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2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
3 "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
4 <!-- lifted from troff+man by doclifter -->
5 <refentry id='dbusdaemon1in'>
7 <!-- dbus\-daemon manual page.
8 Copyright (C) 2003,2008 Red Hat, Inc. -->
11 <refentrytitle>dbus-daemon</refentrytitle>
12 <manvolnum>1</manvolnum>
15 <refname>dbus-daemon</refname>
16 <refpurpose>Message bus daemon</refpurpose>
18 <!-- body begins here -->
19 <refsynopsisdiv id='synopsis'>
21 <command>dbus-daemon</command></cmdsynopsis>
23 <command>dbus-daemon</command> <arg choice='opt'>--version </arg>
24 <arg choice='opt'>--session </arg>
25 <arg choice='opt'>--system </arg>
26 <arg choice='opt'>--config-file=<replaceable>FILE</replaceable></arg>
27 <arg choice='opt'><arg choice='plain'>--print-address </arg><arg choice='opt'><replaceable>=DESCRIPTOR</replaceable></arg></arg>
28 <arg choice='opt'><arg choice='plain'>--print-pid </arg><arg choice='opt'><replaceable>=DESCRIPTOR</replaceable></arg></arg>
29 <arg choice='opt'>--fork </arg>
35 <refsect1 id='description'><title>DESCRIPTION</title>
36 <para><command>dbus-daemon</command> is the D-Bus message bus daemon. See
37 <ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink> for more information about
38 the big picture. D-Bus is first a library that provides one-to-one
39 communication between any two applications; <command>dbus-daemon</command> is an
40 application that uses this library to implement a message bus
41 daemon. Multiple programs connect to the message bus daemon and can
42 exchange messages with one another.</para>
44 <para>There are two standard message bus instances: the systemwide message bus
45 (installed on many systems as the "messagebus" init service) and the
46 per-user-login-session message bus (started each time a user logs in).
47 <command>dbus-daemon</command> is used for both of these instances, but with
48 a different configuration file.</para>
50 <para>The --session option is equivalent to
51 "--config-file=@EXPANDED_SYSCONFDIR@/dbus-1/session.conf" and the --system
52 option is equivalent to
53 "--config-file=@EXPANDED_SYSCONFDIR@/dbus-1/system.conf". By creating
54 additional configuration files and using the --config-file option,
55 additional special-purpose message bus daemons could be created.</para>
57 <para>The systemwide daemon is normally launched by an init script,
58 standardly called simply "messagebus".</para>
60 <para>The systemwide daemon is largely used for broadcasting system events,
61 such as changes to the printer queue, or adding/removing devices.</para>
63 <para>The per-session daemon is used for various interprocess communication
64 among desktop applications (however, it is not tied to X or the GUI
67 <para>SIGHUP will cause the D-Bus daemon to PARTIALLY reload its
68 configuration file and to flush its user/group information caches. Some
69 configuration changes would require kicking all apps off the bus; so they will
70 only take effect if you restart the daemon. Policy changes should take effect
75 <refsect1 id='options'><title>OPTIONS</title>
76 <para>The following options are supported:</para>
77 <variablelist remap='TP'>
79 <term><option>--config-file=FILE</option></term>
81 <para>Use the given configuration file.</para>
85 <term><option>--fork</option></term>
87 <para>Force the message bus to fork and become a daemon, even if
88 the configuration file does not specify that it should.
