1 <?xml version="1.0" encoding="ISO-8859-1"?>
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
3 "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
4 <refentry id='dbusdaemon1'>
6 <!-- dbus\-daemon manual page.
7 Copyright (C) 2003,2008 Red Hat, Inc. -->
10 <refentrytitle>dbus-daemon</refentrytitle>
11 <manvolnum>1</manvolnum>
12 <refmiscinfo class="manual">User Commands</refmiscinfo>
13 <refmiscinfo class="source">D-Bus</refmiscinfo>
14 <refmiscinfo class="version">@DBUS_VERSION@</refmiscinfo>
17 <refname>dbus-daemon</refname>
18 <refpurpose>Message bus daemon</refpurpose>
20 <!-- body begins here -->
21 <refsynopsisdiv id='synopsis'>
23 <command>dbus-daemon</command></cmdsynopsis>
25 <command>dbus-daemon</command> <arg choice='opt'>--version </arg>
26 <arg choice='opt'>--session </arg>
27 <arg choice='opt'>--system </arg>
28 <arg choice='opt'>--config-file=<replaceable>FILE</replaceable></arg>
29 <arg choice='opt'><arg choice='plain'>--print-address </arg><arg choice='opt'><replaceable>=DESCRIPTOR</replaceable></arg></arg>
30 <arg choice='opt'><arg choice='plain'>--print-pid </arg><arg choice='opt'><replaceable>=DESCRIPTOR</replaceable></arg></arg>
31 <arg choice='opt'>--fork </arg>
37 <refsect1 id='description'><title>DESCRIPTION</title>
38 <para><command>dbus-daemon</command> is the D-Bus message bus daemon. See
39 <ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink> for more information about
40 the big picture. D-Bus is first a library that provides one-to-one
41 communication between any two applications; <command>dbus-daemon</command> is an
42 application that uses this library to implement a message bus
43 daemon. Multiple programs connect to the message bus daemon and can
44 exchange messages with one another.</para>
46 <para>There are two standard message bus instances: the systemwide message bus
47 (installed on many systems as the "messagebus" init service) and the
48 per-user-login-session message bus (started each time a user logs in).
49 <command>dbus-daemon</command> is used for both of these instances, but with
50 a different configuration file.</para>
52 <para>The --session option is equivalent to
53 "--config-file=@EXPANDED_DATADIR@/dbus-1/session.conf" and the --system
54 option is equivalent to
55 "--config-file=@EXPANDED_DATADIR@/dbus-1/system.conf". By creating
56 additional configuration files and using the --config-file option,
57 additional special-purpose message bus daemons could be created.</para>
59 <para>The systemwide daemon is normally launched by an init script,
60 standardly called simply "messagebus".</para>
62 <para>The systemwide daemon is largely used for broadcasting system events,
63 such as changes to the printer queue, or adding/removing devices.</para>
65 <para>The per-session daemon is used for various interprocess communication
66 among desktop applications (however, it is not tied to X or the GUI
69 <para>SIGHUP will cause the D-Bus daemon to PARTIALLY reload its
70 configuration file and to flush its user/group information caches. Some
71 configuration changes would require kicking all apps off the bus; so they will
72 only take effect if you restart the daemon. Policy changes should take effect
77 <refsect1 id='options'><title>OPTIONS</title>
78 <para>The following options are supported:</para>
79 <variablelist remap='TP'>
81 <term><option>--config-file=FILE</option></term>
83 <para>Use the given configuration file.</para>
87 <term><option>--fork</option></term>
89 <para>Force the message bus to fork and become a daemon, even if
90 the configuration file does not specify that it should.
