dbus/doc/dbus-daemon.1.xml.in

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
                   "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<refentry id='dbusdaemon1'>

<!--  dbus&bsol;-daemon manual page.
 Copyright (C) 2003,2008 Red Hat, Inc. -->

<refmeta>
<refentrytitle>dbus-daemon</refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo class="manual">User Commands</refmiscinfo>
<refmiscinfo class="source">D-Bus</refmiscinfo>
<refmiscinfo class="version">@DBUS_VERSION@</refmiscinfo>
</refmeta>
<refnamediv>
<refname>dbus-daemon</refname>
<refpurpose>Message bus daemon</refpurpose>
</refnamediv>
<!-- body begins here -->
<refsynopsisdiv id='synopsis'>
<cmdsynopsis>
  <command>dbus-daemon</command></cmdsynopsis>
<cmdsynopsis>
  <command>dbus-daemon</command>    <arg choice='opt'>--version </arg>
    <arg choice='opt'>--session </arg>
    <arg choice='opt'>--system </arg>
    <arg choice='opt'>--config-file=<replaceable>FILE</replaceable></arg>
    <arg choice='opt'><arg choice='plain'>--print-address </arg><arg choice='opt'><replaceable>=DESCRIPTOR</replaceable></arg></arg>
    <arg choice='opt'><arg choice='plain'>--print-pid </arg><arg choice='opt'><replaceable>=DESCRIPTOR</replaceable></arg></arg>
    <arg choice='opt'>--fork </arg>
    <arg choice='opt'>--nosyslog </arg>
    <arg choice='opt'>--syslog </arg>
    <arg choice='opt'>--syslog-only </arg>
    <sbr/>
</cmdsynopsis>
</refsynopsisdiv>


<refsect1 id='description'><title>DESCRIPTION</title>
<para><command>dbus-daemon</command> is the D-Bus message bus daemon. See
<ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink> for more information about
the big picture. D-Bus is first a library that provides one-to-one
communication between any two applications; <command>dbus-daemon</command> is an
application that uses this library to implement a message bus
daemon. Multiple programs connect to the message bus daemon and can
exchange messages with one another.</para>

<para>There are two standard message bus instances: the systemwide message bus
(installed on many systems as the "messagebus" init service) and the
per-user-login-session message bus (started each time a user logs in).
<command>dbus-daemon</command> is used for both of these instances, but with
a different configuration file.</para>

<para>The --session option is equivalent to
"--config-file=@EXPANDED_DATADIR@/dbus-1/session.conf" and the --system
option is equivalent to
"--config-file=@EXPANDED_DATADIR@/dbus-1/system.conf". By creating
additional configuration files and using the --config-file option,
additional special-purpose message bus daemons could be created.</para>

<para>The systemwide daemon is normally launched by an init script,
standardly called simply "messagebus".</para>

<para>The systemwide daemon is largely used for broadcasting system events,
such as changes to the printer queue, or adding/removing devices.</para>

<para>The per-session daemon is used for various interprocess communication
among desktop applications (however, it is not tied to X or the GUI
in any way).</para>

<para>SIGHUP will cause the D-Bus daemon to PARTIALLY reload its
configuration file and to flush its user/group information caches. Some
configuration changes would require kicking all apps off the bus; so they will
only take effect if you restart the daemon. Policy changes should take effect
with SIGHUP.</para>

</refsect1>

<refsect1 id='options'><title>OPTIONS</title>
<para>The following options are supported:</para>
<variablelist remap='TP'>
  <varlistentry>
  <term><option>--config-file=FILE</option></term>
  <listitem>
<para>Use the given configuration file.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--fork</option></term>
  <listitem>
<para>Force the message bus to fork and become a daemon, even if
the configuration file does not specify that it should.
In most contexts the configuration file already gets this
right, though. This option is not supported on Windows.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--nofork</option></term>
  <listitem>
    <para>Force the message bus not to fork and become a daemon, even if
      the configuration file specifies that it should. On Windows,
      the dbus-daemon never forks, so this option is allowed but does
      nothing.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--print-address[=DESCRIPTOR]</option></term>
  <listitem>
<para>Print the address of the message bus to standard output, or
to the given file descriptor. This is used by programs that
launch the message bus.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--print-pid[=DESCRIPTOR]</option></term>
  <listitem>
<para>Print the process ID of the message bus to standard output, or
to the given file descriptor. This is used by programs that
launch the message bus.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--session</option></term>
  <listitem>
<para>Use the standard configuration file for the per-login-session message
bus.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--system</option></term>
  <listitem>
<para>Use the standard configuration file for the systemwide message bus.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--version</option></term>
  <listitem>
<para>Print the version of the daemon.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--introspect</option></term>
  <listitem>
<para>Print the introspection information for all D-Bus internal interfaces.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--address[=ADDRESS]</option></term>
  <listitem>
    <para>Set the address to listen on. This option overrides the address
      configured in the configuration file via the
      <literal>&lt;listen&gt;</literal> directive.
      See the documentation of that directive for more details.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--systemd-activation</option></term>
  <listitem>
<para>Enable systemd-style service activation. Only useful in conjunction
with the systemd system and session manager on Linux.</para>
  </listitem>
  </varlistentry>
  <varlistentry>
  <term><option>--nopidfile</option></term>
  <listitem>
<para>Don't write a PID file even if one is configured in the configuration
files.</para>

  </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--syslog</option></term>
    <listitem>
      <para>Force the message bus to use the system log for messages,
        in addition to writing to standard error, even if the configuration
        file does not specify that it should. On Unix, this uses
        the syslog; on Windows, this uses OutputDebugString().</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--syslog-only</option></term>
    <listitem>
      <para>Force the message bus to use the system log for messages,
        and <emphasis>not</emphasis> duplicate them to standard error.
        On Unix, this uses the syslog; on Windows, this uses
        OutputDebugString().</para>
    </listitem>
  </varlistentry>