89 In most contexts the configuration file already gets this
91 <option>--nofork</option>
92 Force the message bus not to fork and become a daemon, even if
93 the configuration file specifies that it should.</para>
97 <term><option>--print-address[=DESCRIPTOR]</option></term>
99 <para>Print the address of the message bus to standard output, or
100 to the given file descriptor. This is used by programs that
101 launch the message bus.</para>
105 <term><option>--print-pid[=DESCRIPTOR]</option></term>
107 <para>Print the process ID 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>--session</option></term>
115 <para>Use the standard configuration file for the per-login-session message
120 <term><option>--system</option></term>
122 <para>Use the standard configuration file for the systemwide message bus.</para>
126 <term><option>--version</option></term>
128 <para>Print the version of the daemon.</para>
132 <term><option>--introspect</option></term>
134 <para>Print the introspection information for all D-Bus internal interfaces.</para>
138 <term><option>--address[=ADDRESS]</option></term>
140 <para>Set the address to listen on. This option overrides the address
141 configured in the configuration file.</para>
145 <term><option>--systemd-activation</option></term>
147 <para>Enable systemd-style service activation. Only useful in conjunction
148 with the systemd system and session manager on Linux.</para>
152 <term><option>--nopidfile</option></term>
154 <para>Don't write a PID file even if one is configured in the configuration
162 <refsect1 id='configuration_file'><title>CONFIGURATION FILE</title>
163 <para>A message bus daemon has a configuration file that specializes it
164 for a particular application. For example, one configuration
165 file might set up the message bus to be a systemwide message bus,
166 while another might set it up to be a per-user-login-session bus.</para>
168 <para>The configuration file also establishes resource limits, security
169 parameters, and so forth.</para>
171 <para>The configuration file is not part of any interoperability
172 specification and its backward compatibility is not guaranteed; this
173 document is documentation, not specification.</para>
175 <para>The standard systemwide and per-session message bus setups are
176 configured in the files "@EXPANDED_SYSCONFDIR@/dbus-1/system.conf" and
177 "@EXPANDED_SYSCONFDIR@/dbus-1/session.conf". These files normally
178 <include> a system-local.conf or session-local.conf; you can put local
179 overrides in those files to avoid modifying the primary configuration
183 <para>The configuration file is an XML document. It must have the following
184 doctype declaration:</para>
185 <literallayout remap='.nf'>
187 <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
188 "<ulink url='http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd'>http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd</ulink>">
190 </literallayout> <!-- .fi -->
193 <para>The following elements may be present in the configuration file.</para>
195 <itemizedlist remap='TP'>
197 <listitem><para><emphasis remap='I'><busconfig></emphasis></para></listitem>
202 <para>Root element.</para>
204 <itemizedlist remap='TP'>
206 <listitem><para><emphasis remap='I'><type></emphasis></para></listitem>
211 <para>The well-known type of the message bus. Currently known values are
212 "system" and "session"; if other values are set, they should be
213 either added to the D-Bus specification, or namespaced. The last
214 <type> element "wins" (previous values are ignored). This element
215 only controls which message bus specific environment variables are
216 set in activated clients. Most of the policy that distinguishes a
217 session bus from the system bus is controlled from the other elements
218 in the configuration file.</para>
221 <para>If the well-known type of the message bus is "session", then the
222 DBUS_STARTER_BUS_TYPE environment variable will be set to "session"
223 and the DBUS_SESSION_BUS_ADDRESS environment variable will be set
224 to the address of the session bus. Likewise, if the type of the
225 message bus is "system", then the DBUS_STARTER_BUS_TYPE environment
226 variable will be set to "system" and the DBUS_SESSION_BUS_ADDRESS
227 environment variable will be set to the address of the system bus
228 (which is normally well known anyway).</para>
231 <para>Example: <type>session</type></para>
233 <itemizedlist remap='TP'>
235 <listitem><para><emphasis remap='I'><include></emphasis></para></listitem>
240 <para>Include a file <include>filename.conf</include> at this point. If the
241 filename is relative, it is located relative to the configuration file
242 doing the including.</para>
245 <para><include> has an optional attribute "ignore_missing=(yes|no)"
246 which defaults to "no" if not provided. This attribute
247 controls whether it's a fatal error for the included file
250 <itemizedlist remap='TP'>
252 <listitem><para><emphasis remap='I'><includedir></emphasis></para></listitem>
257 <para>Include all files in <includedir>foo.d</includedir> at this
258 point. Files in the directory are included in undefined order.