91 In most contexts the configuration file already gets this
92 right, though. This option is not supported on Windows.</para>
96 <term><option>--nofork</option></term>
98 <para>Force the message bus not to fork and become a daemon, even if
99 the configuration file specifies that it should. On Windows,
100 the dbus-daemon never forks, so this option is allowed but does
105 <term><option>--print-address[=DESCRIPTOR]</option></term>
107 <para>Print the address of the message bus to standard output, or
108 to the given file descriptor. This is used by programs that
109 launch the message bus.</para>
113 <term><option>--print-pid[=DESCRIPTOR]</option></term>
115 <para>Print the process ID of the message bus to standard output, or
116 to the given file descriptor. This is used by programs that
117 launch the message bus.</para>
121 <term><option>--session</option></term>
123 <para>Use the standard configuration file for the per-login-session message
128 <term><option>--system</option></term>
130 <para>Use the standard configuration file for the systemwide message bus.</para>
134 <term><option>--version</option></term>
136 <para>Print the version of the daemon.</para>
140 <term><option>--introspect</option></term>
142 <para>Print the introspection information for all D-Bus internal interfaces.</para>
146 <term><option>--address[=ADDRESS]</option></term>
148 <para>Set the address to listen on. This option overrides the address
149 configured in the configuration file.</para>
153 <term><option>--systemd-activation</option></term>
155 <para>Enable systemd-style service activation. Only useful in conjunction
156 with the systemd system and session manager on Linux.</para>
160 <term><option>--nopidfile</option></term>
162 <para>Don't write a PID file even if one is configured in the configuration
170 <refsect1 id='configuration_file'><title>CONFIGURATION FILE</title>
171 <para>A message bus daemon has a configuration file that specializes it
172 for a particular application. For example, one configuration
173 file might set up the message bus to be a systemwide message bus,
174 while another might set it up to be a per-user-login-session bus.</para>
176 <para>The configuration file also establishes resource limits, security
177 parameters, and so forth.</para>
179 <para>The configuration file is not part of any interoperability
180 specification and its backward compatibility is not guaranteed; this
181 document is documentation, not specification.</para>
183 <para>The standard systemwide and per-session message bus setups are
184 configured in the files "@EXPANDED_DATADIR@/dbus-1/system.conf" and
185 "@EXPANDED_DATADIR@/dbus-1/session.conf". These files normally
186 <include> a system-local.conf or session-local.conf in
187 @EXPANDED_SYSCONFDIR@/dbus-1; you can put local
188 overrides in those files to avoid modifying the primary configuration
192 <para>The configuration file is an XML document. It must have the following
193 doctype declaration:</para>
194 <literallayout remap='.nf'>
196 <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
197 "<ulink url='http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd'>http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd</ulink>">
199 </literallayout> <!-- .fi -->
202 <para>The following elements may be present in the configuration file.</para>
204 <itemizedlist remap='TP'>
206 <listitem><para><emphasis remap='I'><busconfig></emphasis></para></listitem>
211 <para>Root element.</para>
213 <itemizedlist remap='TP'>
215 <listitem><para><emphasis remap='I'><type></emphasis></para></listitem>
220 <para>The well-known type of the message bus. Currently known values are
221 "system" and "session"; if other values are set, they should be
222 either added to the D-Bus specification, or namespaced. The last
223 <type> element "wins" (previous values are ignored). This element
224 only controls which message bus specific environment variables are
225 set in activated clients. Most of the policy that distinguishes a
226 session bus from the system bus is controlled from the other elements
227 in the configuration file.</para>
230 <para>If the well-known type of the message bus is "session", then the
231 DBUS_STARTER_BUS_TYPE environment variable will be set to "session"
232 and the DBUS_SESSION_BUS_ADDRESS environment variable will be set
233 to the address of the session bus. Likewise, if the type of the
234 message bus is "system", then the DBUS_STARTER_BUS_TYPE environment
235 variable will be set to "system" and the DBUS_SESSION_BUS_ADDRESS
236 environment variable will be set to the address of the system bus
237 (which is normally well known anyway).</para>
240 <para>Example: <type>session</type></para>
242 <itemizedlist remap='TP'>
244 <listitem><para><emphasis remap='I'><include></emphasis></para></listitem>
249 <para>Include a file <include>filename.conf</include> at this point. If the
250 filename is relative, it is located relative to the configuration file
251 doing the including.</para>
254 <para><include> has an optional attribute "ignore_missing=(yes|no)"
255 which defaults to "no" if not provided. This attribute
256 controls whether it's a fatal error for the included file
259 <itemizedlist remap='TP'>
261 <listitem><para><emphasis remap='I'><includedir></emphasis></para></listitem>
266 <para>Include all files in <includedir>foo.d</includedir> at this
267 point. Files in the directory are included in undefined order.
