2 .\" dbus-daemon manual page.
3 .\" Copyright (C) 2003 Red Hat, Inc.
7 dbus-daemon \- Message bus daemon
11 dbus-daemon [\-\-version] [\-\-session] [\-\-system] [\-\-config-file=FILE]
12 [\-\-print-address[=DESCRIPTOR]] [\-\-print-pid[=DESCRIPTOR]] [\-\-fork]
16 \fIdbus-daemon\fP is the D-Bus message bus daemon. See
17 http://www.freedesktop.org/software/dbus/ for more information about
18 the big picture. D-Bus is first a library that provides one-to-one
19 communication between any two applications; \fIdbus-daemon\fP is an
20 application that uses this library to implement a message bus
21 daemon. Multiple programs connect to the message bus daemon and can
22 exchange messages with one another.
25 There are two standard message bus instances: the systemwide message bus
26 (installed on many systems as the "messagebus" init service) and the
27 per-user-login-session message bus (started each time a user logs in).
28 \fIdbus-daemon\fP is used for both of these instances, but with
29 a different configuration file.
32 The \-\-session option is equivalent to
33 "\-\-config-file=@EXPANDED_SYSCONFDIR@/dbus-1/session.conf" and the \-\-system
34 option is equivalent to
35 "\-\-config-file=@EXPANDED_SYSCONFDIR@/dbus-1/system.conf". By creating
36 additional configuration files and using the \-\-config-file option,
37 additional special-purpose message bus daemons could be created.
40 The systemwide daemon is normally launched by an init script,
41 standardly called simply "messagebus".
44 The systemwide daemon is largely used for broadcasting system events,
45 such as changes to the printer queue, or adding/removing devices.
48 The per-session daemon is used for various interprocess communication
49 among desktop applications (however, it is not tied to X or the GUI
53 SIGHUP will cause the D-Bus daemon to PARTIALLY reload its
54 configuration file and to flush its user/group information caches. Some
55 configuration changes would require kicking all apps off the bus; so they will
56 only take effect if you restart the daemon. Policy changes should take effect
60 The following options are supported:
62 .I "--config-file=FILE"
63 Use the given configuration file.
66 Force the message bus to fork and become a daemon, even if
67 the configuration file does not specify that it should.
68 In most contexts the configuration file already gets this
71 .I "--print-address[=DESCRIPTOR]"
72 Print the address of the message bus to standard output, or
73 to the given file descriptor. This is used by programs that
74 launch the message bus.
76 .I "--print-pid[=DESCRIPTOR]"
77 Print the process ID of the message bus to standard output, or
78 to the given file descriptor. This is used by programs that
79 launch the message bus.
82 Use the standard configuration file for the per-login-session message
86 Use the standard configuration file for the systemwide message bus.
89 Print the version of the daemon.
91 .SH CONFIGURATION FILE
93 A message bus daemon has a configuration file that specializes it
94 for a particular application. For example, one configuration
95 file might set up the message bus to be a systemwide message bus,
96 while another might set it up to be a per-user-login-session bus.
99 The configuration file also establishes resource limits, security
100 parameters, and so forth.
103 The configuration file is not part of any interoperability
104 specification and its backward compatibility is not guaranteed; this
105 document is documentation, not specification.
108 The standard systemwide and per-session message bus setups are
109 configured in the files "@EXPANDED_SYSCONFDIR@/dbus-1/system.conf" and
110 "@EXPANDED_SYSCONFDIR@/dbus-1/session.conf". These files normally
111 <include> a system-local.conf or session-local.conf; you can put local
112 overrides in those files to avoid modifying the primary configuration
116 The configuration file is an XML document. It must have the following
120 <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
121 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
126 The following elements may be present in the configuration file.
138 The well-known type of the message bus. Currently known values are
139 "system" and "session"; if other values are set, they should be
140 either added to the D-Bus specification, or namespaced. The last
141 <type> element "wins" (previous values are ignored). This element
142 only controls which message bus specific environment variables are
143 set in activated clients. Most of the policy that distinguishes a
144 session bus from the system bus is controlled from the other elements
145 in the configuration file.