  <varlistentry>
    <term><option>--nosyslog</option></term>
    <listitem>
      <para>Force the message bus to use only standard error for messages,
        even if the configuration file specifies that it should use
        the system log.</para>
    </listitem>
  </varlistentry>

</variablelist>
</refsect1>

<refsect1 id='configuration_file'><title>CONFIGURATION FILE</title>
<para>A message bus daemon has a configuration file that specializes it
for a particular application. For example, one configuration
file might set up the message bus to be a systemwide message bus,
while another might set it up to be a per-user-login-session bus.</para>

<para>The configuration file also establishes resource limits, security
parameters, and so forth.</para>

<para>The configuration file is not part of any interoperability
specification and its backward compatibility is not guaranteed; this
document is documentation, not specification.</para>

<para>The standard systemwide and per-session message bus setups are
configured in the files "@EXPANDED_DATADIR@/dbus-1/system.conf" and
"@EXPANDED_DATADIR@/dbus-1/session.conf".  These files normally
&lt;include&gt; a system-local.conf or session-local.conf in
@EXPANDED_SYSCONFDIR@/dbus-1; you can put local
overrides in those files to avoid modifying the primary configuration
files.</para>


<para>The configuration file is an XML document. It must have the following
doctype declaration:</para>
<literallayout remap='.nf'>

   &lt;!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
    "<ulink url='http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd'>http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd</ulink>"&gt;

</literallayout> <!-- .fi -->


<para>The following elements may be present in the configuration file.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;busconfig&gt;</emphasis></para></listitem>


</itemizedlist>

<para>Root element.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;type&gt;</emphasis></para></listitem>


</itemizedlist>

<para>The well-known type of the message bus. Currently known values are
"system" and "session"; if other values are set, they should be
either added to the D-Bus specification, or namespaced.  The last
&lt;type&gt; element "wins" (previous values are ignored). This element
only controls which message bus specific environment variables are
set in activated clients.  Most of the policy that distinguishes a
session bus from the system bus is controlled from the other elements
in the configuration file.</para>


<para>If the well-known type of the message bus is "session", then the
DBUS_STARTER_BUS_TYPE environment variable will be set to "session"
and the DBUS_SESSION_BUS_ADDRESS environment variable will be set
to the address of the session bus.  Likewise, if the type of the
message bus is "system", then the DBUS_STARTER_BUS_TYPE environment
variable will be set to "system" and the DBUS_SESSION_BUS_ADDRESS
environment variable will be set to the address of the system bus
(which is normally well known anyway).</para>


<para>Example: &lt;type&gt;session&lt;/type&gt;</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;include&gt;</emphasis></para></listitem>


</itemizedlist>

<para>Include a file &lt;include&gt;filename.conf&lt;/include&gt; at this point.  If the
filename is relative, it is located relative to the configuration file
doing the including.</para>


<para>&lt;include&gt; has an optional attribute "ignore_missing=(yes|no)"
which defaults to "no" if not provided. This attribute
controls whether it's a fatal error for the included file
to be absent.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;includedir&gt;</emphasis></para></listitem>


</itemizedlist>

<para>Include all files in &lt;includedir&gt;foo.d&lt;/includedir&gt; at this
point. Files in the directory are included in undefined order.
Only files ending in ".conf" are included.</para>


<para>This is intended to allow extension of the system bus by particular
packages. For example, if CUPS wants to be able to send out
notification of printer queue changes, it could install a file to
@EXPANDED_DATADIR@/dbus-1/system.d or
@EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
this message and allowed the printer daemon user to send it.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;user&gt;</emphasis></para></listitem>


</itemizedlist>

<para>The user account the daemon should run as, as either a username or a
UID. If the daemon cannot change to this UID on startup, it will exit.
If this element is not present, the daemon will not change or care
about its UID.</para>


<para>The last &lt;user&gt; entry in the file "wins", the others are ignored.</para>


<para>The user is changed after the bus has completed initialization.  So
sockets etc. will be created before changing user, but no data will be
read from clients before changing user. This means that sockets
and PID files can be created in a location that requires root
privileges for writing.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;fork&gt;</emphasis></para></listitem>


</itemizedlist>

<para>If present, the bus daemon becomes a real daemon (forks
into the background, etc.). This is generally used
rather than the --fork command line option.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;keep_umask&gt;</emphasis></para></listitem>


</itemizedlist>

<para>If present, the bus daemon keeps its original umask when forking.
This may be useful to avoid affecting the behavior of child processes.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;syslog&gt;</emphasis></para></listitem>


</itemizedlist>

<para>If present, the bus daemon will log to syslog. The
  --syslog, --syslog-only and --nosyslog command-line options take precedence
  over this setting.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;pidfile&gt;</emphasis></para></listitem>


</itemizedlist>

<para>If present, the bus daemon will write its pid to the specified file.
The --nopidfile command-line option takes precedence over this setting.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;allow_anonymous&gt;</emphasis></para></listitem>


</itemizedlist>

<para>If present, connections that authenticated using the ANONYMOUS
mechanism will be authorized to connect. This option has no practical
effect unless the ANONYMOUS mechanism has also been enabled using the
<emphasis remap='I'>&lt;auth&gt;</emphasis> element, described below.</para>

<para>Using this directive in the configuration of the well-known
  system bus or the well-known session bus will make that bus insecure
  and should never be done. Similarly, on custom bus types, using this
  directive will usually make the custom bus insecure, unless its
  configuration has been specifically designed to prevent anonymous
  users from causing damage or escalating privileges.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;listen&gt;</emphasis></para></listitem>