268 Only files ending in ".conf" are included.</para>
271 <para>This is intended to allow extension of the system bus by particular
272 packages. For example, if CUPS wants to be able to send out
273 notification of printer queue changes, it could install a file to
274 @EXPANDED_DATADIR@/dbus-1/system.d or
275 @EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
276 this message and allowed the printer daemon user to send it.</para>
278 <itemizedlist remap='TP'>
280 <listitem><para><emphasis remap='I'><user></emphasis></para></listitem>
285 <para>The user account the daemon should run as, as either a username or a
286 UID. If the daemon cannot change to this UID on startup, it will exit.
287 If this element is not present, the daemon will not change or care
288 about its UID.</para>
291 <para>The last <user> entry in the file "wins", the others are ignored.</para>
294 <para>The user is changed after the bus has completed initialization. So
295 sockets etc. will be created before changing user, but no data will be
296 read from clients before changing user. This means that sockets
297 and PID files can be created in a location that requires root
298 privileges for writing.</para>
300 <itemizedlist remap='TP'>
302 <listitem><para><emphasis remap='I'><fork></emphasis></para></listitem>
307 <para>If present, the bus daemon becomes a real daemon (forks
308 into the background, etc.). This is generally used
309 rather than the --fork command line option.</para>
311 <itemizedlist remap='TP'>
313 <listitem><para><emphasis remap='I'><keep_umask></emphasis></para></listitem>
318 <para>If present, the bus daemon keeps its original umask when forking.
319 This may be useful to avoid affecting the behavior of child processes.</para>
321 <itemizedlist remap='TP'>
323 <listitem><para><emphasis remap='I'><syslog></emphasis></para></listitem>
328 <para>If present, the bus daemon will log to syslog.</para>
330 <itemizedlist remap='TP'>
332 <listitem><para><emphasis remap='I'><pidfile></emphasis></para></listitem>
337 <para>If present, the bus daemon will write its pid to the specified file.
338 The --nopidfile command-line option takes precedence over this setting.</para>
340 <itemizedlist remap='TP'>
342 <listitem><para><emphasis remap='I'><allow_anonymous></emphasis></para></listitem>
347 <para>If present, connections that authenticated using the ANONYMOUS
348 mechanism will be authorized to connect. This option has no practical
349 effect unless the ANONYMOUS mechanism has also been enabled using the
350 <emphasis remap='I'><auth></emphasis> element, described below.</para>
352 <itemizedlist remap='TP'>
354 <listitem><para><emphasis remap='I'><listen></emphasis></para></listitem>
359 <para>Add an address that the bus should listen on. The
360 address is in the standard D-Bus format that contains
361 a transport name plus possible parameters/options.</para>
364 <para>Example: <listen>unix:path=/tmp/foo</listen></para>
367 <para>Example: <listen>tcp:host=localhost,port=1234</listen></para>
370 <para>If there are multiple <listen> elements, then the bus listens
371 on multiple addresses. The bus will pass its address to
372 started services or other interested parties with
373 the last address given in <listen> first. That is,
374 apps will try to connect to the last <listen> address first.</para>
377 <para>tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.