148 If the well-known type of the message bus is "session", then the
149 DBUS_STARTER_BUS_TYPE environment variable will be set to "session"
150 and the DBUS_SESSION_BUS_ADDRESS environment variable will be set
151 to the address of the session bus. Likewise, if the type of the
152 message bus is "system", then the DBUS_STARTER_BUS_TYPE environment
153 variable will be set to "system" and the DBUS_SESSION_BUS_ADDRESS
154 environment variable will be set to the address of the system bus
155 (which is normally well known anyway).
158 Example: <type>session</type>
164 Include a file <include>filename.conf</include> at this point. If the
165 filename is relative, it is located relative to the configuration file
169 <include> has an optional attribute "ignore_missing=(yes|no)"
170 which defaults to "no" if not provided. This attribute
171 controls whether it's a fatal error for the included file
178 Include all files in <includedir>foo.d</includedir> at this
179 point. Files in the directory are included in undefined order.
180 Only files ending in ".conf" are included.
183 This is intended to allow extension of the system bus by particular
184 packages. For example, if CUPS wants to be able to send out
185 notification of printer queue changes, it could install a file to
186 @EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
187 this message and allowed the printer daemon user to send it.
193 The user account the daemon should run as, as either a username or a
194 UID. If the daemon cannot change to this UID on startup, it will exit.
195 If this element is not present, the daemon will not change or care
199 The last <user> entry in the file "wins", the others are ignored.
202 The user is changed after the bus has completed initialization. So
203 sockets etc. will be created before changing user, but no data will be
204 read from clients before changing user. This means that sockets
205 and PID files can be created in a location that requires root
206 privileges for writing.
212 If present, the bus daemon becomes a real daemon (forks
213 into the background, etc.). This is generally used
214 rather than the \-\-fork command line option.
220 Add an address that the bus should listen on. The
221 address is in the standard D-Bus format that contains
222 a transport name plus possible parameters/options.
225 Example: <listen>unix:path=/tmp/foo</listen>
228 Example: <listen>tcp:host=localhost,port=1234</listen>
231 If there are multiple <listen> elements, then the bus listens
232 on multiple addresses. The bus will pass its address to
233 started services or other interested parties with
234 the last address given in <listen> first. That is,
235 apps will try to connect to the last <listen> address first.
238 tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.
239 If a hostname resolves to multiple addresses, the server will bind
240 to all of them. The family=ipv4 or family=ipv6 options can be used
241 to force it to bind to a subset of addresses
244 Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen>
247 A special case is using a port number of zero (or omitting the port),
248 which means to choose an available port selected by the operating
249 system. The port number chosen can be obtained with the
250 --print-address command line parameter and will be present in other
251 cases where the server reports its own address, such as when
252 DBUS_SESSION_BUS_ADDRESS is set.
255 Example: <listen>tcp:host=localhost,port=0</listen>
258 tcp addresses also allow a bind=hostname option, which will override
259 the host option specifying what address to bind to, without changing
260 the address reported by the bus. The bind option can also take a
261 special name '*' to cause the bus to listen on all local address
262 (INADDR_ANY). The specified host should be a valid name of the local
263 machine or weird stuff will happen.
266 Example: <listen>tcp:host=localhost,bind=*,port=0</listen>
272 Lists permitted authorization mechanisms. If this element doesn't
273 exist, then all known mechanisms are allowed. If there are multiple
274 <auth> elements, all the listed mechanisms are allowed. The order in
275 which mechanisms are listed is not meaningful.
278 Example: <auth>EXTERNAL</auth>
281 Example: <auth>DBUS_COOKIE_SHA1</auth>
287 Adds a directory to scan for .service files. Directories are
288 scanned starting with the last to appear in the config file
289 (the first .service file found that provides a particular
290 service will be used).
293 Service files tell the bus how to automatically start a program.
294 They are primarily used with the per-user-session bus,
295 not the systemwide bus.
