man/sysusers.d.xml

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<refentry id="sysusers.d" conditional='ENABLE_SYSUSERS'
    xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sysusers.d</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sysusers.d</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sysusers.d</refname>
    <refpurpose>Declarative allocation of system users and groups</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>/etc/sysusers.d/*.conf</filename></para>
    <para><filename>/run/sysusers.d/*.conf</filename></para>
    <para><filename>/usr/lib/sysusers.d/*.conf</filename></para>

    <programlisting>
#Type Name       ID                  GECOS              Home directory Shell
u     user_name  uid                 "User Description" /home/dir      /path/to/shell
u     user_name  uid:gid             "User Description" /home/dir      /path/to/shell
u     user_name  /file/owned/by/user "User Description" /home/dir      /path/to/shell
g     group_name gid
g     group_name /file/owned/by/group
m     user_name  group_name
r     -          lowest-highest</programlisting>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>systemd-sysusers</command> uses the files from
    <filename>sysusers.d</filename> directory to create system users and groups and
    to add users to groups, at package installation or boot time. This tool may be
    used to allocate system users and groups only, it is not useful for creating
    non-system (i.e. regular, "human") users and groups, as it accesses
    <filename>/etc/passwd</filename> and <filename>/etc/group</filename> directly,
    bypassing any more complex user databases, for example any database involving NIS
    or LDAP.</para>
  </refsect1>

  <refsect1>
    <title>Configuration Directories and Precedence</title>

    <para>Each configuration file shall be named in the style of
    <filename><replaceable>package</replaceable>.conf</filename> or
    <filename><replaceable>package</replaceable>-<replaceable>part</replaceable>.conf</filename>.
    The second variant should be used when it is desirable to make it
    easy to override just this part of configuration.</para>

    <para>Files in <filename>/etc/sysusers.d</filename> override files
    with the same name in <filename>/usr/lib/sysusers.d</filename> and
    <filename>/run/sysusers.d</filename>. Files in
    <filename>/run/sysusers.d</filename> override files with the same
    name in <filename>/usr/lib/sysusers.d</filename>. Packages should
    install their configuration files in
    <filename>/usr/lib/sysusers.d</filename>. Files in
    <filename>/etc/sysusers.d</filename> are reserved for the local
    administrator, who may use this logic to override the
    configuration files installed by vendor packages. All
    configuration files are sorted by their filename in lexicographic
    order, regardless of which of the directories they reside in. If
    multiple files specify the same path, the entry in the file with
    the lexicographically earliest name will be applied. All later
    entries for the same user and group names will be logged as warnings.
    </para>

    <para>If the administrator wants to disable a configuration file
    supplied by the vendor, the recommended way is to place a symlink
    to <filename>/dev/null</filename> in
    <filename>/etc/sysusers.d/</filename> bearing the same filename.
    </para>
  </refsect1>

  <refsect1>
    <title>Configuration File Format</title>

    <para>The file format is one line per user or group containing name, ID, GECOS
    field description, home directory, and login shell:</para>

    <programlisting>#Type Name     ID             GECOS                 Home directory Shell
u     httpd    404            "HTTP User"
u     _authd   /usr/bin/authd "Authorization user"
u     postgres -              "Postgresql Database" /var/lib/pgsql /usr/libexec/postgresdb
g     input    -              -
m     _authd   input
u     root     0              "Superuser"           /root          /bin/zsh
r     -        500-900
</programlisting>

    <para>Empty lines and lines beginning with the <literal>#</literal> character are ignored, and may be used for
    commenting.</para>

    <refsect2>
      <title>Type</title>

      <para>The type consists of a single letter. The following line
      types are understood:</para>

      <variablelist>
        <varlistentry>
          <term><varname>u</varname></term>
          <listitem><para>Create a system user and group of the specified name should
          they not exist yet. The user's primary group will be set to the group
          bearing the same name unless the ID field specifies it. The account will be
          created disabled, so that logins are not allowed.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>g</varname></term>
          <listitem><para>Create a system group of the specified name
          should it not exist yet. Note that <varname>u</varname>
          implicitly creates a matching group. The group will be
          created with no password set.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>m</varname></term>
          <listitem><para>Add a user to a group. If the user or group
          do not exist yet, they will be implicitly
          created.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><varname>r</varname></term>
          <listitem><para>Add a range of numeric UIDs/GIDs to the pool
          to allocate new UIDs and GIDs from. If no line of this type
          is specified, the range of UIDs/GIDs is set to some
          compiled-in default. Note that both UIDs and GIDs are
          allocated from the same pool, in order to ensure that users
          and groups of the same name are likely to carry the same
          numeric UID and GID.</para></listitem>
        </varlistentry>

      </variablelist>
    </refsect2>

    <refsect2>
      <title>Name</title>

      <para>The name field specifies the user or group name. The specified name must consist only of the characters a-z,
      A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character which must be one of a-z,
      A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted as first character). The
      user/group name must have at least one character, and at most 31.</para>

      <para>For further details about the syntax of user/group names, see <ulink
      url="https://systemd.io/USER_NAMES">User/Group Name Syntax</ulink>.</para>

