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 A special case is using a port number of zero which means to
225 pick up a random free port. The real used port number could be retrieved
226 by using the --print-address command line parameter.
229 Example: <listen>tcp:host=localhost,port=0</listen>
235 Lists permitted authorization mechanisms. If this element doesn't
236 exist, then all known mechanisms are allowed. If there are multiple
237 <auth> elements, all the listed mechanisms are allowed. The order in
238 which mechanisms are listed is not meaningful.
241 Example: <auth>EXTERNAL</auth>
244 Example: <auth>DBUS_COOKIE_SHA1</auth>
250 Adds a directory to scan for .service files. Directories are
251 scanned starting with the last to appear in the config file
252 (the first .service file found that provides a particular
253 service will be used).
256 Service files tell the bus how to automatically start a program.
257 They are primarily used with the per-user-session bus,
258 not the systemwide bus.
261 .I "<standard_session_servicedirs/>"
264 <standard_session_servicedirs/> is equivalent to specifying a series
265 of <servicedir/> elements for each of the data directories in the "XDG
266 Base Directory Specification" with the subdirectory "dbus-1/services",
267 so for example "/usr/share/dbus-1/services" would be among the
268 directories searched.
271 The "XDG Base Directory Specification" can be found at
272 http://freedesktop.org/wiki/Standards/basedir-spec if it hasn't moved,
273 otherwise try your favorite search engine.
276 The <standard_session_servicedirs/> option is only relevant to the
277 per-user-session bus daemon defined in
278 @EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
279 configuration file would probably be nonsense.
285 <limit> establishes a resource limit. For example:
287 <limit name="max_message_size">64</limit>
288 <limit name="max_completed_connections">512</limit>
292 The name attribute is mandatory.
293 Available limit names are:
295 "max_incoming_bytes" : total size in bytes of messages
296 incoming from a single connection
297 "max_outgoing_bytes" : total size in bytes of messages
298 queued up for a single connection
299 "max_message_size" : max size of a single message in
301 "service_start_timeout" : milliseconds (thousandths) until
302 a started service has to connect
303 "auth_timeout" : milliseconds (thousandths) a
304 connection is given to
306 "max_completed_connections" : max number of authenticated connections
307 "max_incomplete_connections" : max number of unauthenticated
309 "max_connections_per_user" : max number of completed connections from
311 "max_pending_service_starts" : max number of service launches in
312 progress at the same time
313 "max_names_per_connection" : max number of names a single
315 "max_match_rules_per_connection": max number of match rules for a single
317 "max_replies_per_connection" : max number of pending method
318 replies per connection
319 (number of calls-in-progress)
320 "reply_timeout" : milliseconds (thousandths)
321 until a method call times out
325 The max incoming/outgoing queue sizes allow a new message to be queued
326 if one byte remains below the max. So you can in fact exceed the max
330 max_completed_connections divided by max_connections_per_user is the
331 number of users that can work together to denial-of-service all other users by using
332 up all connections on the systemwide bus.
335 Limits are normally only of interest on the systemwide bus, not the user session
342 The <policy> element defines a security policy to be applied to a particular
343 set of connections to the bus. A policy is made up of
344 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
345 they are analogous to a firewall in that they allow expected traffic
346 and prevent unexpected traffic.
349 The <policy> element has one of three attributes:
351 context="(default|mandatory)"
352 user="username or userid"
353 group="group name or gid"
358 Policies are applied to a connection as follows:
360 - all context="default" policies are applied
361 - all group="connection's user's group" policies are applied
363 - all user="connection's auth user" policies are applied
365 - all context="mandatory" policies are applied
369 Policies applied later will override those applied earlier,
370 when the policies overlap. Multiple policies with the same
371 user/group/context are applied in the order they appear
379 A <deny> element appears below a <policy> element and prohibits some
380 action. The <allow> element makes an exception to previous <deny>
381 statements, and works just like <deny> but with the inverse meaning.