</itemizedlist>

<para>Add an address that the bus should listen on. The
address is in the standard D-Bus format that contains
a transport name plus possible parameters/options.</para>

<para>On platforms other than Windows, <literal>unix</literal>-based
  transports (<literal>unix</literal>, <literal>systemd</literal>,
  <literal>launchd</literal>) are the default for both the well-known
  system bus and the well-known session bus, and are strongly
  recommended.</para>

<para>
  On Windows, <literal>unix</literal>-based transports are not available,
  so TCP-based transports must be used.
  Similar to remote X11, the <literal>tcp</literal> and
  <literal>nonce-tcp</literal> transports have no integrity or
  confidentiality protection, so they should normally only be
  used across the local loopback interface, for example using an
  address like <literal>tcp:host=127.0.0.1</literal> or
  <literal>nonce-tcp:host=localhost</literal>. In particular,
  configuring the well-known system bus or the well-known session
  bus to listen on a non-loopback TCP address is insecure.
</para>
<para>
  Developers are sometimes tempted to use remote TCP as a debugging
  tool. However, if this functionality is left enabled in finished
  products, the result will be dangerously insecure. Instead of
  using remote TCP, developers should <ulink
    url="https://lists.freedesktop.org/archives/dbus/2018-April/017447.html"
    >relay connections via Secure Shell or a similar protocol</ulink>.
  <!-- TODO: Ideally someone would write a more formal guide to
       remote D-Bus debugging, and we could link to that instead -->
</para>
<para>
  Remote TCP connections were historically sometimes used to share
  a single session bus between login sessions of the same user on
  different machines within a trusted local area network, in
  conjunction with unencrypted remote X11, a NFS-shared home
  directory and NIS (YP) authentication. This is insecure against
  an attacker on the same LAN and should be considered strongly
  deprecated; more specifically, it is insecure in the same ways
  and for the same reasons as unencrypted remote X11 and NFSv2/NFSv3.
  The D-Bus maintainers
  recommend using a separate session bus per (user, machine) pair,
  only accessible from within that machine.
</para>

<para>Example: &lt;listen&gt;unix:path=/tmp/foo&lt;/listen&gt;</para>


<para>Example: &lt;listen&gt;tcp:host=localhost,port=1234&lt;/listen&gt;</para>


<para>If there are multiple &lt;listen&gt; elements, then the bus listens
on multiple addresses. The bus will pass its address to
started services or other interested parties with
the last address given in &lt;listen&gt; first. That is,
apps will try to connect to the last &lt;listen&gt; address first.</para>


<para>tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.
If a hostname resolves to multiple addresses, the server will bind
to all of them. The family=ipv4 or family=ipv6 options can be used
to force it to bind to a subset of addresses</para>


<para>Example: &lt;listen&gt;tcp:host=localhost,port=0,family=ipv4&lt;/listen&gt;</para>


<para>A special case is using a port number of zero (or omitting the port),
which means to choose an available port selected by the operating
system. The port number chosen can be obtained with the
--print-address command line parameter and will be present in other
cases where the server reports its own address, such as when
DBUS_SESSION_BUS_ADDRESS is set.</para>


<para>Example: &lt;listen&gt;tcp:host=localhost,port=0&lt;/listen&gt;</para>


<para>tcp/nonce-tcp addresses also allow a bind=hostname option,
used in a listenable address to configure the interface on which
the server will listen: either the hostname is the IP address of
one of the local machine's interfaces (most commonly 127.0.0.1),
a DNS name that resolves to one of those IP addresses, '0.0.0.0'
to listen on all IPv4 interfaces simultaneously, or '::'
to listen on all IPv4 and IPv6 interfaces simultaneously (if supported
by the OS).  If not specified,
the default is the same value as "host".</para>


<para>Example: &lt;listen&gt;tcp:host=localhost,bind=0.0.0.0,port=0&lt;/listen&gt;</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;auth&gt;</emphasis></para></listitem>


</itemizedlist>

<para>Lists permitted authorization mechanisms. If this element doesn't
exist, then all known mechanisms are allowed.  If there are multiple
&lt;auth&gt; elements, all the listed mechanisms are allowed.  The order in
which mechanisms are listed is not meaningful.</para>

<para>On non-Windows operating systems, allowing only the
  <literal>EXTERNAL</literal> authentication
  mechanism is strongly recommended. This is the default for the
  well-known system bus and for the well-known session bus.</para>

<para>Example: &lt;auth&gt;EXTERNAL&lt;/auth&gt;</para>


<para>Example: &lt;auth&gt;DBUS_COOKIE_SHA1&lt;/auth&gt;</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;servicedir&gt;</emphasis></para></listitem>


</itemizedlist>

<para>
  Adds a directory to search for .service files, which tell the
  dbus-daemon how to start a program to provide a particular well-known
  bus name. See the D-Bus Specification for more details about the
  contents of .service files.
</para>

<para>
  If a particular service is found in more than one &lt;servicedir&gt;,
  the first directory listed in the configuration file takes precedence.
  If two service files providing the same well-known bus name are found
  in the same directory, it is arbitrary which one will be chosen
  (this can only happen if at least one of the service files does not
  have the recommended name, which is its well-known bus name followed
  by ".service").
</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;standard_session_servicedirs/&gt;</emphasis></para></listitem>


</itemizedlist>

<para>
  &lt;standard_session_servicedirs/&gt; requests a standard set of
  session service directories. Its effect is similar to specifying a series
  of &lt;servicedir/&gt; elements for each of the data directories,
  in the order given here.
  It is not exactly equivalent, because there is currently no way
  to disable directory monitoring or enforce strict service file naming
  for a &lt;servicedir/&gt;.
</para>