      <para>It is strongly recommended to pick user and group names that are unlikely to clash with normal users
      created by the administrator. A good scheme to guarantee this is by prefixing all system and group names with the
      underscore, and avoiding too generic names.</para>

      <para>For <varname>m</varname> lines, this field should contain
      the user name to add to a group.</para>

      <para>For lines of type <varname>r</varname>, this field should
      be set to <literal>-</literal>.</para>
    </refsect2>

    <refsect2>
      <title>ID</title>

      <para>For <varname>u</varname> and <varname>g</varname>, the
      numeric 32-bit UID or GID of the user/group. Do not use IDs 65535
      or 4294967295, as they have special placeholder meanings.
      Specify <literal>-</literal> for automatic UID/GID allocation
      for the user or group (this is strongly recommended unless it is strictly
      necessary to use a specific UID or GID). Alternatively, specify an absolute path
      in the file system. In this case, the UID/GID is read from the
      path's owner/group. This is useful to create users whose UID/GID
      match the owners of pre-existing files (such as SUID or SGID
      binaries).
      The syntaxes <literal><replaceable>uid</replaceable>:<replaceable>gid</replaceable></literal> and
      <literal><replaceable>uid</replaceable>:<replaceable>groupname</replaceable></literal> are supported to
      allow creating users with specific primary groups. The given group must be created explicitly, or it
      must already exist. Specifying <literal>-</literal> for the UID in these syntaxes is also supported.
      </para>

      <para>For <varname>m</varname> lines, this field should contain
      the group name to add to a user to.</para>

      <para>For lines of type <varname>r</varname>, this field should
      be set to a UID/GID range in the format
      <literal>FROM-TO</literal>, where both values are formatted as
      decimal ASCII numbers. Alternatively, a single UID/GID may be
      specified formatted as decimal ASCII numbers.</para>
    </refsect2>

    <refsect2>
      <title>GECOS</title>

      <para>A short, descriptive string for users to be created, enclosed in
      quotation marks. Note that this field may not contain colons.</para>

      <para>Only applies to lines of type <varname>u</varname> and should otherwise
      be left unset (or <literal>-</literal>).</para>
    </refsect2>

    <refsect2>
      <title>Home Directory</title>

      <para>The home directory for a new system user. If omitted, defaults to the
      root directory.</para>

      <para>Only applies to lines of type <varname>u</varname> and should otherwise
      be left unset (or <literal>-</literal>). It is recommended to omit this, unless
      software strictly requires a home directory to be set.</para>
    </refsect2>

    <refsect2>
      <title>Shell</title>

      <para>The login shell of the user. If not specified, this will be set to
      <filename>/usr/sbin/nologin</filename>, except if the UID of the user is 0, in
      which case <filename>/bin/sh</filename> will be used.</para>

      <para>Only applies to lines of type <varname>u</varname> and should otherwise
      be left unset (or <literal>-</literal>). It is recommended to omit this, unless
      a shell different <filename>/usr/sbin/nologin</filename> must be used.</para>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Specifiers</title>

    <para>Specifiers can be used in the <literal>Name</literal>, <literal>ID</literal>,
    <literal>GECOS</literal>, <literal>Home directory</literal>, and <literal>Shell</literal> fields. An
    unknown or unresolvable specifier is treated as invalid configuration. The following expansions are
    understood:</para>

    <table class='specifiers'>
      <title>Specifiers available</title>
      <tgroup cols='3' align='left' colsep='1' rowsep='1'>
        <colspec colname="spec" />
        <colspec colname="mean" />
        <colspec colname="detail" />
        <thead>
          <row>
            <entry>Specifier</entry>
            <entry>Meaning</entry>
            <entry>Details</entry>
          </row>
        </thead>
        <tbody>
          <xi:include href="standard-specifiers.xml" xpointer="a"/>
          <xi:include href="standard-specifiers.xml" xpointer="b"/>
          <xi:include href="standard-specifiers.xml" xpointer="B"/>
          <xi:include href="standard-specifiers.xml" xpointer="H"/>
          <xi:include href="standard-specifiers.xml" xpointer="l"/>
          <xi:include href="standard-specifiers.xml" xpointer="m"/>
          <xi:include href="standard-specifiers.xml" xpointer="o"/>
          <xi:include href="standard-specifiers.xml" xpointer="T"/>
          <xi:include href="standard-specifiers.xml" xpointer="v"/>
          <xi:include href="standard-specifiers.xml" xpointer="V"/>
          <xi:include href="standard-specifiers.xml" xpointer="w"/>
          <xi:include href="standard-specifiers.xml" xpointer="W"/>
          <xi:include href="standard-specifiers.xml" xpointer="percent"/>
        </tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    <title>Idempotence</title>

    <para>Note that <command>systemd-sysusers</command> will do nothing if the
    specified users or groups already exist or the users are members of specified
    groups, so normally there is no reason to override
    <filename>sysusers.d</filename> vendor configuration, except to block certain
    users or groups from being created.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-sysusers</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>