378 If a hostname resolves to multiple addresses, the server will bind
379 to all of them. The family=ipv4 or family=ipv6 options can be used
380 to force it to bind to a subset of addresses</para>
383 <para>Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen></para>
386 <para>A special case is using a port number of zero (or omitting the port),
387 which means to choose an available port selected by the operating
388 system. The port number chosen can be obtained with the
389 --print-address command line parameter and will be present in other
390 cases where the server reports its own address, such as when
391 DBUS_SESSION_BUS_ADDRESS is set.</para>
394 <para>Example: <listen>tcp:host=localhost,port=0</listen></para>
397 <para>tcp/nonce-tcp addresses also allow a bind=hostname option,
398 used in a listenable address to configure the interface on which
399 the server will listen: either the hostname is the IP address of
400 one of the local machine's interfaces (most commonly 127.0.0.1),
401 a DNS name that resolves to one of those IP addresses, '0.0.0.0'
402 to listen on all IPv4 interfaces simultaneously, or '::'
403 to listen on all IPv4 and IPv6 interfaces simultaneously (if supported
404 by the OS). If not specified,
405 the default is the same value as "host".</para>
408 <para>Example: <listen>tcp:host=localhost,bind=0.0.0.0,port=0</listen></para>
410 <itemizedlist remap='TP'>
412 <listitem><para><emphasis remap='I'><auth></emphasis></para></listitem>
417 <para>Lists permitted authorization mechanisms. If this element doesn't
418 exist, then all known mechanisms are allowed. If there are multiple
419 <auth> elements, all the listed mechanisms are allowed. The order in
420 which mechanisms are listed is not meaningful.</para>
423 <para>Example: <auth>EXTERNAL</auth></para>
426 <para>Example: <auth>DBUS_COOKIE_SHA1</auth></para>
428 <itemizedlist remap='TP'>
430 <listitem><para><emphasis remap='I'><servicedir></emphasis></para></listitem>
435 <para>Adds a directory to scan for .service files. Directories are
436 scanned starting with the first to appear in the config file
437 (the first .service file found that provides a particular
438 service will be used).</para>
441 <para>Service files tell the bus how to automatically start a program.
442 They are primarily used with the per-user-session bus,
443 not the systemwide bus.</para>
445 <itemizedlist remap='TP'>
447 <listitem><para><emphasis remap='I'><standard_session_servicedirs/></emphasis></para></listitem>
452 <para><standard_session_servicedirs/> is equivalent to specifying a series
453 of <servicedir/> elements for each of the data directories in the "XDG
454 Base Directory Specification" with the subdirectory "dbus-1/services",
455 so for example "/usr/share/dbus-1/services" would be among the
456 directories searched.</para>
459 <para>The "XDG Base Directory Specification" can be found at
460 <ulink url='http://freedesktop.org/wiki/Standards/basedir-spec'>http://freedesktop.org/wiki/Standards/basedir-spec</ulink> if it hasn't moved,
461 otherwise try your favorite search engine.</para>
464 <para>The <standard_session_servicedirs/> option is only relevant to the
465 per-user-session bus daemon defined in
466 @EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
467 configuration file would probably be nonsense.</para>
469 <itemizedlist remap='TP'>
471 <listitem><para><emphasis remap='I'><standard_system_servicedirs/></emphasis></para></listitem>
476 <para><standard_system_servicedirs/> specifies the standard system-wide
477 activation directories that should be searched for service files.
478 This option defaults to @EXPANDED_DATADIR@/dbus-1/system-services.</para>
481 <para>The <standard_system_servicedirs/> option is only relevant to the
482 per-system bus daemon defined in
483 @EXPANDED_DATADIR@/dbus-1/system.conf. Putting it in any other
484 configuration file would probably be nonsense.</para>
486 <itemizedlist remap='TP'>
488 <listitem><para><emphasis remap='I'><servicehelper/></emphasis></para></listitem>
493 <para><servicehelper/> specifies the setuid helper that is used to launch
494 system daemons with an alternate user. Typically this should be
495 the dbus-daemon-launch-helper executable in located in libexec.</para>
498 <para>The <servicehelper/> option is only relevant to the per-system bus daemon
499 defined in @EXPANDED_DATADIR@/dbus-1/system.conf. Putting it in any other
500 configuration file would probably be nonsense.</para>
502 <itemizedlist remap='TP'>
504 <listitem><para><emphasis remap='I'><limit></emphasis></para></listitem>
509 <para><limit> establishes a resource limit. For example:</para>
510 <literallayout remap='.nf'>
511 <limit name="max_message_size">64</limit>
512 <limit name="max_completed_connections">512</limit>
513 </literallayout> <!-- .fi -->
516 <para>The name attribute is mandatory.