<para>
  As with &lt;servicedir/&gt; elements, if a particular service is found
  in more than one service directory, the first directory takes precedence.
  If two service files providing the same well-known bus name are found
  in the same directory, it is arbitrary which one will be chosen
  (this can only happen if at least one of the service files does not
  have the recommended name, which is its well-known bus name followed
  by ".service").
</para>

<para>
  On Unix, the standard session service directories are:
  <itemizedlist>
    <listitem>
      <para>
        <emphasis>$XDG_RUNTIME_DIR</emphasis>/dbus-1/services,
        if XDG_RUNTIME_DIR is set (see the XDG Base Directory
        Specification for details of XDG_RUNTIME_DIR):
        this location is suitable for transient services created at runtime
        by systemd generators (see
        <citerefentry>
          <refentrytitle>systemd.generator</refentrytitle>
          <manvolnum>7</manvolnum>
        </citerefentry>),
        session managers or other session infrastructure.
        It is an extension provided by the reference implementation
        of dbus-daemon, and is not standardized in the D-Bus Specification.
      </para>
      <para>
        Unlike the other standard session service directories, this directory
        enforces strict naming for the service files: the filename must be
        exactly the well-known bus name of the service, followed by
        ".service".
      </para>
      <para>
        Also unlike the other standard session service directories, this
        directory is never monitored with
        <citerefentry>
          <refentrytitle>inotify</refentrytitle>
          <manvolnum>7</manvolnum>
        </citerefentry>
        or similar APIs. Programs that create service files in this directory
        while a dbus-daemon is running are expected to call the dbus-daemon's
        ReloadConfig() method after they have made changes.
      </para>
    </listitem>
    <listitem>
      <para>
        <emphasis>$XDG_DATA_HOME</emphasis>/dbus-1/services,
        where XDG_DATA_HOME defaults to ~/.local/share
        (see the XDG Base Directory Specification): this location is
        specified by the D-Bus Specification, and is suitable for per-user,
        locally-installed software.
      </para>
    </listitem>
    <listitem>
      <para>
        <emphasis>directory</emphasis>/dbus-1/services for each
        directory in XDG_DATA_DIRS, where XDG_DATA_DIRS defaults to
        /usr/local/share:/usr/share
        (see the XDG Base Directory Specification): these locations are
        specified by the D-Bus Specification. The defaults are suitable
        for software installed locally by a system administrator
        (/usr/local/share) or for software installed from operating system
        packages (/usr/share). Per-user or system-wide configuration that
        sets the XDG_DATA_DIRS environment variable can extend this search
        path to cover installations in other locations, for example
        ~/.local/share/flatpak/exports/share/ and
        /var/lib/flatpak/exports/share/ when
        <citerefentry>
          <refentrytitle>flatpak</refentrytitle>
          <manvolnum>1</manvolnum>
        </citerefentry>
        is used.
      </para>
    </listitem>
    <listitem>
      <para>
        <emphasis>${datadir}</emphasis>/dbus-1/services
        for the <emphasis>${datadir}</emphasis> that was specified when
        dbus was compiled, typically /usr/share: this location is an
        extension provided by the reference dbus-daemon implementation,
        and is suitable for software stacks installed alongside dbus-daemon.
      </para>
    </listitem>
  </itemizedlist>
</para>

<para>The "XDG Base Directory Specification" can be found at
<ulink url='http://freedesktop.org/wiki/Standards/basedir-spec'>http://freedesktop.org/wiki/Standards/basedir-spec</ulink> if it hasn't moved,
otherwise try your favorite search engine.</para>

<para>
  On Windows, the standard session service directories are:
  <itemizedlist>
    <listitem>
      <para>
        <emphasis>%CommonProgramFiles%</emphasis>/dbus-1/services
        if %CommonProgramFiles% is set: this location is suitable for
        system-wide installed software packages
      </para>
    </listitem>
    <listitem>
      <para>
        A share/dbus-1/services directory found in the same
        directory hierarchy (prefix) as the dbus-daemon: this location
        is suitable for software stacks installed alongside dbus-daemon
      </para>
    </listitem>
  </itemizedlist>
</para>


<para>The &lt;standard_session_servicedirs/&gt; option is only relevant to the
per-user-session bus daemon defined in
@EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
configuration file would probably be nonsense.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;standard_system_servicedirs/&gt;</emphasis></para></listitem>


</itemizedlist>

<para>&lt;standard_system_servicedirs/&gt; specifies the standard system-wide
  activation directories that should be searched for service files.
  As with session services, the first directory listed has highest
  precedence.</para>

<para>
  On Unix, the standard session service directories are:
  <itemizedlist>
    <listitem>
      <para>
        /usr/local/share/dbus-1/system-services: this location is
        specified by the D-Bus Specification, and is suitable for
        software installed locally by the system administrator
      </para>
    </listitem>
    <listitem>
      <para>
        /usr/share/dbus-1/system-services: this location is
        specified by the D-Bus Specification, and is suitable for
        software installed by operating system packages
      </para>
    </listitem>
    <listitem>
      <para>
        <emphasis>${datadir}</emphasis>/dbus-1/system-services
        for the <emphasis>${datadir}</emphasis> that was specified when
        dbus was compiled, typically /usr/share: this location is an
        extension provided by the reference dbus-daemon implementation,
        and is suitable for software stacks installed alongside dbus-daemon
      </para>
    </listitem>
    <listitem>
      <para>
        /lib/dbus-1/system-services: this location is
        specified by the D-Bus Specification, and was intended for
        software installed by operating system packages and used during
        early boot (but it should be considered deprecated, because
        the reference dbus-daemon is not designed to be available during
        early boot)
      </para>
    </listitem>
  </itemizedlist>
</para>

<para>
  On Windows, there is no standard system bus, so there are no standard
  system bus directories either.
</para>