384 The possible attributes of these elements are:
386 send_interface="interface_name"
387 send_member="method_or_signal_name"
388 send_error="error_name"
389 send_destination="name"
390 send_type="method_call" | "method_return" | "signal" | "error"
391 send_path="/path/name"
393 receive_interface="interface_name"
394 receive_member="method_or_signal_name"
395 receive_error="error_name"
396 receive_sender="name"
397 receive_type="method_call" | "method_return" | "signal" | "error"
398 receive_path="/path/name"
400 send_requested_reply="true" | "false"
401 receive_requested_reply="true" | "false"
403 eavesdrop="true" | "false"
413 <deny send_interface="org.freedesktop.System" send_member="Reboot"/>
414 <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
415 <deny own="org.freedesktop.System"/>
416 <deny send_destination="org.freedesktop.System"/>
417 <deny receive_sender="org.freedesktop.System"/>
419 <deny group="enemies"/>
423 The <deny> element's attributes determine whether the deny "matches" a
424 particular action. If it matches, the action is denied (unless later
425 rules in the config file allow it).
428 send_destination and receive_sender rules mean that messages may not be
429 sent to or received from the *owner* of the given name, not that
430 they may not be sent *to that name*. That is, if a connection
431 owns services A, B, C, and sending to A is denied, sending to B or C
432 will not work either.
435 The other send_* and receive_* attributes are purely textual/by-value
436 matches against the given field in the message header.
439 "Eavesdropping" occurs when an application receives a message that
440 was explicitly addressed to a name the application does not own.
441 Eavesdropping thus only applies to messages that are addressed to
442 services (i.e. it does not apply to signals).
445 For <allow>, eavesdrop="true" indicates that the rule matches even
446 when eavesdropping. eavesdrop="false" is the default and means that
447 the rule only allows messages to go to their specified recipient.
448 For <deny>, eavesdrop="true" indicates that the rule matches
449 only when eavesdropping. eavesdrop="false" is the default for <deny>
450 also, but here it means that the rule applies always, even when
451 not eavesdropping. The eavesdrop attribute can only be combined with
452 receive rules (with receive_* attributes).
456 The [send|receive]_requested_reply attribute works similarly to the eavesdrop
457 attribute. It controls whether the <deny> or <allow> matches a reply
458 that is expected (corresponds to a previous method call message).
459 This attribute only makes sense for reply messages (errors and method
460 returns), and is ignored for other message types.
463 For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
464 only requested replies are allowed by the
465 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
469 For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
470 the rule matches only when the reply was not
471 requested. [send|receive]_requested_reply="true" indicates that the rule applies
472 always, regardless of pending reply state.
475 user and group denials mean that the given user or group may
476 not connect to the message bus.
479 For "name", "username", "groupname", etc.
480 the character "*" can be substituted, meaning "any." Complex globs
481 like "foo.bar.*" aren't allowed for now because they'd be work to
482 implement and maybe encourage sloppy security anyway.
485 It does not make sense to deny a user or group inside a <policy>
486 for a user or group; user/group denials can only be inside
487 context="default" or context="mandatory" policies.
490 A single <deny> rule may specify combinations of attributes such as
491 send_destination and send_interface and send_type. In this case, the
492 denial applies only if both attributes match the message being denied.
493 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
494 deny messages with the given interface AND the given bus name.
495 To get an OR effect you specify multiple <deny> rules.
498 You can't include both send_ and receive_ attributes on the same
499 rule, since "whether the message can be sent" and "whether it can be
500 received" are evaluated separately.
503 Be careful with send_interface/receive_interface, because the
504 interface field in messages is optional.
510 The <selinux> element contains settings related to Security Enhanced Linux.
517 An <associate> element appears below an <selinux> element and
518 creates a mapping. Right now only one kind of association is possible:
520 <associate own="org.freedesktop.Foobar" context="foo_t"/>
524 This means that if a connection asks to own the name
525 "org.freedesktop.Foobar" then the source context will be the context
526 of the connection and the target context will be "foo_t" - see the
527 short discussion of SELinux below.
