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 If present, the bus daemon keeps its original umask when forking.
221 This may be useful to avoid affecting the behavior of child processes.
227 Add an address that the bus should listen on. The
228 address is in the standard D-Bus format that contains
229 a transport name plus possible parameters/options.
232 Example: <listen>unix:path=/tmp/foo</listen>
235 Example: <listen>tcp:host=localhost,port=1234</listen>
238 If there are multiple <listen> elements, then the bus listens
239 on multiple addresses. The bus will pass its address to
240 started services or other interested parties with
241 the last address given in <listen> first. That is,
242 apps will try to connect to the last <listen> address first.
245 tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.
246 If a hostname resolves to multiple addresses, the server will bind
247 to all of them. The family=ipv4 or family=ipv6 options can be used
248 to force it to bind to a subset of addresses
251 Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen>
254 A special case is using a port number of zero (or omitting the port),
255 which means to choose an available port selected by the operating
256 system. The port number chosen can be obtained with the
257 --print-address command line parameter and will be present in other
258 cases where the server reports its own address, such as when
259 DBUS_SESSION_BUS_ADDRESS is set.
262 Example: <listen>tcp:host=localhost,port=0</listen>
265 tcp addresses also allow a bind=hostname option, which will override
266 the host option specifying what address to bind to, without changing
267 the address reported by the bus. The bind option can also take a
268 special name '*' to cause the bus to listen on all local address
269 (INADDR_ANY). The specified host should be a valid name of the local
270 machine or weird stuff will happen.
273 Example: <listen>tcp:host=localhost,bind=*,port=0</listen>
279 Lists permitted authorization mechanisms. If this element doesn't
280 exist, then all known mechanisms are allowed. If there are multiple
281 <auth> elements, all the listed mechanisms are allowed. The order in
282 which mechanisms are listed is not meaningful.
285 Example: <auth>EXTERNAL</auth>
288 Example: <auth>DBUS_COOKIE_SHA1</auth>
294 Adds a directory to scan for .service files. Directories are
295 scanned starting with the last to appear in the config file
296 (the first .service file found that provides a particular
297 service will be used).
300 Service files tell the bus how to automatically start a program.
301 They are primarily used with the per-user-session bus,
302 not the systemwide bus.
305 .I "<standard_session_servicedirs/>"
308 <standard_session_servicedirs/> is equivalent to specifying a series
309 of <servicedir/> elements for each of the data directories in the "XDG
310 Base Directory Specification" with the subdirectory "dbus-1/services",
311 so for example "/usr/share/dbus-1/services" would be among the
312 directories searched.
315 The "XDG Base Directory Specification" can be found at
316 http://freedesktop.org/wiki/Standards/basedir-spec if it hasn't moved,
317 otherwise try your favorite search engine.
320 The <standard_session_servicedirs/> option is only relevant to the
321 per-user-session bus daemon defined in
322 @EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
323 configuration file would probably be nonsense.
326 .I "<standard_system_servicedirs/>"
329 <standard_system_servicedirs/> specifies the standard system-wide
330 activation directories that should be searched for service files.
331 This option defaults to @EXPANDED_DATADIR@/dbus-1/system-services.
334 The <standard_system_servicedirs/> option is only relevant to the
335 per-system bus daemon defined in
336 @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
337 configuration file would probably be nonsense.
340 .I "<servicehelper/>"
343 <servicehelper/> specifies the setuid helper that is used to launch
344 system daemons with an alternate user. Typically this should be
345 the dbus-daemon-launch-helper executable in located in libexec.
348 The <servicehelper/> option is only relevant to the per-system bus daemon
349 defined in @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
350 configuration file would probably be nonsense.
356 <limit> establishes a resource limit. For example:
358 <limit name="max_message_size">64</limit>
359 <limit name="max_completed_connections">512</limit>
363 The name attribute is mandatory.
364 Available limit names are:
366 "max_incoming_bytes" : total size in bytes of messages
367 incoming from a single connection
368 "max_outgoing_bytes" : total size in bytes of messages
369 queued up for a single connection
370 "max_message_size" : max size of a single message in
372 "service_start_timeout" : milliseconds (thousandths) until
373 a started service has to connect
374 "auth_timeout" : milliseconds (thousandths) a
375 connection is given to
377 "max_completed_connections" : max number of authenticated connections
378 "max_incomplete_connections" : max number of unauthenticated
380 "max_connections_per_user" : max number of completed connections from
382 "max_pending_service_starts" : max number of service launches in
383 progress at the same time
384 "max_names_per_connection" : max number of names a single
386 "max_match_rules_per_connection": max number of match rules for a single
388 "max_replies_per_connection" : max number of pending method
389 replies per connection
390 (number of calls-in-progress)
391 "reply_timeout" : milliseconds (thousandths)
392 until a method call times out
396 The max incoming/outgoing queue sizes allow a new message to be queued
397 if one byte remains below the max. So you can in fact exceed the max
401 max_completed_connections divided by max_connections_per_user is the
402 number of users that can work together to denial-of-service all other users by using
403 up all connections on the systemwide bus.