<para>The &lt;standard_system_servicedirs/&gt; option is only relevant to the
per-system bus daemon defined in
@EXPANDED_DATADIR@/dbus-1/system.conf. Putting it in any other
configuration file would probably be nonsense.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;servicehelper/&gt;</emphasis></para></listitem>


</itemizedlist>

<para>&lt;servicehelper/&gt; specifies the setuid helper that is used to launch
system daemons with an alternate user. Typically this should be
the dbus-daemon-launch-helper executable in located in libexec.</para>


<para>The &lt;servicehelper/&gt; option is only relevant to the per-system bus daemon
defined in @EXPANDED_DATADIR@/dbus-1/system.conf. Putting it in any other
configuration file would probably be nonsense.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;limit&gt;</emphasis></para></listitem>


</itemizedlist>

<para>&lt;limit&gt; establishes a resource limit. For example:</para>
<literallayout remap='.nf'>
  &lt;limit name="max_message_size"&gt;64&lt;/limit&gt;
  &lt;limit name="max_completed_connections"&gt;512&lt;/limit&gt;
</literallayout> <!-- .fi -->


<para>The name attribute is mandatory.
Available limit names are:</para>
<literallayout remap='.nf'>
      "max_incoming_bytes"         : total size in bytes of messages
                                     incoming from a single connection
      "max_incoming_unix_fds"      : total number of unix fds of messages
                                     incoming from a single connection
      "max_outgoing_bytes"         : total size in bytes of messages
                                     queued up for a single connection
      "max_outgoing_unix_fds"      : total number of unix fds of messages
                                     queued up for a single connection
      "max_message_size"           : max size of a single message in
                                     bytes
      "max_message_unix_fds"       : max unix fds of a single message
      "service_start_timeout"      : milliseconds (thousandths) until
                                     a started service has to connect
      "auth_timeout"               : milliseconds (thousandths) a
                                     connection is given to
                                     authenticate
      "pending_fd_timeout"         : milliseconds (thousandths) a
                                     fd is given to be transmitted to
                                     dbus-daemon before disconnecting the
                                     connection
      "max_completed_connections"  : max number of authenticated connections
      "max_incomplete_connections" : max number of unauthenticated
                                     connections
      "max_connections_per_user"   : max number of completed connections from
                                     the same user (only enforced on Unix OSs)
      "max_pending_service_starts" : max number of service launches in
                                     progress at the same time
      "max_names_per_connection"   : max number of names a single
                                     connection can own
      "max_match_rules_per_connection": max number of match rules for a single
                                        connection
      "max_replies_per_connection" : max number of pending method
                                     replies per connection
                                     (number of calls-in-progress)
      "reply_timeout"              : milliseconds (thousandths)
                                     until a method call times out
      "max_containers"             : max number of restricted servers for use
                                     in app-containers, in total
      "max_containers_per_user"    : max number of app-containers per Unix uid
      "max_container_metadata_bytes": max number of bytes of metadata to store
                                      for each app-container
      "max_connections_per_container": max number of (authenticated or
                                       unauthenticated) connections to each
                                       app-container
</literallayout> <!-- .fi -->


<para>The max incoming/outgoing queue sizes allow a new message to be queued
if one byte remains below the max. So you can in fact exceed the max
by max_message_size.</para>


<para>max_completed_connections divided by max_connections_per_user is the
number of users that can work together to denial-of-service all other users by using
up all connections on the systemwide bus.</para>


<para>Limits are normally only of interest on the systemwide bus, not the user session
buses.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;policy&gt;</emphasis></para></listitem>


</itemizedlist>

<para>The &lt;policy&gt; element defines a security policy to be applied to a particular
set of connections to the bus. A policy is made up of
&lt;allow&gt; and &lt;deny&gt; elements. Policies are normally used with the systemwide bus;
they are analogous to a firewall in that they allow expected traffic
and prevent unexpected traffic.</para>


<para>
  Currently, the system bus has a default-deny policy for sending method calls
  and owning bus names, and a default-allow policy for receiving messages,
  sending signals, and sending a single success or error reply for each
  method call that does not have the <literal>NO_REPLY</literal> flag.
  Sending more than the expected number of replies is not allowed.
</para>


<para>In general, it is best to keep system services as small, targeted programs which
run in their own process and provide a single bus name.  Then, all that is needed
is an &lt;allow&gt; rule for the "own" permission to let the process claim the bus
name, and a "send_destination" rule to allow traffic from some or all uids to
your service.</para>


<para>The &lt;policy&gt; element has one of four attributes:</para>
<literallayout remap='.nf'>
  context="(default|mandatory)"
  at_console="(true|false)"
  user="username or userid"
  group="group name or gid"
</literallayout> <!-- .fi -->


<para>Policies are applied to a connection as follows:</para>
<literallayout remap='.nf'>
   - all context="default" policies are applied
   - all group="connection's user's group" policies are applied
     in undefined order
   - all user="connection's auth user" policies are applied
     in undefined order
   - all at_console="true" policies are applied
   - all at_console="false" policies are applied
   - all context="mandatory" policies are applied
</literallayout> <!-- .fi -->


<para>Policies applied later will override those applied earlier,
when the policies overlap. Multiple policies with the same
user/group/context are applied in the order they appear
in the config file.</para>

<variablelist remap='TP'>
  <varlistentry>
  <term><emphasis remap='I'>&lt;deny&gt;</emphasis></term>
  <listitem>
<para><emphasis remap='I'>&lt;allow&gt;</emphasis></para>

  </listitem>
  </varlistentry>
</variablelist>

<para>A &lt;deny&gt; element appears below a &lt;policy&gt; element and prohibits some
action. The &lt;allow&gt; element makes an exception to previous &lt;deny&gt;
statements, and works just like &lt;deny&gt; but with the inverse meaning.</para>


