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_SYSCONFDIR@/dbus-1/session.conf" and the --system
54 option is equivalent to
55 "--config-file=@EXPANDED_SYSCONFDIR@/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_SYSCONFDIR@/dbus-1/system.conf" and
185 "@EXPANDED_SYSCONFDIR@/dbus-1/session.conf". These files normally
186 <include> a system-local.conf or session-local.conf; you can put local
187 overrides in those files to avoid modifying the primary configuration
191 <para>The configuration file is an XML document. It must have the following
192 doctype declaration:</para>
193 <literallayout remap='.nf'>
195 <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
196 "<ulink url='http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd'>http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd</ulink>">
198 </literallayout> <!-- .fi -->
201 <para>The following elements may be present in the configuration file.</para>
203 <itemizedlist remap='TP'>
205 <listitem><para><emphasis remap='I'><busconfig></emphasis></para></listitem>
210 <para>Root element.</para>
212 <itemizedlist remap='TP'>
214 <listitem><para><emphasis remap='I'><type></emphasis></para></listitem>
219 <para>The well-known type of the message bus. Currently known values are
220 "system" and "session"; if other values are set, they should be
221 either added to the D-Bus specification, or namespaced. The last
222 <type> element "wins" (previous values are ignored). This element
223 only controls which message bus specific environment variables are
224 set in activated clients. Most of the policy that distinguishes a
225 session bus from the system bus is controlled from the other elements
226 in the configuration file.</para>
229 <para>If the well-known type of the message bus is "session", then the
230 DBUS_STARTER_BUS_TYPE environment variable will be set to "session"
231 and the DBUS_SESSION_BUS_ADDRESS environment variable will be set
232 to the address of the session bus. Likewise, if the type of the
233 message bus is "system", then the DBUS_STARTER_BUS_TYPE environment
234 variable will be set to "system" and the DBUS_SESSION_BUS_ADDRESS
235 environment variable will be set to the address of the system bus
236 (which is normally well known anyway).</para>
239 <para>Example: <type>session</type></para>
241 <itemizedlist remap='TP'>
243 <listitem><para><emphasis remap='I'><include></emphasis></para></listitem>
248 <para>Include a file <include>filename.conf</include> at this point. If the
249 filename is relative, it is located relative to the configuration file
250 doing the including.</para>
253 <para><include> has an optional attribute "ignore_missing=(yes|no)"
254 which defaults to "no" if not provided. This attribute
255 controls whether it's a fatal error for the included file
258 <itemizedlist remap='TP'>
260 <listitem><para><emphasis remap='I'><includedir></emphasis></para></listitem>
265 <para>Include all files in <includedir>foo.d</includedir> at this
266 point. Files in the directory are included in undefined order.
267 Only files ending in ".conf" are included.</para>
270 <para>This is intended to allow extension of the system bus by particular
271 packages. For example, if CUPS wants to be able to send out
272 notification of printer queue changes, it could install a file to
273 @EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
274 this message and allowed the printer daemon user to send it.</para>
276 <itemizedlist remap='TP'>
278 <listitem><para><emphasis remap='I'><user></emphasis></para></listitem>
283 <para>The user account the daemon should run as, as either a username or a
284 UID. If the daemon cannot change to this UID on startup, it will exit.
285 If this element is not present, the daemon will not change or care
286 about its UID.</para>
289 <para>The last <user> entry in the file "wins", the others are ignored.</para>
292 <para>The user is changed after the bus has completed initialization. So
293 sockets etc. will be created before changing user, but no data will be
294 read from clients before changing user. This means that sockets
295 and PID files can be created in a location that requires root
296 privileges for writing.</para>
298 <itemizedlist remap='TP'>
300 <listitem><para><emphasis remap='I'><fork></emphasis></para></listitem>
305 <para>If present, the bus daemon becomes a real daemon (forks
306 into the background, etc.). This is generally used
307 rather than the --fork command line option.</para>
309 <itemizedlist remap='TP'>
311 <listitem><para><emphasis remap='I'><keep_umask></emphasis></para></listitem>
316 <para>If present, the bus daemon keeps its original umask when forking.