517 Available limit names are:</para>
518 <literallayout remap='.nf'>
519 "max_incoming_bytes" : total size in bytes of messages
520 incoming from a single connection
521 "max_incoming_unix_fds" : total number of unix fds of messages
522 incoming from a single connection
523 "max_outgoing_bytes" : total size in bytes of messages
524 queued up for a single connection
525 "max_outgoing_unix_fds" : total number of unix fds of messages
526 queued up for a single connection
527 "max_message_size" : max size of a single message in
529 "max_message_unix_fds" : max unix fds of a single message
530 "service_start_timeout" : milliseconds (thousandths) until
531 a started service has to connect
532 "auth_timeout" : milliseconds (thousandths) a
533 connection is given to
535 "pending_fd_timeout" : milliseconds (thousandths) a
536 fd is given to be transmitted to
537 dbus-daemon before disconnecting the
539 "max_completed_connections" : max number of authenticated connections
540 "max_incomplete_connections" : max number of unauthenticated
542 "max_connections_per_user" : max number of completed connections from
544 "max_pending_service_starts" : max number of service launches in
545 progress at the same time
546 "max_names_per_connection" : max number of names a single
548 "max_match_rules_per_connection": max number of match rules for a single
550 "max_replies_per_connection" : max number of pending method
551 replies per connection
552 (number of calls-in-progress)
553 "reply_timeout" : milliseconds (thousandths)
554 until a method call times out
555 </literallayout> <!-- .fi -->
558 <para>The max incoming/outgoing queue sizes allow a new message to be queued
559 if one byte remains below the max. So you can in fact exceed the max
560 by max_message_size.</para>
563 <para>max_completed_connections divided by max_connections_per_user is the
564 number of users that can work together to denial-of-service all other users by using
565 up all connections on the systemwide bus.</para>
568 <para>Limits are normally only of interest on the systemwide bus, not the user session
571 <itemizedlist remap='TP'>
573 <listitem><para><emphasis remap='I'><policy></emphasis></para></listitem>
578 <para>The <policy> element defines a security policy to be applied to a particular
579 set of connections to the bus. A policy is made up of
580 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
581 they are analogous to a firewall in that they allow expected traffic
582 and prevent unexpected traffic.</para>
585 <para>Currently, the system bus has a default-deny policy for sending method calls
586 and owning bus names. Everything else, in particular reply messages, receive
587 checks, and signals has a default allow policy.</para>
590 <para>In general, it is best to keep system services as small, targeted programs which
591 run in their own process and provide a single bus name. Then, all that is needed
592 is an <allow> rule for the "own" permission to let the process claim the bus
593 name, and a "send_destination" rule to allow traffic from some or all uids to
597 <para>The <policy> element has one of four attributes:</para>
598 <literallayout remap='.nf'>
599 context="(default|mandatory)"
600 at_console="(true|false)"
601 user="username or userid"
602 group="group name or gid"
603 </literallayout> <!-- .fi -->
606 <para>Policies are applied to a connection as follows:</para>
607 <literallayout remap='.nf'>
608 - all context="default" policies are applied
609 - all group="connection's user's group" policies are applied
611 - all user="connection's auth user" policies are applied
613 - all at_console="true" policies are applied
614 - all at_console="false" policies are applied
615 - all context="mandatory" policies are applied
616 </literallayout> <!-- .fi -->
619 <para>Policies applied later will override those applied earlier,
620 when the policies overlap. Multiple policies with the same
621 user/group/context are applied in the order they appear
622 in the config file.</para>
624 <variablelist remap='TP'>
626 <term><emphasis remap='I'><deny></emphasis></term>
628 <para><emphasis remap='I'><allow></emphasis></para>
634 <para>A <deny> element appears below a <policy> element and prohibits some
635 action. The <allow> element makes an exception to previous <deny>
636 statements, and works just like <deny> but with the inverse meaning.</para>
639 <para>The possible attributes of these elements are:</para>
640 <literallayout remap='.nf'>
641 send_interface="interface_name"
642 send_member="method_or_signal_name"
643 send_error="error_name"
644 send_destination="name"
645 send_type="method_call" | "method_return" | "signal" | "error"
646 send_path="/path/name"
648 receive_interface="interface_name"
649 receive_member="method_or_signal_name"
650 receive_error="error_name"
651 receive_sender="name"
652 receive_type="method_call" | "method_return" | "signal" | "error"
653 receive_path="/path/name"
655 send_requested_reply="true" | "false"
656 receive_requested_reply="true" | "false"
658 eavesdrop="true" | "false"
