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).
144 Example: <type>session</type>
150 Include a file <include>filename.conf</include> at this point. If the
151 filename is relative, it is located relative to the configuration file
155 <include> has an optional attribute "ignore_missing=(yes|no)"
156 which defaults to "no" if not provided. This attribute
157 controls whether it's a fatal error for the included file
164 Include all files in <includedir>foo.d</includedir> at this
165 point. Files in the directory are included in undefined order.
166 Only files ending in ".conf" are included.
169 This is intended to allow extension of the system bus by particular
170 packages. For example, if CUPS wants to be able to send out
171 notification of printer queue changes, it could install a file to
172 @EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
173 this message and allowed the printer daemon user to send it.
179 The user account the daemon should run as, as either a username or a
180 UID. If the daemon cannot change to this UID on startup, it will exit.
181 If this element is not present, the daemon will not change or care
185 The last <user> entry in the file "wins", the others are ignored.
188 The user is changed after the bus has completed initialization. So
189 sockets etc. will be created before changing user, but no data will be
190 read from clients before changing user. This means that sockets
191 and PID files can be created in a location that requires root
192 privileges for writing.
198 If present, the bus daemon becomes a real daemon (forks
199 into the background, etc.). This is generally used
200 rather than the \-\-fork command line option.
206 Add an address that the bus should listen on. The
207 address is in the standard D-Bus format that contains
208 a transport name plus possible parameters/options.
211 Example: <listen>unix:path=/tmp/foo</listen>
214 Example: <listen>tcp:host=localhost,port=1234</listen>
217 If there are multiple <listen> elements, then the bus listens
218 on multiple addresses. The bus will pass its address to
219 started services or other interested parties with
220 the last address given in <listen> first. That is,
221 apps will try to connect to the last <listen> address first.
224 tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.
225 If a hostname resolves to multiple addresses, the server will bind
226 to all of them. The family=ipv4 or family=ipv6 options can be used
227 to force it to bind to a subset of addresses
230 Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen>
233 A special case is using a port number of zero (or omitting the port),
234 which means to choose an available port selected by the operating
235 system. The port number chosen can be obtained with the
236 --print-address command line parameter and will be present in other
237 cases where the server reports its own address, such as when
238 DBUS_SESSION_BUS_ADDRESS is set.
241 Example: <listen>tcp:host=localhost,port=0</listen>
244 tcp addresses also allow a bind=hostname option, which will override
245 the host option specifying what address to bind to, without changing
246 the address reported by the bus. The bind option can also take a
247 special name '*' to cause the bus to listen on all local address
248 (INADDR_ANY). The specified host should be a valid name of the local
249 machine or weird stuff will happen.
252 Example: <listen>tcp:host=localhost,bind=*,port=0</listen>
258 Lists permitted authorization mechanisms. If this element doesn't
259 exist, then all known mechanisms are allowed. If there are multiple
260 <auth> elements, all the listed mechanisms are allowed. The order in
261 which mechanisms are listed is not meaningful.
264 Example: <auth>EXTERNAL</auth>
267 Example: <auth>DBUS_COOKIE_SHA1</auth>
273 Adds a directory to scan for .service files. Directories are
274 scanned starting with the last to appear in the config file
275 (the first .service file found that provides a particular
276 service will be used).
279 Service files tell the bus how to automatically start a program.
280 They are primarily used with the per-user-session bus,
281 not the systemwide bus.
284 .I "<standard_session_servicedirs/>"
287 <standard_session_servicedirs/> is equivalent to specifying a series
288 of <servicedir/> elements for each of the data directories in the "XDG
289 Base Directory Specification" with the subdirectory "dbus-1/services",
290 so for example "/usr/share/dbus-1/services" would be among the
291 directories searched.
294 The "XDG Base Directory Specification" can be found at
295 http://freedesktop.org/wiki/Standards/basedir-spec if it hasn't moved,
296 otherwise try your favorite search engine.
299 The <standard_session_servicedirs/> option is only relevant to the
300 per-user-session bus daemon defined in
301 @EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
302 configuration file would probably be nonsense.
305 .I "<standard_system_servicedirs/>"
308 <standard_system_servicedirs/> specifies the standard system-wide
309 activation directories that should be searched for service files.
310 This option defaults to @EXPANDED_DATADIR@/dbus-1/system-services.
313 The <standard_system_servicedirs/> option is only relevant to the
314 per-system bus daemon defined in
315 @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
316 configuration file would probably be nonsense.
319 .I "<servicehelper/>"
322 <servicehelper/> specifies the setuid helper that is used to launch
323 system daemons with an alternate user. Typically this should be
324 the dbus-daemon-launch-helper executable in located in libexec.
327 The <servicehelper/> option is only relevant to the per-system bus daemon
328 defined in @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
329 configuration file would probably be nonsense.
