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 <filename>sysusers.d</filename> directory to create
  61     system users and groups at package installation or boot time. This tool may be used to allocate system users and
  62     groups only, it is not useful for creating non-system (i.e. regular, "human") users and groups, as it accesses
  63     <filename>/etc/passwd</filename> and <filename>/etc/group</filename> directly, bypassing any more complex user
  64     databases, for example any database involving NIS or LDAP.</para>
  65   </refsect1>
  66
  67   <refsect1>
  68     <title>Configuration Directories and Precedence</title>
  69
  70     <para>Each configuration file shall be named in the style of
  71     <filename><replaceable>package</replaceable>.conf</filename> or
  72     <filename><replaceable>package</replaceable>-<replaceable>part</replaceable>.conf</filename>.
  73     The second variant should be used when it is desirable to make it
  74     easy to override just this part of configuration.</para>
  75
  76     <para>Files in <filename>/etc/sysusers.d</filename> override files
  77     with the same name in <filename>/usr/lib/sysusers.d</filename> and
  78     <filename>/run/sysusers.d</filename>. Files in
  79     <filename>/run/sysusers.d</filename> override files with the same
  80     name in <filename>/usr/lib/sysusers.d</filename>. Packages should
  81     install their configuration files in
  82     <filename>/usr/lib/sysusers.d</filename>. Files in
  83     <filename>/etc/sysusers.d</filename> are reserved for the local
  84     administrator, who may use this logic to override the
  85     configuration files installed by vendor packages. All
  86     configuration files are sorted by their filename in lexicographic
  87     order, regardless of which of the directories they reside in. If
  88     multiple files specify the same path, the entry in the file with
  89     the lexicographically earliest name will be applied. All later
  90     entries for the same user and group names will be logged as warnings.
  91     </para>
  92
  93     <para>If the administrator wants to disable a configuration file
  94     supplied by the vendor, the recommended way is to place a symlink
  95     to <filename>/dev/null</filename> in
  96     <filename>/etc/sysusers.d/</filename> bearing the same filename.
  97     </para>
  98   </refsect1>
  99
 100   <refsect1>
 101     <title>Configuration File Format</title>
 102
 103     <para>The file format is one line per user or group containing
 104     name, ID, GECOS field description and home directory:</para>
 105
 106     <programlisting>#Type  Name   ID              GECOS                 Home directory
 107 u      httpd  440             "HTTP User"
 108 u      authd  /usr/bin/authd  "Authorization user"
 109 g      input  -               -
 110 m      authd  input
 111 u      root   0               "Superuser"           /root</programlisting>
 112
 113     <para>Empty lines and lines beginning with the <literal>#</literal> character are ignored, and may be used for
 114     commenting.</para>
 115
 116     <refsect2>
 117       <title>Type</title>
 118
 119       <para>The type consists of a single letter. The following line
 120       types are understood:</para>
 121
 122       <variablelist>
 123         <varlistentry>
 124           <term><varname>u</varname></term>
 125           <listitem><para>Create a system user and group of the
 126           specified name should they not exist yet. The user's primary
 127           group will be set to the group bearing the same name. The
 128           user's shell will be set to
 129           <filename>/sbin/nologin</filename>, the home directory to
 130           the specified home directory, or <filename>/</filename> if
 131           none is given. The account will be created disabled, so that
 132           logins 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. Alternatively, specify an absolute path
 191       in the file system. In this case, the UID/GID is read from the
 192       path's owner/group. This is useful to create users whose UID/GID
 193       match the owners of pre-existing files (such as SUID or SGID
 194       binaries).</para>
 195
 196       <para>For <varname>m</varname> lines, this field should contain
 197       the group name to add to a user to.</para>
 198
 199       <para>For lines of type <varname>r</varname>, this field should
 200       be set to a UID/GID range in the format
 201       <literal>FROM-TO</literal>, where both values are formatted as
 202       decimal ASCII numbers. Alternatively, a single UID/GID may be
 203       specified formatted as decimal ASCII numbers.</para>
 204     </refsect2>
 205
 206     <refsect2>
 207       <title>GECOS</title>
 208
 209       <para>A short, descriptive string for users to be created,
 210       enclosed in quotation marks. Note that this field may not
 211       contain colons.</para>
 212
 213       <para>Only applies to lines of type <varname>u</varname> and
 214       should otherwise be left unset, or be set to
 215       <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,
 222       defaults to the root directory. It is recommended to not
 223       unnecessarily specify home directories for system users, unless
 224       software strictly requires one to be set.</para>
 225
 226       <para>Only applies to lines of type <varname>u</varname> and
 227       should otherwise be left unset, or be set to
 228       <literal>-</literal>.</para>
 229     </refsect2>
 230   </refsect1>
 231
 232   <refsect1>
 233     <title>Idempotence</title>
 234
 235     <para>Note that <command>systemd-sysusers</command> will do
 236     nothing if the specified users or groups already exist, so
 237     normally, there is no reason to override
 238     <filename>sysusers.d</filename> vendor configuration, except to
 239     block certain users or groups from being created.</para>
 240   </refsect1>
 241
 242   <refsect1>
 243     <title>See Also</title>
 244     <para>
 245       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 246       <citerefentry><refentrytitle>systemd-sysusers</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 247     </para>
 248   </refsect1>
 249
 250 </refentry>