317 This may be useful to avoid affecting the behavior of child processes.</para>
319 <itemizedlist remap='TP'>
321 <listitem><para><emphasis remap='I'><listen></emphasis></para></listitem>
326 <para>Add an address that the bus should listen on. The
327 address is in the standard D-Bus format that contains
328 a transport name plus possible parameters/options.</para>
331 <para>Example: <listen>unix:path=/tmp/foo</listen></para>
334 <para>Example: <listen>tcp:host=localhost,port=1234</listen></para>
337 <para>If there are multiple <listen> elements, then the bus listens
338 on multiple addresses. The bus will pass its address to
339 started services or other interested parties with
340 the last address given in <listen> first. That is,
341 apps will try to connect to the last <listen> address first.</para>
344 <para>tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.
345 If a hostname resolves to multiple addresses, the server will bind
346 to all of them. The family=ipv4 or family=ipv6 options can be used
347 to force it to bind to a subset of addresses</para>
350 <para>Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen></para>
353 <para>A special case is using a port number of zero (or omitting the port),
354 which means to choose an available port selected by the operating
355 system. The port number chosen can be obtained with the
356 --print-address command line parameter and will be present in other
357 cases where the server reports its own address, such as when
358 DBUS_SESSION_BUS_ADDRESS is set.</para>
361 <para>Example: <listen>tcp:host=localhost,port=0</listen></para>
364 <para>tcp addresses also allow a bind=hostname option, which will override
365 the host option specifying what address to bind to, without changing
366 the address reported by the bus. The bind option can also take a
367 special name '*' to cause the bus to listen on all local address
368 (INADDR_ANY). The specified host should be a valid name of the local
369 machine or weird stuff will happen.</para>
372 <para>Example: <listen>tcp:host=localhost,bind=*,port=0</listen></para>
374 <itemizedlist remap='TP'>
376 <listitem><para><emphasis remap='I'><auth></emphasis></para></listitem>
381 <para>Lists permitted authorization mechanisms. If this element doesn't
382 exist, then all known mechanisms are allowed. If there are multiple
383 <auth> elements, all the listed mechanisms are allowed. The order in
384 which mechanisms are listed is not meaningful.</para>
387 <para>Example: <auth>EXTERNAL</auth></para>
390 <para>Example: <auth>DBUS_COOKIE_SHA1</auth></para>
392 <itemizedlist remap='TP'>
394 <listitem><para><emphasis remap='I'><servicedir></emphasis></para></listitem>
399 <para>Adds a directory to scan for .service files. Directories are
400 scanned starting with the last to appear in the config file
401 (the first .service file found that provides a particular
402 service will be used).</para>
405 <para>Service files tell the bus how to automatically start a program.
406 They are primarily used with the per-user-session bus,
407 not the systemwide bus.</para>
409 <itemizedlist remap='TP'>
411 <listitem><para><emphasis remap='I'><standard_session_servicedirs/></emphasis></para></listitem>
416 <para><standard_session_servicedirs/> is equivalent to specifying a series
417 of <servicedir/> elements for each of the data directories in the "XDG
418 Base Directory Specification" with the subdirectory "dbus-1/services",
419 so for example "/usr/share/dbus-1/services" would be among the
420 directories searched.</para>
423 <para>The "XDG Base Directory Specification" can be found at
424 <ulink url='http://freedesktop.org/wiki/Standards/basedir-spec'>http://freedesktop.org/wiki/Standards/basedir-spec</ulink> if it hasn't moved,
425 otherwise try your favorite search engine.</para>
428 <para>The <standard_session_servicedirs/> option is only relevant to the
429 per-user-session bus daemon defined in
430 @EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
431 configuration file would probably be nonsense.</para>
433 <itemizedlist remap='TP'>
435 <listitem><para><emphasis remap='I'><standard_system_servicedirs/></emphasis></para></listitem>
440 <para><standard_system_servicedirs/> specifies the standard system-wide
441 activation directories that should be searched for service files.
