man/sysusers.d.xml

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   7   Copyright 2014 Lennart Poettering
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  22 <refentry id="sysusers.d" conditional='ENABLE_SYSUSERS'
  23     xmlns:xi="http://www.w3.org/2001/XInclude">
  24
  25   <refentryinfo>
  26     <title>sysusers.d</title>
  27     <productname>systemd</productname>
  28
  29     <authorgroup>
  30       <author>
  31         <contrib>Developer</contrib>
  32         <firstname>Lennart</firstname>
  33         <surname>Poettering</surname>
  34         <email>lennart@poettering.net</email>
  35       </author>
  36     </authorgroup>
  37   </refentryinfo>
  38
  39   <refmeta>
  40     <refentrytitle>sysusers.d</refentrytitle>
  41     <manvolnum>5</manvolnum>
  42   </refmeta>
  43
  44   <refnamediv>
  45     <refname>sysusers.d</refname>
  46     <refpurpose>Declarative allocation of system users and groups</refpurpose>
  47   </refnamediv>
  48
  49   <refsynopsisdiv>
  50     <para><filename>/etc/sysusers.d/*.conf</filename></para>
  51     <para><filename>/run/sysusers.d/*.conf</filename></para>
  52     <para><filename>/usr/lib/sysusers.d/*.conf</filename></para>
  53   </refsynopsisdiv>
  54
  55   <refsect1>
  56     <title>Description</title>
  57
  58     <para><command>systemd-sysusers</command> uses the files from <filename>sysusers.d</filename> directory to create
  59     system users and groups at package installation or boot time. This tool may be used to allocate system users and
  60     groups only, it is not useful for creating non-system (i.e. regular, "human") users and groups, as it accesses
  61     <filename>/etc/passwd</filename> and <filename>/etc/group</filename> directly, bypassing any more complex user
  62     databases, for example any database involving NIS or LDAP.</para>
  63   </refsect1>
  64
  65   <refsect1>
  66     <title>Configuration Directories and Precedence</title>
  67
  68     <para>Each configuration file shall be named in the style of
  69     <filename><replaceable>package</replaceable>.conf</filename> or
  70     <filename><replaceable>package</replaceable>-<replaceable>part</replaceable>.conf</filename>.
  71     The second variant should be used when it is desirable to make it
  72     easy to override just this part of configuration.</para>
  73
  74     <para>Files in <filename>/etc/sysusers.d</filename> override files
  75     with the same name in <filename>/usr/lib/sysusers.d</filename> and
  76     <filename>/run/sysusers.d</filename>. Files in
  77     <filename>/run/sysusers.d</filename> override files with the same
  78     name in <filename>/usr/lib/sysusers.d</filename>. Packages should
  79     install their configuration files in
  80     <filename>/usr/lib/sysusers.d</filename>. Files in
  81     <filename>/etc/sysusers.d</filename> are reserved for the local
  82     administrator, who may use this logic to override the
  83     configuration files installed by vendor packages. All
  84     configuration files are sorted by their filename in lexicographic
  85     order, regardless of which of the directories they reside in. If
  86     multiple files specify the same path, the entry in the file with
  87     the lexicographically earliest name will be applied. All later
  88     entries for the same user and group names will be logged as warnings.
  89     </para>
  90
  91     <para>If the administrator wants to disable a configuration file
  92     supplied by the vendor, the recommended way is to place a symlink
  93     to <filename>/dev/null</filename> in
  94     <filename>/etc/sysusers.d/</filename> bearing the same filename.