298 .I "<standard_session_servicedirs/>"
301 <standard_session_servicedirs/> is equivalent to specifying a series
302 of <servicedir/> elements for each of the data directories in the "XDG
303 Base Directory Specification" with the subdirectory "dbus-1/services",
304 so for example "/usr/share/dbus-1/services" would be among the
305 directories searched.
308 The "XDG Base Directory Specification" can be found at
309 http://freedesktop.org/wiki/Standards/basedir-spec if it hasn't moved,
310 otherwise try your favorite search engine.
313 The <standard_session_servicedirs/> option is only relevant to the
314 per-user-session bus daemon defined in
315 @EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
316 configuration file would probably be nonsense.
319 .I "<standard_system_servicedirs/>"
322 <standard_system_servicedirs/> specifies the standard system-wide
323 activation directories that should be searched for service files.
324 This option defaults to @EXPANDED_DATADIR@/dbus-1/system-services.
327 The <standard_system_servicedirs/> option is only relevant to the
328 per-system bus daemon defined in
329 @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
330 configuration file would probably be nonsense.
333 .I "<servicehelper/>"
336 <servicehelper/> specifies the setuid helper that is used to launch
337 system daemons with an alternate user. Typically this should be
338 the dbus-daemon-launch-helper executable in located in libexec.
341 The <servicehelper/> option is only relevant to the per-system bus daemon
342 defined in @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
343 configuration file would probably be nonsense.
349 <limit> establishes a resource limit. For example:
351 <limit name="max_message_size">64</limit>
352 <limit name="max_completed_connections">512</limit>
356 The name attribute is mandatory.
357 Available limit names are:
359 "max_incoming_bytes" : total size in bytes of messages
360 incoming from a single connection
361 "max_outgoing_bytes" : total size in bytes of messages
362 queued up for a single connection
363 "max_message_size" : max size of a single message in
365 "service_start_timeout" : milliseconds (thousandths) until
366 a started service has to connect
367 "auth_timeout" : milliseconds (thousandths) a
368 connection is given to
370 "max_completed_connections" : max number of authenticated connections
371 "max_incomplete_connections" : max number of unauthenticated
373 "max_connections_per_user" : max number of completed connections from
375 "max_pending_service_starts" : max number of service launches in
376 progress at the same time
377 "max_names_per_connection" : max number of names a single
379 "max_match_rules_per_connection": max number of match rules for a single
381 "max_replies_per_connection" : max number of pending method
382 replies per connection
383 (number of calls-in-progress)
384 "reply_timeout" : milliseconds (thousandths)
385 until a method call times out
389 The max incoming/outgoing queue sizes allow a new message to be queued
390 if one byte remains below the max. So you can in fact exceed the max
394 max_completed_connections divided by max_connections_per_user is the
395 number of users that can work together to denial-of-service all other users by using
396 up all connections on the systemwide bus.
399 Limits are normally only of interest on the systemwide bus, not the user session
406 The <policy> element defines a security policy to be applied to a particular
407 set of connections to the bus. A policy is made up of
408 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
409 they are analogous to a firewall in that they allow expected traffic
410 and prevent unexpected traffic.
413 The <policy> element has one of three attributes:
415 context="(default|mandatory)"
416 user="username or userid"
417 group="group name or gid"
422 Policies are applied to a connection as follows:
424 - all context="default" policies are applied
425 - all group="connection's user's group" policies are applied
427 - all user="connection's auth user" policies are applied
429 - all context="mandatory" policies are applied
433 Policies applied later will override those applied earlier,
434 when the policies overlap. Multiple policies with the same
435 user/group/context are applied in the order they appear
443 A <deny> element appears below a <policy> element and prohibits some
444 action. The <allow> element makes an exception to previous <deny>
445 statements, and works just like <deny> but with the inverse meaning.