530 Note, the context here is the target context when requesting a name,
531 NOT the context of the connection owning the name.
534 There's currently no way to set a default for owning any name, if
535 we add this syntax it will look like:
537 <associate own="*" context="foo_t"/>
539 If you find a reason this is useful, let the developers know.
540 Right now the default will be the security context of the bus itself.
543 If two <associate> elements specify the same name, the element
544 appearing later in the configuration file will be used.
549 See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:
552 Every subject (process) and object (e.g. file, socket, IPC object,
553 etc) in the system is assigned a collection of security attributes,
554 known as a security context. A security context contains all of the
555 security attributes associated with a particular subject or object
556 that are relevant to the security policy.
559 In order to better encapsulate security contexts and to provide
560 greater efficiency, the policy enforcement code of SELinux typically
561 handles security identifiers (SIDs) rather than security contexts. A
562 SID is an integer that is mapped by the security server to a security
566 When a security decision is required, the policy enforcement code
567 passes a pair of SIDs (typically the SID of a subject and the SID of
568 an object, but sometimes a pair of subject SIDs or a pair of object
569 SIDs), and an object security class to the security server. The object
570 security class indicates the kind of object, e.g. a process, a regular
571 file, a directory, a TCP socket, etc.
574 Access decisions specify whether or not a permission is granted for a
575 given pair of SIDs and class. Each object class has a set of
576 associated permissions defined to control operations on objects with
580 D-Bus performs SELinux security checks in two places.
583 First, any time a message is routed from one connection to another
584 connection, the bus daemon will check permissions with the security context of
585 the first connection as source, security context of the second connection
586 as target, object class "dbus" and requested permission "send_msg".
589 If a security context is not available for a connection
590 (impossible when using UNIX domain sockets), then the target
591 context used is the context of the bus daemon itself.
592 There is currently no way to change this default, because we're
593 assuming that only UNIX domain sockets will be used to
594 connect to the systemwide bus. If this changes, we'll
595 probably add a way to set the default connection context.
598 Second, any time a connection asks to own a name,
599 the bus daemon will check permissions with the security
600 context of the connection as source, the security context specified
601 for the name in the config file as target, object
602 class "dbus" and requested permission "acquire_svc".
605 The security context for a bus name is specified with the
606 <associate> element described earlier in this document.
607 If a name has no security context associated in the
608 configuration file, the security context of the bus daemon
614 If you're trying to figure out where your messages are going or why
615 you aren't getting messages, there are several things you can try.
618 Remember that the system bus is heavily locked down and if you
619 haven't installed a security policy file to allow your message
620 through, it won't work. For the session bus, this is not a concern.
623 The simplest way to figure out what's happening on the bus is to run
624 the \fIdbus-monitor\fP program, which comes with the D-Bus
625 package. You can also send test messages with \fIdbus-send\fP. These
626 programs have their own man pages.
629 If you want to know what the daemon itself is doing, you might consider
630 running a separate copy of the daemon to test against. This will allow you
631 to put the daemon under a debugger, or run it with verbose output, without
632 messing up your real session and system daemons.
635 To run a separate test copy of the daemon, for example you might open a terminal
638 DBUS_VERBOSE=1 dbus-daemon --session --print-address
642 The test daemon address will be printed when the daemon starts. You will need
643 to copy-and-paste this address and use it as the value of the
644 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
645 you want to test. This will cause those applications to connect to your
646 test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.
649 DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
650 was compiled with verbose mode enabled. This is not recommended in
651 production builds due to performance impact. You may need to rebuild
652 D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
653 also affects the D-Bus library and thus applications using D-Bus; it may
654 be useful to see verbose output on both the client side and from the daemon.)
657 If you want to get fancy, you can create a custom bus
658 configuration for your test bus (see the session.conf and system.conf
659 files that define the two default configurations for example). This
660 would allow you to specify a different directory for .service files,
665 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
668 Please send bug reports to the D-Bus mailing list or bug tracker,
669 see http://www.freedesktop.org/software/dbus/