406 Limits are normally only of interest on the systemwide bus, not the user session
413 The <policy> element defines a security policy to be applied to a particular
414 set of connections to the bus. A policy is made up of
415 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
416 they are analogous to a firewall in that they allow expected traffic
417 and prevent unexpected traffic.
420 The <policy> element has one of three attributes:
422 context="(default|mandatory)"
423 user="username or userid"
424 group="group name or gid"
429 Policies are applied to a connection as follows:
431 - all context="default" policies are applied
432 - all group="connection's user's group" policies are applied
434 - all user="connection's auth user" policies are applied
436 - all context="mandatory" policies are applied
440 Policies applied later will override those applied earlier,
441 when the policies overlap. Multiple policies with the same
442 user/group/context are applied in the order they appear
450 A <deny> element appears below a <policy> element and prohibits some
451 action. The <allow> element makes an exception to previous <deny>
452 statements, and works just like <deny> but with the inverse meaning.
455 The possible attributes of these elements are:
457 send_interface="interface_name"
458 send_member="method_or_signal_name"
459 send_error="error_name"
460 send_destination="name"
461 send_type="method_call" | "method_return" | "signal" | "error"
462 send_path="/path/name"
464 receive_interface="interface_name"
465 receive_member="method_or_signal_name"
466 receive_error="error_name"
467 receive_sender="name"
468 receive_type="method_call" | "method_return" | "signal" | "error"
469 receive_path="/path/name"
471 send_requested_reply="true" | "false"
472 receive_requested_reply="true" | "false"
474 eavesdrop="true" | "false"
484 <deny send_interface="org.freedesktop.System" send_member="Reboot"/>
485 <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
486 <deny own="org.freedesktop.System"/>
487 <deny send_destination="org.freedesktop.System"/>
488 <deny receive_sender="org.freedesktop.System"/>
490 <deny group="enemies"/>
494 The <deny> element's attributes determine whether the deny "matches" a
495 particular action. If it matches, the action is denied (unless later
496 rules in the config file allow it).
499 send_destination and receive_sender rules mean that messages may not be
500 sent to or received from the *owner* of the given name, not that
501 they may not be sent *to that name*. That is, if a connection
502 owns services A, B, C, and sending to A is denied, sending to B or C
503 will not work either.
506 The other send_* and receive_* attributes are purely textual/by-value
507 matches against the given field in the message header.
510 "Eavesdropping" occurs when an application receives a message that
511 was explicitly addressed to a name the application does not own, or
512 is a reply to such a message. Eavesdropping thus only applies to
513 messages that are addressed to services and replies to such messages
514 (i.e. it does not apply to signals).
517 For <allow>, eavesdrop="true" indicates that the rule matches even
518 when eavesdropping. eavesdrop="false" is the default and means that
519 the rule only allows messages to go to their specified recipient.
520 For <deny>, eavesdrop="true" indicates that the rule matches
521 only when eavesdropping. eavesdrop="false" is the default for <deny>
522 also, but here it means that the rule applies always, even when
523 not eavesdropping. The eavesdrop attribute can only be combined with
524 send and receive rules (with send_* and receive_* attributes).
528 The [send|receive]_requested_reply attribute works similarly to the eavesdrop
529 attribute. It controls whether the <deny> or <allow> matches a reply
530 that is expected (corresponds to a previous method call message).
531 This attribute only makes sense for reply messages (errors and method
532 returns), and is ignored for other message types.
535 For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
536 only requested replies are allowed by the
537 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
541 For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
542 the rule matches only when the reply was not
543 requested. [send|receive]_requested_reply="true" indicates that the rule applies
544 always, regardless of pending reply state.
547 user and group denials mean that the given user or group may
548 not connect to the message bus.
551 For "name", "username", "groupname", etc.
552 the character "*" can be substituted, meaning "any." Complex globs
553 like "foo.bar.*" aren't allowed for now because they'd be work to
554 implement and maybe encourage sloppy security anyway.
557 It does not make sense to deny a user or group inside a <policy>
558 for a user or group; user/group denials can only be inside
559 context="default" or context="mandatory" policies.
562 A single <deny> rule may specify combinations of attributes such as
563 send_destination and send_interface and send_type. In this case, the
564 denial applies only if both attributes match the message being denied.
565 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
566 deny messages with the given interface AND the given bus name.