442 This option defaults to @EXPANDED_DATADIR@/dbus-1/system-services.</para>
445 <para>The <standard_system_servicedirs/> option is only relevant to the
446 per-system bus daemon defined in
447 @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
448 configuration file would probably be nonsense.</para>
450 <itemizedlist remap='TP'>
452 <listitem><para><emphasis remap='I'><servicehelper/></emphasis></para></listitem>
457 <para><servicehelper/> specifies the setuid helper that is used to launch
458 system daemons with an alternate user. Typically this should be
459 the dbus-daemon-launch-helper executable in located in libexec.</para>
462 <para>The <servicehelper/> option is only relevant to the per-system bus daemon
463 defined in @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
464 configuration file would probably be nonsense.</para>
466 <itemizedlist remap='TP'>
468 <listitem><para><emphasis remap='I'><limit></emphasis></para></listitem>
473 <para><limit> establishes a resource limit. For example:</para>
474 <literallayout remap='.nf'>
475 <limit name="max_message_size">64</limit>
476 <limit name="max_completed_connections">512</limit>
477 </literallayout> <!-- .fi -->
480 <para>The name attribute is mandatory.
481 Available limit names are:</para>
482 <literallayout remap='.nf'>
483 "max_incoming_bytes" : total size in bytes of messages
484 incoming from a single connection
485 "max_incoming_unix_fds" : total number of unix fds of messages
486 incoming from a single connection
487 "max_outgoing_bytes" : total size in bytes of messages
488 queued up for a single connection
489 "max_outgoing_unix_fds" : total number of unix fds of messages
490 queued up for a single connection
491 "max_message_size" : max size of a single message in
493 "max_message_unix_fds" : max unix fds of a single message
494 "service_start_timeout" : milliseconds (thousandths) until
495 a started service has to connect
496 "auth_timeout" : milliseconds (thousandths) a
497 connection is given to
499 "max_completed_connections" : max number of authenticated connections
500 "max_incomplete_connections" : max number of unauthenticated
502 "max_connections_per_user" : max number of completed connections from
504 "max_pending_service_starts" : max number of service launches in
505 progress at the same time
506 "max_names_per_connection" : max number of names a single
508 "max_match_rules_per_connection": max number of match rules for a single
510 "max_replies_per_connection" : max number of pending method
511 replies per connection
512 (number of calls-in-progress)
513 "reply_timeout" : milliseconds (thousandths)
514 until a method call times out
515 </literallayout> <!-- .fi -->
518 <para>The max incoming/outgoing queue sizes allow a new message to be queued
519 if one byte remains below the max. So you can in fact exceed the max
520 by max_message_size.</para>
523 <para>max_completed_connections divided by max_connections_per_user is the
524 number of users that can work together to denial-of-service all other users by using
525 up all connections on the systemwide bus.</para>
528 <para>Limits are normally only of interest on the systemwide bus, not the user session
531 <itemizedlist remap='TP'>
533 <listitem><para><emphasis remap='I'><policy></emphasis></para></listitem>
538 <para>The <policy> element defines a security policy to be applied to a particular
539 set of connections to the bus. A policy is made up of
540 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
541 they are analogous to a firewall in that they allow expected traffic
542 and prevent unexpected traffic.</para>
545 <para>Currently, the system bus has a default-deny policy for sending method calls
546 and owning bus names. Everything else, in particular reply messages, receive
547 checks, and signals has a default allow policy.</para>
550 <para>In general, it is best to keep system services as small, targeted programs which
551 run in their own process and provide a single bus name. Then, all that is needed
552 is an <allow> rule for the "own" permission to let the process claim the bus
553 name, and a "send_destination" rule to allow traffic from some or all uids to
557 <para>The <policy> element has one of four attributes:</para>
558 <literallayout remap='.nf'>
559 context="(default|mandatory)"
560 at_console="(true|false)"
561 user="username or userid"
562 group="group name or gid"
563 </literallayout> <!-- .fi -->
566 <para>Policies are applied to a connection as follows:</para>
567 <literallayout remap='.nf'>
568 - all context="default" policies are applied
