</varname></term>
 145           <listitem><para>Add a user to a group. If the user or group
 146           do not exist yet, they will be implicitly
 147           created.</para></listitem>
 148         </varlistentry>
 149
 150         <varlistentry>
 151           <term><varname>r</varname></term>
 152           <listitem><para>Add a range of numeric UIDs/GIDs to the pool
 153           to allocate new UIDs and GIDs from. If no line of this type
 154           is specified, the range of UIDs/GIDs is set to some
 155           compiled-in default. Note that both UIDs and GIDs are
 156           allocated from the same pool, in order to ensure that users
 157           and groups of the same name are likely to carry the same
 158           numeric UID and GID.</para></listitem>
 159         </varlistentry>
 160
 161       </variablelist>
 162     </refsect2>
 163
 164     <refsect2>
 165       <title>Name</title>
 166
 167       <para>The name field specifies the user or group name. The specified name must consist only of the characters a-z,
 168       A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character which must be one of a-z,
 169       A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted as first character). The
 170       user/group name must have at least one character, and at most 31.</para>
 171
 172       <para>It is strongly recommended to pick user and group names that are unlikely to clash with normal users
 173       created by the administrator. A good scheme to guarantee this is by prefixing all system and group names with the
 174       underscore, and avoiding too generic names.</para>
 175
 176       <para>For <varname>m</varname> lines, this field should contain
 177       the user name to add to a group.</para>
 178
 179       <para>For lines of type <varname>r</varname>, this field should
 180       be set to <literal>-</literal>.</para>
 181     </refsect2>
 182
 183     <refsect2>
 184       <title>ID</title>
 185
 186       <para>For <varname>u</varname> and <varname>g</varname>, the
 187       numeric 32-bit UID or GID of the user/group. Do not use IDs 65535
 188       or 4294967295, as they have special placeholder meanings.
 189       Specify <literal>-</literal> for automatic UID/GID allocation
 190       for the user or group (this is strongly recommended unless it is strictly
 191       necessary to use a specific UID or GID). Alternatively, specify an absolute path
 192       in the file system. In this case, the UID/GID is read from the
 193       path's owner/group. This is useful to create users whose UID/GID
 194       match the owners of pre-existing files (such as SUID or SGID
 195       binaries).
 196       The syntax <literal><replaceable>uid</replaceable>:<replaceable>gid</replaceable></literal> is also supported to
 197       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
 198       is also supported.
 199       </para>
 200
 201       <para>For <varname>m</varname> lines, this field should contain
 202       the group name to add to a user to.</para>
 203
 204       <para>For lines of type <varname>r</varname>, this field should
 205       be set to a UID/GID range in the format
 206       <literal>FROM-TO</literal>, where both values are formatted as
 207       decimal ASCII numbers. Alternatively, a single UID/GID may be
 208       specified formatted as decimal ASCII numbers.</para>
 209     </refsect2>
 210
 211     <refsect2>
 212       <title>GECOS</title>
 213
 214       <para>A short, descriptive string for users to be created, enclosed in
 215       quotation marks. Note that this field may not contain colons.</para>
 216
 217       <para>Only applies to lines of type <varname>u</varname> and should otherwise
 218       be left unset (or <literal>-</literal>).</para>
 219     </refsect2>
 220
 221     <refsect2>
 222       <title>Home Directory</title>
 223
 224       <para>The home directory for a new system user. If omitted, defaults to the
 225       root directory.</para>
 226
 227       <para>Only applies to lines of type <varname>u</varname> and should otherwise
 228       be left unset (or <literal>-</literal>). It is recommended to omit this, unless
 229       software strictly requires a home directory to be set.</para>
 230     </refsect2>
 231
 232     <refsect2>
 233       <title>Shell</title>
 234
 235       <para>The login shell of the user. If not specified, this will be set to
 236       <filename>/sbin/nologin</filename>, except if the UID of the user is 0, in
 237       which case <filename>/bin/sh</filename> will be used.</para>
 238
 239       <para>Only applies to lines of type <varname>u</varname> and should otherwise
 240       be left unset (or <literal>-</literal>). It is recommended to omit this, unless
 241       a shell different <filename>/sbin/nologin</filename> must be used.</para>
 242     </refsect2>
 243   </refsect1>
 244
 245   <refsect1>
 246     <title>Idempotence</title>
 247
 248     <para>Note that <command>systemd-sysusers</command> will do nothing if the
 249     specified users or groups already exist or the users are members of specified
 250     groups, so normally there is no reason to override
 251     <filename>sysusers.d</filename> vendor configuration, except to block certain
 252     users or groups from being created.</para>
 253   </refsect1>
 254
 255   <refsect1>
 256     <title>See Also</title>
 257     <para>
 258       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 259       <citerefentry><refentrytitle>systemd-sysusers</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 260     </para>
 261   </refsect1>
 262
 263 </refentry>