<para>The possible attributes of these elements are:</para>
<literallayout remap='.nf'>
   send_interface="interface_name" | "*"
   send_member="method_or_signal_name" | "*"
   send_error="error_name" | "*"
   send_broadcast="true" | "false"
   send_destination="name" | "*"
   send_type="method_call" | "method_return" | "signal" | "error" | "*"
   send_path="/path/name" | "*"

   receive_interface="interface_name" | "*"
   receive_member="method_or_signal_name" | "*"
   receive_error="error_name" | "*"
   receive_sender="name" | "*"
   receive_type="method_call" | "method_return" | "signal" | "error" | "*"
   receive_path="/path/name" | "*"

   send_requested_reply="true" | "false"
   receive_requested_reply="true" | "false"

   eavesdrop="true" | "false"

   own="name" | "*"
   own_prefix="name"
   user="username" | "*"
   group="groupname" | "*"
</literallayout> <!-- .fi -->


<para>Examples:</para>
<literallayout remap='.nf'>
   &lt;deny send_destination="org.freedesktop.Service" send_interface="org.freedesktop.System" send_member="Reboot"/&gt;
   &lt;deny send_destination="org.freedesktop.System"/&gt;
   &lt;deny receive_sender="org.freedesktop.System"/&gt;
   &lt;deny user="john"/&gt;
   &lt;deny group="enemies"/&gt;
</literallayout> <!-- .fi -->


<para>The &lt;deny&gt; element's attributes determine whether the deny "matches" a
particular action. If it matches, the action is denied (unless later
rules in the config file allow it).</para>

<para>
  Rules with one or more of the <literal>send_</literal>* family of attributes
  are checked in order when a connection attempts to send a message. The last
  rule that matches the message determines whether it may be sent.
  The well-known session bus normally allows sending any message.
  The well-known system bus normally allows sending any signal, selected
  method calls to the <command>dbus-daemon</command>, and exactly one
  reply to each previously-sent method call (either success or an error).
  Either of these can be overridden by configuration; on the system bus,
  services that will receive method calls must install configuration that
  allows them to do so, usually via rules of the form
  <literal>&lt;policy context="default"&gt;&lt;allow send_destination="&hellip;"/&gt;&lt;policy&gt;</literal>.
</para>

<para>
  Rules with one or more of the <literal>receive_</literal>* family of
  attributes, or with the <literal>eavesdrop</literal> attribute and no others,
  are checked for each recipient of a message (there might be more than one
  recipient if the message is a broadcast or a connection is eavesdropping).
  The last rule that matches the message determines whether it may be received.
  The well-known session bus normally allows receiving any message, including
  eavesdropping. The well-known system bus normally allows receiving any
  message that was not eavesdropped (any unicast message addressed to the
  recipient, and any broadcast message).
</para>

<para>
  The <literal>eavesdrop</literal>, <literal>min_fds</literal> and
  <literal>max_fds</literal> attributes are modifiers that can be applied
  to either <literal>send_</literal>* or <literal>receive_</literal>*
  rules, and are documented below.
</para>

<para>send_destination and receive_sender rules mean that messages may not be
sent to or received from the *owner* of the given name, not that
they may not be sent *to that name*. That is, if a connection
owns services A, B, C, and sending to A is denied, sending to B or C
will not work either. As a special case,
<literal>send_destination="*"</literal> matches any message
(whether it has a destination specified or not), and
<literal>receive_sender="*"</literal> similarly matches any message.</para>

<para>
  Rules with <literal>send_broadcast="true"</literal> match signal messages
  with no destination (broadcasts). Rules with
  <literal>send_broadcast="false"</literal> are the inverse: they match any
  unicast destination (unicast signals, together with all method calls, replies
  and errors) but do not match messages with no destination (broadcasts). This
  is not the same as <literal>send_destination="*"</literal>, which matches any
  sent message, regardless of whether it has a destination or not.
</para>

<para>
  The other <literal>send_</literal>* and <literal>receive_</literal>*
  attributes are purely textual/by-value matches against the given field in
  the message header, except that for the attributes where it is allowed,
  <literal>*</literal> matches any message (whether it has the relevant
  header field or not). For example, <literal>send_interface="*"</literal>
  matches any sent message, even if it does not contain an interface header
  field. More complex glob matching such as <literal>foo.bar.*</literal> is
  not allowed.
</para>

<para>"Eavesdropping" occurs when an application receives a message that
was explicitly addressed to a name the application does not own, or
is a reply to such a message. Eavesdropping thus only applies to
messages that are addressed to services and replies to such messages
(i.e. it does not apply to signals).</para>

<para>For &lt;allow&gt;, eavesdrop="true" indicates that the rule matches even
when eavesdropping. eavesdrop="false" is the default and means that
the rule only allows messages to go to their specified recipient.
For &lt;deny&gt;, eavesdrop="true" indicates that the rule matches
only when eavesdropping. eavesdrop="false" is the default for &lt;deny&gt;
also, but here it means that the rule applies always, even when
not eavesdropping. The eavesdrop attribute can only be combined with
send and receive rules (with send_* and receive_* attributes).</para>

<para>The [send|receive]_requested_reply attribute works similarly to the eavesdrop
attribute. It controls whether the &lt;deny&gt; or &lt;allow&gt; matches a reply
that is expected (corresponds to a previous method call message).
This attribute only makes sense for reply messages (errors and method
returns), and is ignored for other message types.</para>


<para>For &lt;allow&gt;, [send|receive]_requested_reply="true" is the default and indicates that
only requested replies are allowed by the
rule. [send|receive]_requested_reply="false" means that the rule allows any reply
even if unexpected.</para>