569 - all group="connection's user's group" policies are applied
571 - all user="connection's auth user" policies are applied
573 - all at_console="true" policies are applied
574 - all at_console="false" policies are applied
575 - all context="mandatory" policies are applied
576 </literallayout> <!-- .fi -->
579 <para>Policies applied later will override those applied earlier,
580 when the policies overlap. Multiple policies with the same
581 user/group/context are applied in the order they appear
582 in the config file.</para>
584 <variablelist remap='TP'>
586 <term><emphasis remap='I'><deny></emphasis></term>
588 <para><emphasis remap='I'><allow></emphasis></para>
594 <para>A <deny> element appears below a <policy> element and prohibits some
595 action. The <allow> element makes an exception to previous <deny>
596 statements, and works just like <deny> but with the inverse meaning.</para>
599 <para>The possible attributes of these elements are:</para>
600 <literallayout remap='.nf'>
601 send_interface="interface_name"
602 send_member="method_or_signal_name"
603 send_error="error_name"
604 send_destination="name"
605 send_type="method_call" | "method_return" | "signal" | "error"
606 send_path="/path/name"
608 receive_interface="interface_name"
609 receive_member="method_or_signal_name"
610 receive_error="error_name"
611 receive_sender="name"
612 receive_type="method_call" | "method_return" | "signal" | "error"
613 receive_path="/path/name"
615 send_requested_reply="true" | "false"
616 receive_requested_reply="true" | "false"
618 eavesdrop="true" | "false"
624 </literallayout> <!-- .fi -->
627 <para>Examples:</para>
628 <literallayout remap='.nf'>
629 <deny send_destination="org.freedesktop.Service" send_interface="org.freedesktop.System" send_member="Reboot"/>
630 <deny send_destination="org.freedesktop.System"/>
631 <deny receive_sender="org.freedesktop.System"/>
632 <deny user="john"/>
633 <deny group="enemies"/>
634 </literallayout> <!-- .fi -->
637 <para>The <deny> element's attributes determine whether the deny "matches" a
638 particular action. If it matches, the action is denied (unless later
639 rules in the config file allow it).</para>
641 <para>send_destination and receive_sender rules mean that messages may not be
642 sent to or received from the *owner* of the given name, not that
643 they may not be sent *to that name*. That is, if a connection
644 owns services A, B, C, and sending to A is denied, sending to B or C
645 will not work either.</para>
647 <para>The other send_* and receive_* attributes are purely textual/by-value
648 matches against the given field in the message header.</para>
650 <para>"Eavesdropping" occurs when an application receives a message that
651 was explicitly addressed to a name the application does not own, or
652 is a reply to such a message. Eavesdropping thus only applies to
653 messages that are addressed to services and replies to such messages
654 (i.e. it does not apply to signals).</para>
656 <para>For <allow>, eavesdrop="true" indicates that the rule matches even
657 when eavesdropping. eavesdrop="false" is the default and means that
658 the rule only allows messages to go to their specified recipient.
659 For <deny>, eavesdrop="true" indicates that the rule matches
660 only when eavesdropping. eavesdrop="false" is the default for <deny>
661 also, but here it means that the rule applies always, even when
662 not eavesdropping. The eavesdrop attribute can only be combined with
663 send and receive rules (with send_* and receive_* attributes).</para>
665 <para>The [send|receive]_requested_reply attribute works similarly to the eavesdrop
666 attribute. It controls whether the <deny> or <allow> matches a reply
667 that is expected (corresponds to a previous method call message).
668 This attribute only makes sense for reply messages (errors and method
669 returns), and is ignored for other message types.</para>
672 <para>For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
673 only requested replies are allowed by the
674 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
675 even if unexpected.</para>
678 <para>For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
679 the rule matches only when the reply was not
680 requested. [send|receive]_requested_reply="true" indicates that the rule applies
681 always, regardless of pending reply state.</para>
684 <para>user and group denials mean that the given user or group may
685 not connect to the message bus.</para>
688 <para>For "name", "username", "groupname", etc.