335 <limit> establishes a resource limit. For example:
337 <limit name="max_message_size">64</limit>
338 <limit name="max_completed_connections">512</limit>
342 The name attribute is mandatory.
343 Available limit names are:
345 "max_incoming_bytes" : total size in bytes of messages
346 incoming from a single connection
347 "max_outgoing_bytes" : total size in bytes of messages
348 queued up for a single connection
349 "max_message_size" : max size of a single message in
351 "service_start_timeout" : milliseconds (thousandths) until
352 a started service has to connect
353 "auth_timeout" : milliseconds (thousandths) a
354 connection is given to
356 "max_completed_connections" : max number of authenticated connections
357 "max_incomplete_connections" : max number of unauthenticated
359 "max_connections_per_user" : max number of completed connections from
361 "max_pending_service_starts" : max number of service launches in
362 progress at the same time
363 "max_names_per_connection" : max number of names a single
365 "max_match_rules_per_connection": max number of match rules for a single
367 "max_replies_per_connection" : max number of pending method
368 replies per connection
369 (number of calls-in-progress)
370 "reply_timeout" : milliseconds (thousandths)
371 until a method call times out
375 The max incoming/outgoing queue sizes allow a new message to be queued
376 if one byte remains below the max. So you can in fact exceed the max
380 max_completed_connections divided by max_connections_per_user is the
381 number of users that can work together to denial-of-service all other users by using
382 up all connections on the systemwide bus.
385 Limits are normally only of interest on the systemwide bus, not the user session
392 The <policy> element defines a security policy to be applied to a particular
393 set of connections to the bus. A policy is made up of
394 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
395 they are analogous to a firewall in that they allow expected traffic
396 and prevent unexpected traffic.
399 The <policy> element has one of three attributes:
401 context="(default|mandatory)"
402 user="username or userid"
403 group="group name or gid"
408 Policies are applied to a connection as follows:
410 - all context="default" policies are applied
411 - all group="connection's user's group" policies are applied
413 - all user="connection's auth user" policies are applied
415 - all context="mandatory" policies are applied
419 Policies applied later will override those applied earlier,
420 when the policies overlap. Multiple policies with the same
421 user/group/context are applied in the order they appear
429 A <deny> element appears below a <policy> element and prohibits some
430 action. The <allow> element makes an exception to previous <deny>
431 statements, and works just like <deny> but with the inverse meaning.
434 The possible attributes of these elements are:
436 send_interface="interface_name"
437 send_member="method_or_signal_name"
438 send_error="error_name"
439 send_destination="name"
440 send_type="method_call" | "method_return" | "signal" | "error"
441 send_path="/path/name"
443 receive_interface="interface_name"
444 receive_member="method_or_signal_name"
445 receive_error="error_name"
446 receive_sender="name"
447 receive_type="method_call" | "method_return" | "signal" | "error"
448 receive_path="/path/name"
450 send_requested_reply="true" | "false"
451 receive_requested_reply="true" | "false"
453 eavesdrop="true" | "false"
463 <deny send_interface="org.freedesktop.System" send_member="Reboot"/>
464 <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
465 <deny own="org.freedesktop.System"/>
466 <deny send_destination="org.freedesktop.System"/>
467 <deny receive_sender="org.freedesktop.System"/>
469 <deny group="enemies"/>
473 The <deny> element's attributes determine whether the deny "matches" a
474 particular action. If it matches, the action is denied (unless later
475 rules in the config file allow it).
478 send_destination and receive_sender rules mean that messages may not be
479 sent to or received from the *owner* of the given name, not that
480 they may not be sent *to that name*. That is, if a connection
481 owns services A, B, C, and sending to A is denied, sending to B or C
482 will not work either.
485 The other send_* and receive_* attributes are purely textual/by-value
486 matches against the given field in the message header.
489 "Eavesdropping" occurs when an application receives a message that
490 was explicitly addressed to a name the application does not own, or
491 is a reply to such a message. Eavesdropping thus only applies to
492 messages that are addressed to services and replies to such messages
493 (i.e. it does not apply to signals).
496 For <allow>, eavesdrop="true" indicates that the rule matches even
497 when eavesdropping. eavesdrop="false" is the default and means that
498 the rule only allows messages to go to their specified recipient.
499 For <deny>, eavesdrop="true" indicates that the rule matches
500 only when eavesdropping. eavesdrop="false" is the default for <deny>
501 also, but here it means that the rule applies always, even when
502 not eavesdropping. The eavesdrop attribute can only be combined with
503 send and receive rules (with send_* and receive_* attributes).
507 The [send|receive]_requested_reply attribute works similarly to the eavesdrop
508 attribute. It controls whether the <deny> or <allow> matches a reply
509 that is expected (corresponds to a previous method call message).
510 This attribute only makes sense for reply messages (errors and method
511 returns), and is ignored for other message types.
514 For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
515 only requested replies are allowed by the
516 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
520 For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
521 the rule matches only when the reply was not
522 requested. [send|receive]_requested_reply="true" indicates that the rule applies
523 always, regardless of pending reply state.
526 user and group denials mean that the given user or group may
527 not connect to the message bus.
530 For "name", "username", "groupname", etc.
531 the character "*" can be substituted, meaning "any." Complex globs
532 like "foo.bar.*" aren't allowed for now because they'd be work to
533 implement and maybe encourage sloppy security anyway.