<para>For &lt;deny&gt;, [send|receive]_requested_reply="false" is the default but indicates that
the rule matches only when the reply was not
requested. [send|receive]_requested_reply="true" indicates that the rule applies
always, regardless of pending reply state.</para>

<para>
  The <literal>min_fds</literal> and <literal>max_fds</literal> attributes
  modify either <literal>send_</literal>* or <literal>receive_</literal>*
  rules. A rule with the <literal>min_fds</literal> attribute only matches
  messages if they have at least that many Unix file descriptors attached.
  Conversely, a rule with the <literal>max_fds</literal> attribute only
  matches messages if they have no more than that many file descriptors
  attached. In practice, rules with these attributes will most commonly
  take the form
  <literal>&lt;allow send_destination="&hellip;" max_fds="0"/&gt;</literal>,
  <literal>&lt;deny send_destination="&hellip;" min_fds="1"/&gt;</literal> or
  <literal>&lt;deny receive_sender="*" min_fds="1"/&gt;</literal>.
</para>

<para>
  Rules with the <literal>user</literal> or <literal>group</literal>
  attribute are checked when a new connection to the message bus is
  established, and control whether the connection can continue.
  Each of these attributes cannot be combined with any other
  attribute. As a special case, both <literal>user="*"</literal> and
  <literal>group="*"</literal> match any connection. If there are
  no rules of this form, the default is to allow connections from the same
  user ID that owns the <command>dbus-daemon</command> process. The well-known
  session bus normally uses that default behaviour, while the well-known
  system bus normally allows any connection.
</para>

<para>
  Rules with the <literal>own</literal> or <literal>own_prefix</literal>
  attribute are checked when a connection attempts to own a well-known bus
  names. As a special case, <literal>own="*"</literal> matches any well-known
  bus name. The well-known session bus normally allows any connection to
  own any name, while the well-known system bus normally does not allow any
  connection to own any name, except where allowed by further configuration.
  System services that will own a name must install configuration that allows
  them to do so, usually via rules of the form
  <literal>&lt;policy user="some-system-user"&gt;&lt;allow own="&hellip;"/&gt;&lt;/policy&gt;</literal>.
</para>

<para>&lt;allow own_prefix="a.b"/&gt; allows you to own the name "a.b" or any
name whose first dot-separated elements are "a.b": in particular,
you can own "a.b.c" or "a.b.c.d", but not "a.bc" or "a.c".
This is useful when services like Telepathy and ReserveDevice
define a meaning for subtrees of well-known names, such as
org.freedesktop.Telepathy.ConnectionManager.(anything)
and org.freedesktop.ReserveDevice1.(anything).</para>


<para>It does not make sense to deny a user or group inside a &lt;policy&gt;
for a user or group; user/group denials can only be inside
context="default" or context="mandatory" policies.</para>


<para>A single &lt;deny&gt; rule may specify combinations of attributes such as
send_destination and send_interface and send_type. In this case, the
denial applies only if both attributes match the message being denied.
e.g. &lt;deny send_interface="foo.bar" send_destination="foo.blah"/&gt; would
deny messages with the given interface AND the given bus name.
To get an OR effect you specify multiple &lt;deny&gt; rules.</para>


<para>You can't include both send_ and receive_ attributes on the same
rule, since "whether the message can be sent" and "whether it can be
received" are evaluated separately.</para>


<para>Be careful with send_interface/receive_interface, because the
interface field in messages is optional.  In particular, do NOT
specify &lt;deny send_interface="org.foo.Bar"/&gt;!  This will cause
no-interface messages to be blocked for all services, which is
almost certainly not what you intended.  Always use rules of
the form: &lt;deny send_interface="org.foo.Bar" send_destination="org.foo.Service"/&gt;</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;selinux&gt;</emphasis></para></listitem>


</itemizedlist>

<para>The &lt;selinux&gt; element contains settings related to Security Enhanced Linux.
More details below.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;associate&gt;</emphasis></para></listitem>


</itemizedlist>

<para>An &lt;associate&gt; element appears below an &lt;selinux&gt; element and
creates a mapping. Right now only one kind of association is possible:</para>
<literallayout remap='.nf'>
   &lt;associate own="org.freedesktop.Foobar" context="foo_t"/&gt;
</literallayout> <!-- .fi -->


<para>This means that if a connection asks to own the name
"org.freedesktop.Foobar" then the source context will be the context
of the connection and the target context will be "foo_t" - see the
short discussion of SELinux below.</para>


<para>Note, the context here is the target context when requesting a name,
NOT the context of the connection owning the name.</para>


<para>There's currently no way to set a default for owning any name, if
we add this syntax it will look like:</para>
<literallayout remap='.nf'>
   &lt;associate own="*" context="foo_t"/&gt;
</literallayout> <!-- .fi -->
<para>If you find a reason this is useful, let the developers know.
Right now the default will be the security context of the bus itself.</para>


<para>If two &lt;associate&gt; elements specify the same name, the element
appearing later in the configuration file will be used.</para>

<itemizedlist remap='TP'>

  <listitem><para><emphasis remap='I'>&lt;apparmor&gt;</emphasis></para></listitem>


</itemizedlist>

<para>The &lt;apparmor&gt; element is used to configure AppArmor mediation on
the bus. It can contain one attribute that specifies the mediation mode:</para>

<literallayout remap='.nf'>
   &lt;apparmor mode="(enabled|disabled|required)"/&gt;
</literallayout> <!-- .fi -->

<para>The default mode is "enabled". In "enabled" mode, AppArmor mediation
will be performed if AppArmor support is available in the kernel. If it is not
available, dbus-daemon will start but AppArmor mediation will not occur. In
"disabled" mode, AppArmor mediation is disabled. In "required" mode, AppArmor
mediation will be enabled if AppArmor support is available, otherwise
dbus-daemon will refuse to start.</para>