448 The possible attributes of these elements are:
450 send_interface="interface_name"
451 send_member="method_or_signal_name"
452 send_error="error_name"
453 send_destination="name"
454 send_type="method_call" | "method_return" | "signal" | "error"
455 send_path="/path/name"
457 receive_interface="interface_name"
458 receive_member="method_or_signal_name"
459 receive_error="error_name"
460 receive_sender="name"
461 receive_type="method_call" | "method_return" | "signal" | "error"
462 receive_path="/path/name"
464 send_requested_reply="true" | "false"
465 receive_requested_reply="true" | "false"
467 eavesdrop="true" | "false"
477 <deny send_interface="org.freedesktop.System" send_member="Reboot"/>
478 <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
479 <deny own="org.freedesktop.System"/>
480 <deny send_destination="org.freedesktop.System"/>
481 <deny receive_sender="org.freedesktop.System"/>
483 <deny group="enemies"/>
487 The <deny> element's attributes determine whether the deny "matches" a
488 particular action. If it matches, the action is denied (unless later
489 rules in the config file allow it).
492 send_destination and receive_sender rules mean that messages may not be
493 sent to or received from the *owner* of the given name, not that
494 they may not be sent *to that name*. That is, if a connection
495 owns services A, B, C, and sending to A is denied, sending to B or C
496 will not work either.
499 The other send_* and receive_* attributes are purely textual/by-value
500 matches against the given field in the message header.
503 "Eavesdropping" occurs when an application receives a message that
504 was explicitly addressed to a name the application does not own, or
505 is a reply to such a message. Eavesdropping thus only applies to
506 messages that are addressed to services and replies to such messages
507 (i.e. it does not apply to signals).
510 For <allow>, eavesdrop="true" indicates that the rule matches even
511 when eavesdropping. eavesdrop="false" is the default and means that
512 the rule only allows messages to go to their specified recipient.
513 For <deny>, eavesdrop="true" indicates that the rule matches
514 only when eavesdropping. eavesdrop="false" is the default for <deny>
515 also, but here it means that the rule applies always, even when
516 not eavesdropping. The eavesdrop attribute can only be combined with
517 send and receive rules (with send_* and receive_* attributes).
521 The [send|receive]_requested_reply attribute works similarly to the eavesdrop
522 attribute. It controls whether the <deny> or <allow> matches a reply
523 that is expected (corresponds to a previous method call message).
524 This attribute only makes sense for reply messages (errors and method
525 returns), and is ignored for other message types.
528 For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
529 only requested replies are allowed by the
530 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
534 For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
535 the rule matches only when the reply was not
536 requested. [send|receive]_requested_reply="true" indicates that the rule applies
537 always, regardless of pending reply state.
540 user and group denials mean that the given user or group may
541 not connect to the message bus.
544 For "name", "username", "groupname", etc.
545 the character "*" can be substituted, meaning "any." Complex globs
546 like "foo.bar.*" aren't allowed for now because they'd be work to
547 implement and maybe encourage sloppy security anyway.
550 It does not make sense to deny a user or group inside a <policy>
551 for a user or group; user/group denials can only be inside
552 context="default" or context="mandatory" policies.
555 A single <deny> rule may specify combinations of attributes such as
556 send_destination and send_interface and send_type. In this case, the
557 denial applies only if both attributes match the message being denied.
558 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
559 deny messages with the given interface AND the given bus name.
560 To get an OR effect you specify multiple <deny> rules.
563 You can't include both send_ and receive_ attributes on the same
564 rule, since "whether the message can be sent" and "whether it can be
565 received" are evaluated separately.
568 Be careful with send_interface/receive_interface, because the
569 interface field in messages is optional.
575 The <selinux> element contains settings related to Security Enhanced Linux.
582 An <associate> element appears below an <selinux> element and
583 creates a mapping. Right now only one kind of association is possible:
585 <associate own="org.freedesktop.Foobar" context="foo_t"/>
589 This means that if a connection asks to own the name
590 "org.freedesktop.Foobar" then the source context will be the context
591 of the connection and the target context will be "foo_t" - see the
592 short discussion of SELinux below.