536 It does not make sense to deny a user or group inside a <policy>
537 for a user or group; user/group denials can only be inside
538 context="default" or context="mandatory" policies.
541 A single <deny> rule may specify combinations of attributes such as
542 send_destination and send_interface and send_type. In this case, the
543 denial applies only if both attributes match the message being denied.
544 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
545 deny messages with the given interface AND the given bus name.
546 To get an OR effect you specify multiple <deny> rules.
549 You can't include both send_ and receive_ attributes on the same
550 rule, since "whether the message can be sent" and "whether it can be
551 received" are evaluated separately.
554 Be careful with send_interface/receive_interface, because the
555 interface field in messages is optional.
561 The <selinux> element contains settings related to Security Enhanced Linux.
568 An <associate> element appears below an <selinux> element and
569 creates a mapping. Right now only one kind of association is possible:
571 <associate own="org.freedesktop.Foobar" context="foo_t"/>
575 This means that if a connection asks to own the name
576 "org.freedesktop.Foobar" then the source context will be the context
577 of the connection and the target context will be "foo_t" - see the
578 short discussion of SELinux below.
581 Note, the context here is the target context when requesting a name,
582 NOT the context of the connection owning the name.
585 There's currently no way to set a default for owning any name, if
586 we add this syntax it will look like:
588 <associate own="*" context="foo_t"/>
590 If you find a reason this is useful, let the developers know.
591 Right now the default will be the security context of the bus itself.
594 If two <associate> elements specify the same name, the element
595 appearing later in the configuration file will be used.
600 See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:
603 Every subject (process) and object (e.g. file, socket, IPC object,
604 etc) in the system is assigned a collection of security attributes,
605 known as a security context. A security context contains all of the
606 security attributes associated with a particular subject or object
607 that are relevant to the security policy.
610 In order to better encapsulate security contexts and to provide
611 greater efficiency, the policy enforcement code of SELinux typically
612 handles security identifiers (SIDs) rather than security contexts. A
613 SID is an integer that is mapped by the security server to a security
617 When a security decision is required, the policy enforcement code
618 passes a pair of SIDs (typically the SID of a subject and the SID of
619 an object, but sometimes a pair of subject SIDs or a pair of object
620 SIDs), and an object security class to the security server. The object
621 security class indicates the kind of object, e.g. a process, a regular
622 file, a directory, a TCP socket, etc.
625 Access decisions specify whether or not a permission is granted for a
626 given pair of SIDs and class. Each object class has a set of
627 associated permissions defined to control operations on objects with
631 D-Bus performs SELinux security checks in two places.
634 First, any time a message is routed from one connection to another
635 connection, the bus daemon will check permissions with the security context of
636 the first connection as source, security context of the second connection
637 as target, object class "dbus" and requested permission "send_msg".
640 If a security context is not available for a connection
641 (impossible when using UNIX domain sockets), then the target
642 context used is the context of the bus daemon itself.
643 There is currently no way to change this default, because we're
644 assuming that only UNIX domain sockets will be used to
645 connect to the systemwide bus. If this changes, we'll
646 probably add a way to set the default connection context.
649 Second, any time a connection asks to own a name,
650 the bus daemon will check permissions with the security
651 context of the connection as source, the security context specified
652 for the name in the config file as target, object
653 class "dbus" and requested permission "acquire_svc".
656 The security context for a bus name is specified with the
657 <associate> element described earlier in this document.
658 If a name has no security context associated in the
659 configuration file, the security context of the bus daemon
665 If you're trying to figure out where your messages are going or why
666 you aren't getting messages, there are several things you can try.
669 Remember that the system bus is heavily locked down and if you
670 haven't installed a security policy file to allow your message
671 through, it won't work. For the session bus, this is not a concern.
674 The simplest way to figure out what's happening on the bus is to run
675 the \fIdbus-monitor\fP program, which comes with the D-Bus
676 package. You can also send test messages with \fIdbus-send\fP. These
677 programs have their own man pages.
680 If you want to know what the daemon itself is doing, you might consider
681 running a separate copy of the daemon to test against. This will allow you
682 to put the daemon under a debugger, or run it with verbose output, without
683 messing up your real session and system daemons.
686 To run a separate test copy of the daemon, for example you might open a terminal
689 DBUS_VERBOSE=1 dbus-daemon --session --print-address
693 The test daemon address will be printed when the daemon starts. You will need
694 to copy-and-paste this address and use it as the value of the
695 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
696 you want to test. This will cause those applications to connect to your
697 test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.
700 DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
701 was compiled with verbose mode enabled. This is not recommended in
702 production builds due to performance impact. You may need to rebuild
703 D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
704 also affects the D-Bus library and thus applications using D-Bus; it may
705 be useful to see verbose output on both the client side and from the daemon.)
708 If you want to get fancy, you can create a custom bus
709 configuration for your test bus (see the session.conf and system.conf
710 files that define the two default configurations for example). This
711 would allow you to specify a different directory for .service files,
716 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
719 Please send bug reports to the D-Bus mailing list or bug tracker,
720 see http://www.freedesktop.org/software/dbus/