689 the character "*" can be substituted, meaning "any." Complex globs
690 like "foo.bar.*" aren't allowed for now because they'd be work to
691 implement and maybe encourage sloppy security anyway.</para>
694 <para><allow own_prefix="a.b"/> allows you to own the name "a.b" or any
695 name whose first dot-separated elements are "a.b": in particular,
696 you can own "a.b.c" or "a.b.c.d", but not "a.bc" or "a.c".
697 This is useful when services like Telepathy and ReserveDevice
698 define a meaning for subtrees of well-known names, such as
699 org.freedesktop.Telepathy.ConnectionManager.(anything)
700 and org.freedesktop.ReserveDevice1.(anything).</para>
703 <para>It does not make sense to deny a user or group inside a <policy>
704 for a user or group; user/group denials can only be inside
705 context="default" or context="mandatory" policies.</para>
708 <para>A single <deny> rule may specify combinations of attributes such as
709 send_destination and send_interface and send_type. In this case, the
710 denial applies only if both attributes match the message being denied.
711 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
712 deny messages with the given interface AND the given bus name.
713 To get an OR effect you specify multiple <deny> rules.</para>
716 <para>You can't include both send_ and receive_ attributes on the same
717 rule, since "whether the message can be sent" and "whether it can be
718 received" are evaluated separately.</para>
721 <para>Be careful with send_interface/receive_interface, because the
722 interface field in messages is optional. In particular, do NOT
723 specify <deny send_interface="org.foo.Bar"/>! This will cause
724 no-interface messages to be blocked for all services, which is
725 almost certainly not what you intended. Always use rules of
726 the form: <deny send_interface="org.foo.Bar" send_destination="org.foo.Service"/></para>
728 <itemizedlist remap='TP'>
730 <listitem><para><emphasis remap='I'><selinux></emphasis></para></listitem>
735 <para>The <selinux> element contains settings related to Security Enhanced Linux.
736 More details below.</para>
738 <itemizedlist remap='TP'>
740 <listitem><para><emphasis remap='I'><associate></emphasis></para></listitem>
745 <para>An <associate> element appears below an <selinux> element and
746 creates a mapping. Right now only one kind of association is possible:</para>
747 <literallayout remap='.nf'>
748 <associate own="org.freedesktop.Foobar" context="foo_t"/>
749 </literallayout> <!-- .fi -->
752 <para>This means that if a connection asks to own the name
753 "org.freedesktop.Foobar" then the source context will be the context
754 of the connection and the target context will be "foo_t" - see the
755 short discussion of SELinux below.</para>
758 <para>Note, the context here is the target context when requesting a name,
759 NOT the context of the connection owning the name.</para>
762 <para>There's currently no way to set a default for owning any name, if
763 we add this syntax it will look like:</para>
764 <literallayout remap='.nf'>
765 <associate own="*" context="foo_t"/>
766 </literallayout> <!-- .fi -->
767 <para>If you find a reason this is useful, let the developers know.