259 Only files ending in ".conf" are included.</para>
262 <para>This is intended to allow extension of the system bus by particular
263 packages. For example, if CUPS wants to be able to send out
264 notification of printer queue changes, it could install a file to
265 @EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
266 this message and allowed the printer daemon user to send it.</para>
268 <itemizedlist remap='TP'>
270 <listitem><para><emphasis remap='I'><user></emphasis></para></listitem>
275 <para>The user account the daemon should run as, as either a username or a
276 UID. If the daemon cannot change to this UID on startup, it will exit.
277 If this element is not present, the daemon will not change or care
278 about its UID.</para>
281 <para>The last <user> entry in the file "wins", the others are ignored.</para>
284 <para>The user is changed after the bus has completed initialization. So
285 sockets etc. will be created before changing user, but no data will be
286 read from clients before changing user. This means that sockets
287 and PID files can be created in a location that requires root
288 privileges for writing.</para>
290 <itemizedlist remap='TP'>
292 <listitem><para><emphasis remap='I'><fork></emphasis></para></listitem>
297 <para>If present, the bus daemon becomes a real daemon (forks
298 into the background, etc.). This is generally used
299 rather than the --fork command line option.</para>
301 <itemizedlist remap='TP'>
303 <listitem><para><emphasis remap='I'><keep_umask></emphasis></para></listitem>
308 <para>If present, the bus daemon keeps its original umask when forking.
309 This may be useful to avoid affecting the behavior of child processes.</para>
311 <itemizedlist remap='TP'>
313 <listitem><para><emphasis remap='I'><listen></emphasis></para></listitem>
318 <para>Add an address that the bus should listen on. The
319 address is in the standard D-Bus format that contains
320 a transport name plus possible parameters/options.</para>
323 <para>Example: <listen>unix:path=/tmp/foo</listen></para>
326 <para>Example: <listen>tcp:host=localhost,port=1234</listen></para>
329 <para>If there are multiple <listen> elements, then the bus listens
330 on multiple addresses. The bus will pass its address to
331 started services or other interested parties with
332 the last address given in <listen> first. That is,
333 apps will try to connect to the last <listen> address first.</para>
336 <para>tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.
337 If a hostname resolves to multiple addresses, the server will bind
338 to all of them. The family=ipv4 or family=ipv6 options can be used
339 to force it to bind to a subset of addresses</para>
342 <para>Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen></para>
345 <para>A special case is using a port number of zero (or omitting the port),
346 which means to choose an available port selected by the operating
347 system. The port number chosen can be obtained with the
348 --print-address command line parameter and will be present in other
349 cases where the server reports its own address, such as when
350 DBUS_SESSION_BUS_ADDRESS is set.</para>
353 <para>Example: <listen>tcp:host=localhost,port=0</listen></para>
356 <para>tcp addresses also allow a bind=hostname option, which will override
357 the host option specifying what address to bind to, without changing
358 the address reported by the bus. The bind option can also take a
359 special name '*' to cause the bus to listen on all local address
360 (INADDR_ANY). The specified host should be a valid name of the local
361 machine or weird stuff will happen.</para>
364 <para>Example: <listen>tcp:host=localhost,bind=*,port=0</listen></para>
366 <itemizedlist remap='TP'>
368 <listitem><para><emphasis remap='I'><auth></emphasis></para></listitem>
373 <para>Lists permitted authorization mechanisms. If this element doesn't
374 exist, then all known mechanisms are allowed. If there are multiple
375 <auth> elements, all the listed mechanisms are allowed. The order in
376 which mechanisms are listed is not meaningful.</para>
379 <para>Example: <auth>EXTERNAL</auth></para>
382 <para>Example: <auth>DBUS_COOKIE_SHA1</auth></para>
384 <itemizedlist remap='TP'>
386 <listitem><para><emphasis remap='I'><servicedir></emphasis></para></listitem>
391 <para>Adds a directory to scan for .service files. Directories are
392 scanned starting with the last to appear in the config file
393 (the first .service file found that provides a particular
394 service will be used).</para>
397 <para>Service files tell the bus how to automatically start a program.