595 Note, the context here is the target context when requesting a name,
596 NOT the context of the connection owning the name.
599 There's currently no way to set a default for owning any name, if
600 we add this syntax it will look like:
602 <associate own="*" context="foo_t"/>
604 If you find a reason this is useful, let the developers know.
605 Right now the default will be the security context of the bus itself.
608 If two <associate> elements specify the same name, the element
609 appearing later in the configuration file will be used.
614 See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:
617 Every subject (process) and object (e.g. file, socket, IPC object,
618 etc) in the system is assigned a collection of security attributes,
619 known as a security context. A security context contains all of the
620 security attributes associated with a particular subject or object
621 that are relevant to the security policy.
624 In order to better encapsulate security contexts and to provide
625 greater efficiency, the policy enforcement code of SELinux typically
626 handles security identifiers (SIDs) rather than security contexts. A
627 SID is an integer that is mapped by the security server to a security
631 When a security decision is required, the policy enforcement code
632 passes a pair of SIDs (typically the SID of a subject and the SID of
633 an object, but sometimes a pair of subject SIDs or a pair of object
634 SIDs), and an object security class to the security server. The object
635 security class indicates the kind of object, e.g. a process, a regular
636 file, a directory, a TCP socket, etc.
639 Access decisions specify whether or not a permission is granted for a
640 given pair of SIDs and class. Each object class has a set of
641 associated permissions defined to control operations on objects with
645 D-Bus performs SELinux security checks in two places.
648 First, any time a message is routed from one connection to another
649 connection, the bus daemon will check permissions with the security context of
650 the first connection as source, security context of the second connection
651 as target, object class "dbus" and requested permission "send_msg".
654 If a security context is not available for a connection
655 (impossible when using UNIX domain sockets), then the target
656 context used is the context of the bus daemon itself.
657 There is currently no way to change this default, because we're
658 assuming that only UNIX domain sockets will be used to
659 connect to the systemwide bus. If this changes, we'll
660 probably add a way to set the default connection context.
663 Second, any time a connection asks to own a name,
664 the bus daemon will check permissions with the security
665 context of the connection as source, the security context specified
666 for the name in the config file as target, object
667 class "dbus" and requested permission "acquire_svc".
670 The security context for a bus name is specified with the
671 <associate> element described earlier in this document.
672 If a name has no security context associated in the
673 configuration file, the security context of the bus daemon
679 If you're trying to figure out where your messages are going or why
680 you aren't getting messages, there are several things you can try.
683 Remember that the system bus is heavily locked down and if you
684 haven't installed a security policy file to allow your message
685 through, it won't work. For the session bus, this is not a concern.
688 The simplest way to figure out what's happening on the bus is to run
689 the \fIdbus-monitor\fP program, which comes with the D-Bus
690 package. You can also send test messages with \fIdbus-send\fP. These
691 programs have their own man pages.
694 If you want to know what the daemon itself is doing, you might consider
695 running a separate copy of the daemon to test against. This will allow you
696 to put the daemon under a debugger, or run it with verbose output, without
697 messing up your real session and system daemons.
700 To run a separate test copy of the daemon, for example you might open a terminal
703 DBUS_VERBOSE=1 dbus-daemon --session --print-address
707 The test daemon address will be printed when the daemon starts. You will need
708 to copy-and-paste this address and use it as the value of the
709 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
710 you want to test. This will cause those applications to connect to your
711 test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.
714 DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
715 was compiled with verbose mode enabled. This is not recommended in
716 production builds due to performance impact. You may need to rebuild
717 D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
718 also affects the D-Bus library and thus applications using D-Bus; it may
719 be useful to see verbose output on both the client side and from the daemon.)
722 If you want to get fancy, you can create a custom bus
723 configuration for your test bus (see the session.conf and system.conf
724 files that define the two default configurations for example). This
725 would allow you to specify a different directory for .service files,
730 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
733 Please send bug reports to the D-Bus mailing list or bug tracker,
734 see http://www.freedesktop.org/software/dbus/