<para>The AppArmor mediation mode of the bus cannot be changed after the bus
starts. Modifying the mode in the configuration file and sending a SIGHUP
signal to the daemon has no effect on the mediation mode.</para>

</refsect1>

<refsect1 id='selinux'><title>SELinux</title>
<para>See <ulink url='http://www.nsa.gov/selinux/'>http://www.nsa.gov/selinux/</ulink> for full details on SELinux. Some useful excerpts:</para>


<para>Every subject (process) and object (e.g. file, socket, IPC object,
etc) in the system is assigned a collection of security attributes,
known as a security context. A security context contains all of the
security attributes associated with a particular subject or object
that are relevant to the security policy.</para>


<para>In order to better encapsulate security contexts and to provide
greater efficiency, the policy enforcement code of SELinux typically
handles security identifiers (SIDs) rather than security contexts. A
SID is an integer that is mapped by the security server to a security
context at runtime.</para>


<para>When a security decision is required, the policy enforcement code
passes a pair of SIDs (typically the SID of a subject and the SID of
an object, but sometimes a pair of subject SIDs or a pair of object
SIDs), and an object security class to the security server. The object
security class indicates the kind of object, e.g. a process, a regular
file, a directory, a TCP socket, etc.</para>


<para>Access decisions specify whether or not a permission is granted for a
given pair of SIDs and class. Each object class has a set of
associated permissions defined to control operations on objects with
that class.</para>


<para>D-Bus performs SELinux security checks in two places.</para>


<para>First, any time a message is routed from one connection to another
connection, the bus daemon will check permissions with the security context of
the first connection as source, security context of the second connection
as target, object class "dbus" and requested permission "send_msg".</para>


<para>If a security context is not available for a connection
(impossible when using UNIX domain sockets), then the target
context used is the context of the bus daemon itself.
There is currently no way to change this default, because we're
assuming that only UNIX domain sockets will be used to
connect to the systemwide bus. If this changes, we'll
probably add a way to set the default connection context.</para>


<para>Second, any time a connection asks to own a name,
the bus daemon will check permissions with the security
context of the connection as source, the security context specified
for the name in the config file as target, object
class "dbus" and requested permission "acquire_svc".</para>


<para>The security context for a bus name is specified with the
&lt;associate&gt; element described earlier in this document.
If a name has no security context associated in the
configuration file, the security context of the bus daemon
itself will be used.</para>

</refsect1>

<refsect1 id='apparmor'><title>AppArmor</title>
<para>The AppArmor confinement context is stored when applications connect to
the bus. The confinement context consists of a label and a confinement mode.
When a security decision is required, the daemon uses the confinement context
to query the AppArmor policy to determine if the action should be allowed or
denied and if the action should be audited.</para>

<para>The daemon performs AppArmor security checks in three places.</para>

<para>First, any time a message is routed from one connection to another
connection, the bus daemon will check permissions with the label of the first
connection as source, label and/or connection name of the second connection as
target, along with the bus name, the path name, the interface name, and the
member name. Reply messages, such as method_return and error messages, are
implicitly allowed if they are in response to a message that has already been
allowed.</para>

<para>Second, any time a connection asks to own a name, the bus daemon will
check permissions with the label of the connection as source, the requested
name as target, along with the bus name.</para>

<para>Third, any time a connection attempts to eavesdrop, the bus daemon will
check permissions with the label of the connection as the source, along with
the bus name.</para>

<para>AppArmor rules for bus mediation are not stored in the bus configuration
files. They are stored in the application's AppArmor profile. Please see
<emphasis remap='I'>apparmor.d(5)</emphasis> for more details.</para>

</refsect1>

<refsect1 id='debugging'><title>DEBUGGING</title>
<para>If you're trying to figure out where your messages are going or why
you aren't getting messages, there are several things you can try.</para>

<para>Remember that the system bus is heavily locked down and if you
haven't installed a security policy file to allow your message
through, it won't work. For the session bus, this is not a concern.</para>

<para>The simplest way to figure out what's happening on the bus is to run
the <emphasis remap='I'>dbus-monitor</emphasis> program, which comes with the D-Bus
package. You can also send test messages with <emphasis remap='I'>dbus-send</emphasis>. These
programs have their own man pages.</para>

<para>If you want to know what the daemon itself is doing, you might consider
running a separate copy of the daemon to test against. This will allow you
to put the daemon under a debugger, or run it with verbose output, without
messing up your real session and system daemons.</para>

<para>To run a separate test copy of the daemon, for example you might open a terminal
and type:</para>
<literallayout remap='.nf'>
  DBUS_VERBOSE=1 dbus-daemon --session --print-address
</literallayout> <!-- .fi -->

<para>The test daemon address will be printed when the daemon starts. You will need
to copy-and-paste this address and use it as the value of the
DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
you want to test. This will cause those applications to connect to your
test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.</para>

<para>DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
was compiled with verbose mode enabled. This is not recommended in
production builds due to performance impact. You may need to rebuild
D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
also affects the D-Bus library and thus applications using D-Bus; it may
be useful to see verbose output on both the client side and from the daemon.)</para>

<para>If you want to get fancy, you can create a custom bus
configuration for your test bus (see the session.conf and system.conf
files that define the two default configurations for example). This
would allow you to specify a different directory for .service files,
for example.</para>

</refsect1>

<refsect1 id='author'><title>AUTHOR</title>
<para>See <ulink url='http://www.freedesktop.org/software/dbus/doc/AUTHORS'>http://www.freedesktop.org/software/dbus/doc/AUTHORS</ulink></para>

</refsect1>

<refsect1 id='bugs'><title>BUGS</title>
<para>Please send bug reports to the D-Bus mailing list or bug tracker,
see <ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink></para>
</refsect1>
</refentry>