398 They are primarily used with the per-user-session bus,
399 not the systemwide bus.</para>
401 <itemizedlist remap='TP'>
403 <listitem><para><emphasis remap='I'><standard_session_servicedirs/></emphasis></para></listitem>
408 <para><standard_session_servicedirs/> is equivalent to specifying a series
409 of <servicedir/> elements for each of the data directories in the "XDG
410 Base Directory Specification" with the subdirectory "dbus-1/services",
411 so for example "/usr/share/dbus-1/services" would be among the
412 directories searched.</para>
415 <para>The "XDG Base Directory Specification" can be found at
416 <ulink url='http://freedesktop.org/wiki/Standards/basedir-spec'>http://freedesktop.org/wiki/Standards/basedir-spec</ulink> if it hasn't moved,
417 otherwise try your favorite search engine.</para>
420 <para>The <standard_session_servicedirs/> option is only relevant to the
421 per-user-session bus daemon defined in
422 @EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
423 configuration file would probably be nonsense.</para>
425 <itemizedlist remap='TP'>
427 <listitem><para><emphasis remap='I'><standard_system_servicedirs/></emphasis></para></listitem>
432 <para><standard_system_servicedirs/> specifies the standard system-wide
433 activation directories that should be searched for service files.
434 This option defaults to @EXPANDED_DATADIR@/dbus-1/system-services.</para>
437 <para>The <standard_system_servicedirs/> option is only relevant to the
438 per-system bus daemon defined in
439 @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
440 configuration file would probably be nonsense.</para>
442 <itemizedlist remap='TP'>
444 <listitem><para><emphasis remap='I'><servicehelper/></emphasis></para></listitem>
449 <para><servicehelper/> specifies the setuid helper that is used to launch
450 system daemons with an alternate user. Typically this should be
451 the dbus-daemon-launch-helper executable in located in libexec.</para>
454 <para>The <servicehelper/> option is only relevant to the per-system bus daemon
455 defined in @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
456 configuration file would probably be nonsense.</para>
458 <itemizedlist remap='TP'>
460 <listitem><para><emphasis remap='I'><limit></emphasis></para></listitem>
465 <para><limit> establishes a resource limit. For example:</para>
466 <literallayout remap='.nf'>
467 <limit name="max_message_size">64</limit>
468 <limit name="max_completed_connections">512</limit>
469 </literallayout> <!-- .fi -->
472 <para>The name attribute is mandatory.
473 Available limit names are:</para>
474 <literallayout remap='.nf'>
475 "max_incoming_bytes" : total size in bytes of messages
476 incoming from a single connection
477 "max_incoming_unix_fds" : total number of unix fds of messages
478 incoming from a single connection
479 "max_outgoing_bytes" : total size in bytes of messages
480 queued up for a single connection
481 "max_outgoing_unix_fds" : total number of unix fds of messages
482 queued up for a single connection
483 "max_message_size" : max size of a single message in
485 "max_message_unix_fds" : max unix fds of a single message
486 "service_start_timeout" : milliseconds (thousandths) until
487 a started service has to connect
488 "auth_timeout" : milliseconds (thousandths) a
489 connection is given to
491 "max_completed_connections" : max number of authenticated connections
492 "max_incomplete_connections" : max number of unauthenticated
494 "max_connections_per_user" : max number of completed connections from
496 "max_pending_service_starts" : max number of service launches in
497 progress at the same time
498 "max_names_per_connection" : max number of names a single
500 "max_match_rules_per_connection": max number of match rules for a single
502 "max_replies_per_connection" : max number of pending method
503 replies per connection
504 (number of calls-in-progress)
505 "reply_timeout" : milliseconds (thousandths)
506 until a method call times out
507 </literallayout> <!-- .fi -->
510 <para>The max incoming/outgoing queue sizes allow a new message to be queued
511 if one byte remains below the max. So you can in fact exceed the max
512 by max_message_size.</para>
515 <para>max_completed_connections divided by max_connections_per_user is the
516 number of users that can work together to denial-of-service all other users by using
517 up all connections on the systemwide bus.</para>
520 <para>Limits are normally only of interest on the systemwide bus, not the user session
523 <itemizedlist remap='TP'>
525 <listitem><para><emphasis remap='I'><policy></emphasis></para></listitem>
530 <para>The <policy> element defines a security policy to be applied to a particular
531 set of connections to the bus. A policy is made up of
532 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