  95     </para>
  96   </refsect1>
  97
  98   <refsect1>
  99     <title>Configuration File Format</title>
 100
 101     <para>The file format is one line per user or group containing
 102     name, ID, GECOS field description and home directory:</para>
 103
 104     <programlisting>#Type  Name   ID              GECOS                 Home directory
 105 u      httpd  440             "HTTP User"
 106 u      authd  /usr/bin/authd  "Authorization user"
 107 g      input  -               -
 108 m      authd  input
 109 u      root   0               "Superuser"           /root</programlisting>
 110
 111     <para>Empty lines and lines beginning with the <literal>#</literal> character are ignored, and may be used for
 112     commenting.</para>
 113
 114     <refsect2>
 115       <title>Type</title>
 116
 117       <para>The type consists of a single letter. The following line
 118       types are understood:</para>
 119
 120       <variablelist>
 121         <varlistentry>
 122           <term><varname>u</varname></term>
 123           <listitem><para>Create a system user and group of the
 124           specified name should they not exist yet. The user's primary
 125           group will be set to the group bearing the same name. The
 126           user's shell will be set to
 127           <filename>/sbin/nologin</filename>, the home directory to
 128           the specified home directory, or <filename>/</filename> if
 129           none is given. The account will be created disabled, so that
 130           logins are not allowed.</para></listitem>
 131         </varlistentry>
 132
 133         <varlistentry>
 134           <term><varname>g</varname></term>
 135           <listitem><para>Create a system group of the specified name
 136           should it not exist yet. Note that <varname>u</varname>
 137           implicitly create a matching group. The group will be
 138           created with no password set.</para></listitem>
 139         </varlistentry>
 140
 141         <varlistentry>
 142           <term><varname>m</varname></term>
 143           <listitem><para>Add a user to a group. If the user or group
 144           do not exist yet, they will be implicitly
 145           created.</para></listitem>
 146         </varlistentry>
 147
 148         <varlistentry>
 149           <term><varname>r</varname></term>
 150           <listitem><para>Add a range of numeric UIDs/GIDs to the pool
 151           to allocate new UIDs and GIDs from. If no line of this type
 152           is specified, the range of UIDs/GIDs is set to some
 153           compiled-in default. Note that both UIDs and GIDs are
 154           allocated from the same pool, in order to ensure that users
 155           and groups of the same name are likely to carry the same
 156           numeric UID and GID.</para></listitem>
 157         </varlistentry>
 158
 159       </variablelist>
 160     </refsect2>
 161
 162     <refsect2>
 163       <title>Name</title>
 164
 165       <para>The name field specifies the user or group name. The specified name must consist only of the characters a-z,
 166       A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character which must be one of a-z,
 167       A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted as first character). The
 168       user/group name must have at least one character, and at most 31.</para>
 169
 170       <para>It is strongly recommended to pick user and group names that are unlikely to clash with normal users
 171       created by the administrator. A good scheme to guarantee this is by prefixing all system and group names with the
 172       underscore, and avoiding too generic names.</para>
 173
 174       <para>For <varname>m</varname> lines, this field should contain
 175       the user name to add to a group.</para>
 176
 177       <para>For lines of type <varname>r</varname>, this field should
 178       be set to <literal>-</literal>.</para>
 179     </refsect2>
 180
 181     <refsect2>
 182       <title>ID</title>
 183
 184       <para>For <varname>u</varname> and <varname>g</varname>, the
 185       numeric 32-bit UID or GID of the user/group. Do not use IDs 65535
 186       or 4294967295, as they have special placeholder meanings.
 187       Specify <literal>-</literal> for automatic UID/GID allocation
 188       for the user or group. Alternatively, specify an absolute path
 189       in the file system. In this case, the UID/GID is read from the
 190       path's owner/group. This is useful to create users whose UID/GID
 191       match the owners of pre-existing files (such as SUID or SGID
 192       binaries).</para>
 193
 194       <para>For <varname>m</varname> lines, this field should contain
 195       the group name to add to a user to.</para>
 196
 197       <para>For lines of type <varname>r</varname>, this field should
 198       be set to a UID/GID range in the format
 199       <literal>FROM-TO</literal>, where both values are formatted as
 200       decimal ASCII numbers. Alternatively, a single UID/GID may be
 201       specified formatted as decimal ASCII numbers.</para>
 202     </refsect2>
 203
 204     <refsect2>
 205       <title>GECOS</title>
 206
 207       <para>A short, descriptive string for users to be created,
 208       enclosed in quotation marks. Note that this field may not
 209       contain colons.</para>
 210
 211       <para>Only applies to lines of type <varname>u</varname> and
 212       should otherwise be left unset, or be set to
 213       <literal>-</literal>.</para>
 214     </refsect2>
 215
 216     <refsect2>
 217       <title>Home Directory</title>
 218
 219       <para>The home directory for a new system user. If omitted,
 220       defaults to the root directory. It is recommended to not
 221       unnecessarily specify home directories for system users, unless
 222       software strictly requires one to be set.</para>
 223
 224       <para>Only applies to lines of type <varname>u</varname> and
 225       should otherwise be left unset, or be set to
 226       <literal>-</literal>.</para>
 227     </refsect2>
 228   </refsect1>
 229
 230   <refsect1>
 231     <title>Idempotence</title>
 232
 233     <para>Note that <command>systemd-sysusers</command> will do
 234     nothing if the specified users or groups already exist, so
 235     normally, there is no reason to override
 236     <filename>sysusers.d</filename> vendor configuration, except to
 237     block certain users or groups from being created.</para>
 238   </refsect1>
 239
 240   <refsect1>
 241     <title>See Also</title>
 242     <para>
 243       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 244       <citerefentry><refentrytitle>systemd-sysusers</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 245     </para>
 246   </refsect1>
 247
 248 </refentry>