664 </literallayout> <!-- .fi -->
667 <para>Examples:</para>
668 <literallayout remap='.nf'>
669 <deny send_destination="org.freedesktop.Service" send_interface="org.freedesktop.System" send_member="Reboot"/>
670 <deny send_destination="org.freedesktop.System"/>
671 <deny receive_sender="org.freedesktop.System"/>
672 <deny user="john"/>
673 <deny group="enemies"/>
674 </literallayout> <!-- .fi -->
677 <para>The <deny> element's attributes determine whether the deny "matches" a
678 particular action. If it matches, the action is denied (unless later
679 rules in the config file allow it).</para>
681 <para>send_destination and receive_sender rules mean that messages may not be
682 sent to or received from the *owner* of the given name, not that
683 they may not be sent *to that name*. That is, if a connection
684 owns services A, B, C, and sending to A is denied, sending to B or C
685 will not work either.</para>
687 <para>The other send_* and receive_* attributes are purely textual/by-value
688 matches against the given field in the message header.</para>
690 <para>"Eavesdropping" occurs when an application receives a message that
691 was explicitly addressed to a name the application does not own, or
692 is a reply to such a message. Eavesdropping thus only applies to
693 messages that are addressed to services and replies to such messages
694 (i.e. it does not apply to signals).</para>
696 <para>For <allow>, eavesdrop="true" indicates that the rule matches even
697 when eavesdropping. eavesdrop="false" is the default and means that
698 the rule only allows messages to go to their specified recipient.
699 For <deny>, eavesdrop="true" indicates that the rule matches
700 only when eavesdropping. eavesdrop="false" is the default for <deny>
701 also, but here it means that the rule applies always, even when
702 not eavesdropping. The eavesdrop attribute can only be combined with
703 send and receive rules (with send_* and receive_* attributes).</para>
705 <para>The [send|receive]_requested_reply attribute works similarly to the eavesdrop
706 attribute. It controls whether the <deny> or <allow> matches a reply
707 that is expected (corresponds to a previous method call message).
708 This attribute only makes sense for reply messages (errors and method
709 returns), and is ignored for other message types.</para>
712 <para>For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
713 only requested replies are allowed by the
714 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
715 even if unexpected.</para>
718 <para>For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
719 the rule matches only when the reply was not
720 requested. [send|receive]_requested_reply="true" indicates that the rule applies
721 always, regardless of pending reply state.</para>
724 <para>user and group denials mean that the given user or group may
725 not connect to the message bus.</para>
728 <para>For "name", "username", "groupname", etc.
729 the character "*" can be substituted, meaning "any." Complex globs
730 like "foo.bar.*" aren't allowed for now because they'd be work to
731 implement and maybe encourage sloppy security anyway.</para>
734 <para><allow own_prefix="a.b"/> allows you to own the name "a.b" or any
735 name whose first dot-separated elements are "a.b": in particular,
736 you can own "a.b.c" or "a.b.c.d", but not "a.bc" or "a.c".
737 This is useful when services like Telepathy and ReserveDevice
738 define a meaning for subtrees of well-known names, such as
739 org.freedesktop.Telepathy.ConnectionManager.(anything)
740 and org.freedesktop.ReserveDevice1.(anything).</para>
743 <para>It does not make sense to deny a user or group inside a <policy>
744 for a user or group; user/group denials can only be inside
745 context="default" or context="mandatory" policies.</para>
748 <para>A single <deny> rule may specify combinations of attributes such as
749 send_destination and send_interface and send_type. In this case, the
750 denial applies only if both attributes match the message being denied.
751 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
752 deny messages with the given interface AND the given bus name.
753 To get an OR effect you specify multiple <deny> rules.</para>
756 <para>You can't include both send_ and receive_ attributes on the same
757 rule, since "whether the message can be sent" and "whether it can be
758 received" are evaluated separately.</para>
761 <para>Be careful with send_interface/receive_interface, because the
762 interface field in messages is optional. In particular, do NOT
763 specify <deny send_interface="org.foo.Bar"/>! This will cause
764 no-interface messages to be blocked for all services, which is
765 almost certainly not what you intended. Always use rules of
766 the form: <deny send_interface="org.foo.Bar" send_destination="org.foo.Service"/></para>
768 <itemizedlist remap='TP'>
770 <listitem><para><emphasis remap='I'><selinux></emphasis></para></listitem>
775 <para>The <selinux> element contains settings related to Security Enhanced Linux.