533 they are analogous to a firewall in that they allow expected traffic
534 and prevent unexpected traffic.</para>
537 <para>Currently, the system bus has a default-deny policy for sending method calls
538 and owning bus names. Everything else, in particular reply messages, receive
539 checks, and signals has a default allow policy.</para>
542 <para>In general, it is best to keep system services as small, targeted programs which
543 run in their own process and provide a single bus name. Then, all that is needed
544 is an <allow> rule for the "own" permission to let the process claim the bus
545 name, and a "send_destination" rule to allow traffic from some or all uids to
549 <para>The <policy> element has one of four attributes:</para>
550 <literallayout remap='.nf'>
551 context="(default|mandatory)"
552 at_console="(true|false)"
553 user="username or userid"
554 group="group name or gid"
555 </literallayout> <!-- .fi -->
558 <para>Policies are applied to a connection as follows:</para>
559 <literallayout remap='.nf'>
560 - all context="default" policies are applied
561 - all group="connection's user's group" policies are applied
563 - all user="connection's auth user" policies are applied
565 - all at_console="true" policies are applied
566 - all at_console="false" policies are applied
567 - all context="mandatory" policies are applied
568 </literallayout> <!-- .fi -->
571 <para>Policies applied later will override those applied earlier,
572 when the policies overlap. Multiple policies with the same
573 user/group/context are applied in the order they appear
574 in the config file.</para>
576 <variablelist remap='TP'>
578 <term><emphasis remap='I'><deny></emphasis></term>
580 <para><emphasis remap='I'><allow></emphasis></para>
586 <para>A <deny> element appears below a <policy> element and prohibits some
587 action. The <allow> element makes an exception to previous <deny>
588 statements, and works just like <deny> but with the inverse meaning.</para>
591 <para>The possible attributes of these elements are:</para>
592 <literallayout remap='.nf'>
593 send_interface="interface_name"
594 send_member="method_or_signal_name"
595 send_error="error_name"
596 send_destination="name"
597 send_type="method_call" | "method_return" | "signal" | "error"
598 send_path="/path/name"
600 receive_interface="interface_name"
601 receive_member="method_or_signal_name"
602 receive_error="error_name"
603 receive_sender="name"
604 receive_type="method_call" | "method_return" | "signal" | "error"
605 receive_path="/path/name"
607 send_requested_reply="true" | "false"
608 receive_requested_reply="true" | "false"
610 eavesdrop="true" | "false"
616 </literallayout> <!-- .fi -->
619 <para>Examples:</para>
620 <literallayout remap='.nf'>
621 <deny send_destination="org.freedesktop.Service" send_interface="org.freedesktop.System" send_member="Reboot"/>
622 <deny send_destination="org.freedesktop.System"/>
623 <deny receive_sender="org.freedesktop.System"/>
624 <deny user="john"/>
625 <deny group="enemies"/>
626 </literallayout> <!-- .fi -->
629 <para>The <deny> element's attributes determine whether the deny "matches" a
630 particular action. If it matches, the action is denied (unless later
631 rules in the config file allow it).</para>
633 <para>send_destination and receive_sender rules mean that messages may not be
634 sent to or received from the *owner* of the given name, not that
635 they may not be sent *to that name*. That is, if a connection
636 owns services A, B, C, and sending to A is denied, sending to B or C
637 will not work either.</para>
639 <para>The other send_* and receive_* attributes are purely textual/by-value
640 matches against the given field in the message header.</para>
642 <para>"Eavesdropping" occurs when an application receives a message that
643 was explicitly addressed to a name the application does not own, or
644 is a reply to such a message. Eavesdropping thus only applies to
645 messages that are addressed to services and replies to such messages
646 (i.e. it does not apply to signals).</para>
648 <para>For <allow>, eavesdrop="true" indicates that the rule matches even
649 when eavesdropping. eavesdrop="false" is the default and means that
650 the rule only allows messages to go to their specified recipient.
651 For <deny>, eavesdrop="true" indicates that the rule matches
652 only when eavesdropping. eavesdrop="false" is the default for <deny>
653 also, but here it means that the rule applies always, even when
654 not eavesdropping. The eavesdrop attribute can only be combined with
655 send and receive rules (with send_* and receive_* attributes).</para>
657 <para>The [send|receive]_requested_reply attribute works similarly to the eavesdrop
658 attribute. It controls whether the <deny> or <allow> matches a reply
659 that is expected (corresponds to a previous method call message).