768 Right now the default will be the security context of the bus itself.</para>
771 <para>If two <associate> elements specify the same name, the element
772 appearing later in the configuration file will be used.</para>
776 <refsect1 id='selinux'><title>SELinux</title>
777 <para>See <ulink url='http://www.nsa.gov/selinux/'>http://www.nsa.gov/selinux/</ulink> for full details on SELinux. Some useful excerpts:</para>
780 <para>Every subject (process) and object (e.g. file, socket, IPC object,
781 etc) in the system is assigned a collection of security attributes,
782 known as a security context. A security context contains all of the
783 security attributes associated with a particular subject or object
784 that are relevant to the security policy.</para>
787 <para>In order to better encapsulate security contexts and to provide
788 greater efficiency, the policy enforcement code of SELinux typically
789 handles security identifiers (SIDs) rather than security contexts. A
790 SID is an integer that is mapped by the security server to a security
791 context at runtime.</para>
794 <para>When a security decision is required, the policy enforcement code
795 passes a pair of SIDs (typically the SID of a subject and the SID of
796 an object, but sometimes a pair of subject SIDs or a pair of object
797 SIDs), and an object security class to the security server. The object
798 security class indicates the kind of object, e.g. a process, a regular
799 file, a directory, a TCP socket, etc.</para>
802 <para>Access decisions specify whether or not a permission is granted for a
803 given pair of SIDs and class. Each object class has a set of
804 associated permissions defined to control operations on objects with
808 <para>D-Bus performs SELinux security checks in two places.</para>
811 <para>First, any time a message is routed from one connection to another
812 connection, the bus daemon will check permissions with the security context of
813 the first connection as source, security context of the second connection
814 as target, object class "dbus" and requested permission "send_msg".</para>
817 <para>If a security context is not available for a connection
818 (impossible when using UNIX domain sockets), then the target
819 context used is the context of the bus daemon itself.
820 There is currently no way to change this default, because we're
821 assuming that only UNIX domain sockets will be used to
822 connect to the systemwide bus. If this changes, we'll
823 probably add a way to set the default connection context.</para>
826 <para>Second, any time a connection asks to own a name,
827 the bus daemon will check permissions with the security
828 context of the connection as source, the security context specified
829 for the name in the config file as target, object
830 class "dbus" and requested permission "acquire_svc".</para>
833 <para>The security context for a bus name is specified with the
834 <associate> element described earlier in this document.
835 If a name has no security context associated in the
836 configuration file, the security context of the bus daemon
837 itself will be used.</para>
841 <refsect1 id='debugging'><title>DEBUGGING</title>
842 <para>If you're trying to figure out where your messages are going or why
843 you aren't getting messages, there are several things you can try.</para>
845 <para>Remember that the system bus is heavily locked down and if you
846 haven't installed a security policy file to allow your message
847 through, it won't work. For the session bus, this is not a concern.</para>
849 <para>The simplest way to figure out what's happening on the bus is to run
850 the <emphasis remap='I'>dbus-monitor</emphasis> program, which comes with the D-Bus
851 package. You can also send test messages with <emphasis remap='I'>dbus-send</emphasis>. These
852 programs have their own man pages.</para>
854 <para>If you want to know what the daemon itself is doing, you might consider
855 running a separate copy of the daemon to test against. This will allow you
856 to put the daemon under a debugger, or run it with verbose output, without
857 messing up your real session and system daemons.</para>
859 <para>To run a separate test copy of the daemon, for example you might open a terminal
861 <literallayout remap='.nf'>
862 DBUS_VERBOSE=1 dbus-daemon --session --print-address
863 </literallayout> <!-- .fi -->
865 <para>The test daemon address will be printed when the daemon starts. You will need
866 to copy-and-paste this address and use it as the value of the
867 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
868 you want to test. This will cause those applications to connect to your
869 test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.</para>
871 <para>DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
872 was compiled with verbose mode enabled. This is not recommended in
873 production builds due to performance impact. You may need to rebuild
874 D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
875 also affects the D-Bus library and thus applications using D-Bus; it may
876 be useful to see verbose output on both the client side and from the daemon.)</para>
878 <para>If you want to get fancy, you can create a custom bus
879 configuration for your test bus (see the session.conf and system.conf
880 files that define the two default configurations for example). This
881 would allow you to specify a different directory for .service files,
886 <refsect1 id='author'><title>AUTHOR</title>
887 <para>See <ulink url='http://www.freedesktop.org/software/dbus/doc/AUTHORS'>http://www.freedesktop.org/software/dbus/doc/AUTHORS</ulink></para>
891 <refsect1 id='bugs'><title>BUGS</title>
892 <para>Please send bug reports to the D-Bus mailing list or bug tracker,
893 see <ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink></para>