776 More details below.</para>
778 <itemizedlist remap='TP'>
780 <listitem><para><emphasis remap='I'><associate></emphasis></para></listitem>
785 <para>An <associate> element appears below an <selinux> element and
786 creates a mapping. Right now only one kind of association is possible:</para>
787 <literallayout remap='.nf'>
788 <associate own="org.freedesktop.Foobar" context="foo_t"/>
789 </literallayout> <!-- .fi -->
792 <para>This means that if a connection asks to own the name
793 "org.freedesktop.Foobar" then the source context will be the context
794 of the connection and the target context will be "foo_t" - see the
795 short discussion of SELinux below.</para>
798 <para>Note, the context here is the target context when requesting a name,
799 NOT the context of the connection owning the name.</para>
802 <para>There's currently no way to set a default for owning any name, if
803 we add this syntax it will look like:</para>
804 <literallayout remap='.nf'>
805 <associate own="*" context="foo_t"/>
806 </literallayout> <!-- .fi -->
807 <para>If you find a reason this is useful, let the developers know.
808 Right now the default will be the security context of the bus itself.</para>
811 <para>If two <associate> elements specify the same name, the element
812 appearing later in the configuration file will be used.</para>
814 <itemizedlist remap='TP'>
816 <listitem><para><emphasis remap='I'><apparmor></emphasis></para></listitem>
821 <para>The <apparmor> element is used to configure AppArmor mediation on
822 the bus. It can contain one attribute that specifies the mediation mode:</para>
824 <literallayout remap='.nf'>
825 <apparmor mode="(enabled|disabled|required)"/>
826 </literallayout> <!-- .fi -->
828 <para>The default mode is "enabled". In "enabled" mode, AppArmor mediation
829 will be performed if AppArmor support is available in the kernel. If it is not
830 available, dbus-daemon will start but AppArmor mediation will not occur. In
831 "disabled" mode, AppArmor mediation is disabled. In "required" mode, AppArmor
832 mediation will be enabled if AppArmor support is available, otherwise
833 dbus-daemon will refuse to start.</para>
835 <para>The AppArmor mediation mode of the bus cannot be changed after the bus
836 starts. Modifying the mode in the configuration file and sending a SIGHUP
837 signal to the daemon has no effect on the mediation mode.</para>
841 <refsect1 id='selinux'><title>SELinux</title>
842 <para>See <ulink url='http://www.nsa.gov/selinux/'>http://www.nsa.gov/selinux/</ulink> for full details on SELinux. Some useful excerpts:</para>
845 <para>Every subject (process) and object (e.g. file, socket, IPC object,
846 etc) in the system is assigned a collection of security attributes,
847 known as a security context. A security context contains all of the
848 security attributes associated with a particular subject or object
849 that are relevant to the security policy.</para>
852 <para>In order to better encapsulate security contexts and to provide
853 greater efficiency, the policy enforcement code of SELinux typically
854 handles security identifiers (SIDs) rather than security contexts. A
855 SID is an integer that is mapped by the security server to a security
856 context at runtime.</para>
859 <para>When a security decision is required, the policy enforcement code
860 passes a pair of SIDs (typically the SID of a subject and the SID of
861 an object, but sometimes a pair of subject SIDs or a pair of object
862 SIDs), and an object security class to the security server. The object
863 security class indicates the kind of object, e.g. a process, a regular
864 file, a directory, a TCP socket, etc.</para>
867 <para>Access decisions specify whether or not a permission is granted for a
868 given pair of SIDs and class. Each object class has a set of
869 associated permissions defined to control operations on objects with
873 <para>D-Bus performs SELinux security checks in two places.</para>
876 <para>First, any time a message is routed from one connection to another
877 connection, the bus daemon will check permissions with the security context of
878 the first connection as source, security context of the second connection
879 as target, object class "dbus" and requested permission "send_msg".</para>
882 <para>If a security context is not available for a connection
883 (impossible when using UNIX domain sockets), then the target
884 context used is the context of the bus daemon itself.