660 This attribute only makes sense for reply messages (errors and method
661 returns), and is ignored for other message types.</para>
664 <para>For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
665 only requested replies are allowed by the
666 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
667 even if unexpected.</para>
670 <para>For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
671 the rule matches only when the reply was not
672 requested. [send|receive]_requested_reply="true" indicates that the rule applies
673 always, regardless of pending reply state.</para>
676 <para>user and group denials mean that the given user or group may
677 not connect to the message bus.</para>
680 <para>For "name", "username", "groupname", etc.
681 the character "*" can be substituted, meaning "any." Complex globs
682 like "foo.bar.*" aren't allowed for now because they'd be work to
683 implement and maybe encourage sloppy security anyway.</para>
686 <para><allow own_prefix="a.b"/> allows you to own the name "a.b" or any
687 name whose first dot-separated elements are "a.b": in particular,
688 you can own "a.b.c" or "a.b.c.d", but not "a.bc" or "a.c".
689 This is useful when services like Telepathy and ReserveDevice
690 define a meaning for subtrees of well-known names, such as
691 org.freedesktop.Telepathy.ConnectionManager.(anything)
692 and org.freedesktop.ReserveDevice1.(anything).</para>
695 <para>It does not make sense to deny a user or group inside a <policy>
696 for a user or group; user/group denials can only be inside
697 context="default" or context="mandatory" policies.</para>
700 <para>A single <deny> rule may specify combinations of attributes such as
701 send_destination and send_interface and send_type. In this case, the
702 denial applies only if both attributes match the message being denied.
703 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
704 deny messages with the given interface AND the given bus name.
705 To get an OR effect you specify multiple <deny> rules.</para>
708 <para>You can't include both send_ and receive_ attributes on the same
709 rule, since "whether the message can be sent" and "whether it can be
710 received" are evaluated separately.</para>
713 <para>Be careful with send_interface/receive_interface, because the
714 interface field in messages is optional. In particular, do NOT
715 specify <deny send_interface="org.foo.Bar"/>! This will cause
716 no-interface messages to be blocked for all services, which is
717 almost certainly not what you intended. Always use rules of
718 the form: <deny send_interface="org.foo.Bar" send_destination="org.foo.Service"/></para>
720 <itemizedlist remap='TP'>
722 <listitem><para><emphasis remap='I'><selinux></emphasis></para></listitem>
727 <para>The <selinux> element contains settings related to Security Enhanced Linux.
728 More details below.</para>
730 <itemizedlist remap='TP'>
732 <listitem><para><emphasis remap='I'><associate></emphasis></para></listitem>
737 <para>An <associate> element appears below an <selinux> element and
738 creates a mapping. Right now only one kind of association is possible:</para>
739 <literallayout remap='.nf'>
740 <associate own="org.freedesktop.Foobar" context="foo_t"/>
741 </literallayout> <!-- .fi -->
744 <para>This means that if a connection asks to own the name
745 "org.freedesktop.Foobar" then the source context will be the context
746 of the connection and the target context will be "foo_t" - see the
747 short discussion of SELinux below.</para>
750 <para>Note, the context here is the target context when requesting a name,
751 NOT the context of the connection owning the name.</para>
754 <para>There's currently no way to set a default for owning any name, if
755 we add this syntax it will look like:</para>
756 <literallayout remap='.nf'>
757 <associate own="*" context="foo_t"/>
758 </literallayout> <!-- .fi -->
759 <para>If you find a reason this is useful, let the developers know.