567 To get an OR effect you specify multiple <deny> rules.
570 You can't include both send_ and receive_ attributes on the same
571 rule, since "whether the message can be sent" and "whether it can be
572 received" are evaluated separately.
575 Be careful with send_interface/receive_interface, because the
576 interface field in messages is optional.
582 The <selinux> element contains settings related to Security Enhanced Linux.
589 An <associate> element appears below an <selinux> element and
590 creates a mapping. Right now only one kind of association is possible:
592 <associate own="org.freedesktop.Foobar" context="foo_t"/>
596 This means that if a connection asks to own the name
597 "org.freedesktop.Foobar" then the source context will be the context
598 of the connection and the target context will be "foo_t" - see the
599 short discussion of SELinux below.
602 Note, the context here is the target context when requesting a name,
603 NOT the context of the connection owning the name.
606 There's currently no way to set a default for owning any name, if
607 we add this syntax it will look like:
609 <associate own="*" context="foo_t"/>
611 If you find a reason this is useful, let the developers know.
612 Right now the default will be the security context of the bus itself.
615 If two <associate> elements specify the same name, the element
616 appearing later in the configuration file will be used.
621 See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:
624 Every subject (process) and object (e.g. file, socket, IPC object,
625 etc) in the system is assigned a collection of security attributes,
626 known as a security context. A security context contains all of the
627 security attributes associated with a particular subject or object
628 that are relevant to the security policy.
631 In order to better encapsulate security contexts and to provide
632 greater efficiency, the policy enforcement code of SELinux typically
633 handles security identifiers (SIDs) rather than security contexts. A
634 SID is an integer that is mapped by the security server to a security
638 When a security decision is required, the policy enforcement code
639 passes a pair of SIDs (typically the SID of a subject and the SID of
640 an object, but sometimes a pair of subject SIDs or a pair of object
641 SIDs), and an object security class to the security server. The object
642 security class indicates the kind of object, e.g. a process, a regular
643 file, a directory, a TCP socket, etc.
646 Access decisions specify whether or not a permission is granted for a
647 given pair of SIDs and class. Each object class has a set of
648 associated permissions defined to control operations on objects with
652 D-Bus performs SELinux security checks in two places.
655 First, any time a message is routed from one connection to another
656 connection, the bus daemon will check permissions with the security context of
657 the first connection as source, security context of the second connection
658 as target, object class "dbus" and requested permission "send_msg".
661 If a security context is not available for a connection
662 (impossible when using UNIX domain sockets), then the target
663 context used is the context of the bus daemon itself.
664 There is currently no way to change this default, because we're
665 assuming that only UNIX domain sockets will be used to
666 connect to the systemwide bus. If this changes, we'll
667 probably add a way to set the default connection context.
670 Second, any time a connection asks to own a name,
671 the bus daemon will check permissions with the security
672 context of the connection as source, the security context specified
673 for the name in the config file as target, object
674 class "dbus" and requested permission "acquire_svc".
677 The security context for a bus name is specified with the
678 <associate> element described earlier in this document.
679 If a name has no security context associated in the
680 configuration file, the security context of the bus daemon
686 If you're trying to figure out where your messages are going or why
687 you aren't getting messages, there are several things you can try.
690 Remember that the system bus is heavily locked down and if you
691 haven't installed a security policy file to allow your message
692 through, it won't work. For the session bus, this is not a concern.
695 The simplest way to figure out what's happening on the bus is to run
696 the \fIdbus-monitor\fP program, which comes with the D-Bus
697 package. You can also send test messages with \fIdbus-send\fP. These
698 programs have their own man pages.
701 If you want to know what the daemon itself is doing, you might consider
702 running a separate copy of the daemon to test against. This will allow you
703 to put the daemon under a debugger, or run it with verbose output, without
704 messing up your real session and system daemons.
707 To run a separate test copy of the daemon, for example you might open a terminal
710 DBUS_VERBOSE=1 dbus-daemon --session --print-address
714 The test daemon address will be printed when the daemon starts. You will need
715 to copy-and-paste this address and use it as the value of the
716 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
717 you want to test. This will cause those applications to connect to your
718 test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.
721 DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
722 was compiled with verbose mode enabled. This is not recommended in
723 production builds due to performance impact. You may need to rebuild
724 D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
725 also affects the D-Bus library and thus applications using D-Bus; it may
726 be useful to see verbose output on both the client side and from the daemon.)
729 If you want to get fancy, you can create a custom bus
730 configuration for your test bus (see the session.conf and system.conf
731 files that define the two default configurations for example). This
732 would allow you to specify a different directory for .service files,
737 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
740 Please send bug reports to the D-Bus mailing list or bug tracker,
741 see http://www.freedesktop.org/software/dbus/