885 There is currently no way to change this default, because we're
886 assuming that only UNIX domain sockets will be used to
887 connect to the systemwide bus. If this changes, we'll
888 probably add a way to set the default connection context.</para>
891 <para>Second, any time a connection asks to own a name,
892 the bus daemon will check permissions with the security
893 context of the connection as source, the security context specified
894 for the name in the config file as target, object
895 class "dbus" and requested permission "acquire_svc".</para>
898 <para>The security context for a bus name is specified with the
899 <associate> element described earlier in this document.
900 If a name has no security context associated in the
901 configuration file, the security context of the bus daemon
902 itself will be used.</para>
906 <refsect1 id='apparmor'><title>AppArmor</title>
907 <para>The AppArmor confinement context is stored when applications connect to
908 the bus. The confinement context consists of a label and a confinement mode.
909 When a security decision is required, the daemon uses the confinement context
910 to query the AppArmor policy to determine if the action should be allowed or
911 denied and if the action should be audited.</para>
913 <para>The daemon performs AppArmor security checks in three places.</para>
915 <para>First, any time a message is routed from one connection to another
916 connection, the bus daemon will check permissions with the label of the first
917 connection as source, label and/or connection name of the second connection as
918 target, along with the bus name, the path name, the interface name, and the
919 member name. Reply messages, such as method_return and error messages, are
920 implicitly allowed if they are in response to a message that has already been
923 <para>Second, any time a connection asks to own a name, the bus daemon will
924 check permissions with the label of the connection as source, the requested
925 name as target, along with the bus name.</para>
927 <para>Third, any time a connection attempts to eavesdrop, the bus daemon will
928 check permissions with the label of the connection as the source, along with
931 <para>AppArmor rules for bus mediation are not stored in the bus configuration
932 files. They are stored in the application's AppArmor profile. Please see
933 <emphasis remap='I'>apparmor.d(5)</emphasis> for more details.</para>
937 <refsect1 id='debugging'><title>DEBUGGING</title>
938 <para>If you're trying to figure out where your messages are going or why
939 you aren't getting messages, there are several things you can try.</para>
941 <para>Remember that the system bus is heavily locked down and if you
942 haven't installed a security policy file to allow your message
943 through, it won't work. For the session bus, this is not a concern.</para>
945 <para>The simplest way to figure out what's happening on the bus is to run
946 the <emphasis remap='I'>dbus-monitor</emphasis> program, which comes with the D-Bus
947 package. You can also send test messages with <emphasis remap='I'>dbus-send</emphasis>. These
948 programs have their own man pages.</para>
950 <para>If you want to know what the daemon itself is doing, you might consider
951 running a separate copy of the daemon to test against. This will allow you
952 to put the daemon under a debugger, or run it with verbose output, without
953 messing up your real session and system daemons.</para>
955 <para>To run a separate test copy of the daemon, for example you might open a terminal
957 <literallayout remap='.nf'>
958 DBUS_VERBOSE=1 dbus-daemon --session --print-address
959 </literallayout> <!-- .fi -->
961 <para>The test daemon address will be printed when the daemon starts. You will need
962 to copy-and-paste this address and use it as the value of the
963 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
964 you want to test. This will cause those applications to connect to your
965 test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.</para>
967 <para>DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
968 was compiled with verbose mode enabled. This is not recommended in
969 production builds due to performance impact. You may need to rebuild
970 D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
971 also affects the D-Bus library and thus applications using D-Bus; it may
972 be useful to see verbose output on both the client side and from the daemon.)</para>
974 <para>If you want to get fancy, you can create a custom bus
975 configuration for your test bus (see the session.conf and system.conf
976 files that define the two default configurations for example). This
977 would allow you to specify a different directory for .service files,
982 <refsect1 id='author'><title>AUTHOR</title>
983 <para>See <ulink url='http://www.freedesktop.org/software/dbus/doc/AUTHORS'>http://www.freedesktop.org/software/dbus/doc/AUTHORS</ulink></para>
987 <refsect1 id='bugs'><title>BUGS</title>
988 <para>Please send bug reports to the D-Bus mailing list or bug tracker,
989 see <ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink></para>