760 Right now the default will be the security context of the bus itself.</para>
763 <para>If two <associate> elements specify the same name, the element
764 appearing later in the configuration file will be used.</para>
768 <refsect1 id='selinux'><title>SELinux</title>
769 <para>See <ulink url='http://www.nsa.gov/selinux/'>http://www.nsa.gov/selinux/</ulink> for full details on SELinux. Some useful excerpts:</para>
772 <para>Every subject (process) and object (e.g. file, socket, IPC object,
773 etc) in the system is assigned a collection of security attributes,
774 known as a security context. A security context contains all of the
775 security attributes associated with a particular subject or object
776 that are relevant to the security policy.</para>
779 <para>In order to better encapsulate security contexts and to provide
780 greater efficiency, the policy enforcement code of SELinux typically
781 handles security identifiers (SIDs) rather than security contexts. A
782 SID is an integer that is mapped by the security server to a security
783 context at runtime.</para>
786 <para>When a security decision is required, the policy enforcement code
787 passes a pair of SIDs (typically the SID of a subject and the SID of
788 an object, but sometimes a pair of subject SIDs or a pair of object
789 SIDs), and an object security class to the security server. The object
790 security class indicates the kind of object, e.g. a process, a regular
791 file, a directory, a TCP socket, etc.</para>
794 <para>Access decisions specify whether or not a permission is granted for a
795 given pair of SIDs and class. Each object class has a set of
796 associated permissions defined to control operations on objects with
800 <para>D-Bus performs SELinux security checks in two places.</para>
803 <para>First, any time a message is routed from one connection to another
804 connection, the bus daemon will check permissions with the security context of
805 the first connection as source, security context of the second connection
806 as target, object class "dbus" and requested permission "send_msg".</para>
809 <para>If a security context is not available for a connection
810 (impossible when using UNIX domain sockets), then the target
811 context used is the context of the bus daemon itself.
812 There is currently no way to change this default, because we're
813 assuming that only UNIX domain sockets will be used to
814 connect to the systemwide bus. If this changes, we'll
815 probably add a way to set the default connection context.</para>
818 <para>Second, any time a connection asks to own a name,
819 the bus daemon will check permissions with the security
820 context of the connection as source, the security context specified
821 for the name in the config file as target, object
822 class "dbus" and requested permission "acquire_svc".</para>
825 <para>The security context for a bus name is specified with the
826 <associate> element described earlier in this document.
827 If a name has no security context associated in the
828 configuration file, the security context of the bus daemon
829 itself will be used.</para>
833 <refsect1 id='debugging'><title>DEBUGGING</title>
834 <para>If you're trying to figure out where your messages are going or why
835 you aren't getting messages, there are several things you can try.</para>
837 <para>Remember that the system bus is heavily locked down and if you
838 haven't installed a security policy file to allow your message
839 through, it won't work. For the session bus, this is not a concern.</para>
841 <para>The simplest way to figure out what's happening on the bus is to run
842 the <emphasis remap='I'>dbus-monitor</emphasis> program, which comes with the D-Bus
843 package. You can also send test messages with <emphasis remap='I'>dbus-send</emphasis>. These
844 programs have their own man pages.</para>
846 <para>If you want to know what the daemon itself is doing, you might consider
847 running a separate copy of the daemon to test against. This will allow you
848 to put the daemon under a debugger, or run it with verbose output, without
849 messing up your real session and system daemons.</para>
851 <para>To run a separate test copy of the daemon, for example you might open a terminal
853 <literallayout remap='.nf'>
854 DBUS_VERBOSE=1 dbus-daemon --session --print-address
855 </literallayout> <!-- .fi -->
857 <para>The test daemon address will be printed when the daemon starts. You will need
858 to copy-and-paste this address and use it as the value of the
859 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
860 you want to test. This will cause those applications to connect to your
861 test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.</para>
863 <para>DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
864 was compiled with verbose mode enabled. This is not recommended in
865 production builds due to performance impact. You may need to rebuild
866 D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
867 also affects the D-Bus library and thus applications using D-Bus; it may
868 be useful to see verbose output on both the client side and from the daemon.)</para>
870 <para>If you want to get fancy, you can create a custom bus
871 configuration for your test bus (see the session.conf and system.conf
872 files that define the two default configurations for example). This
873 would allow you to specify a different directory for .service files,
878 <refsect1 id='author'><title>AUTHOR</title>
879 <para>See <ulink url='http://www.freedesktop.org/software/dbus/doc/AUTHORS'>http://www.freedesktop.org/software/dbus/doc/AUTHORS</ulink></para>
883 <refsect1 id='bugs'><title>BUGS</title>
884 <para>Please send bug reports to the D-Bus mailing list or bug tracker,
885 see <ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink></para>