2 .\" dbus-daemon-1 manual page.
3 .\" Copyright (C) 2003 Red Hat, Inc.
7 dbus-daemon-1 \- Message bus daemon
11 dbus-daemon-1 [\-\-version] [\-\-session] [\-\-system] [\-\-config-file=FILE]
12 [\-\-print-address[=DESCRIPTOR]] [\-\-print-pid[=DESCRIPTOR]] [\-\-fork]
16 \fIdbus-daemon-1\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-1\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" service) and the
27 per-user-login-session message bus (started each time a user logs in).
28 \fIdbus-daemon-1\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 There is no way to cause the D-BUS daemon to reload its configuration
54 file (HUP will not do so). The reason is that changing configuration
55 would break the semantics expected by applications connected to the
56 message bus. Thus, changing configuration would require kicking all
57 apps off the bus; so you may as well just restart the daemon.
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 If there are multiple <listen> elements, then the bus listens
215 on multiple addresses. The bus will pass its address to
216 activated services or other interested parties with
217 the last address given in <listen> first. That is,
218 apps will try to connect to the last <listen> address first.
224 Lists permitted authorization mechanisms. If this element doesn't
225 exist, then all known mechanisms are allowed. If there are multiple
226 <auth> elements, all the listed mechanisms are allowed. The order in
227 which mechanisms are listed is not meaningful.
230 Example: <auth>EXTERNAL</auth>
233 Example: <auth>DBUS_COOKIE_SHA1</auth>
239 Adds a directory to scan for .service files. Directories are
240 scanned starting with the last to appear in the config file
241 (the first .service file found that provides a particular
242 service will be used).
245 Service files tell the bus how to automatically start a particular
246 service. They are primarily used with the per-user-session bus,
247 not the systemwide bus.
253 <limit> establishes a resource limit. For example:
255 <limit name="max_message_size">64</limit>
256 <limit name="max_completed_connections">512</limit>
260 The name attribute is mandatory.
261 Available limit names are:
263 "max_incoming_bytes" : total size in bytes of messages
264 incoming from a single connection
265 "max_outgoing_bytes" : total size in bytes of messages
266 queued up for a single connection
267 "max_message_size" : max size of a single message in
269 "activation_timeout" : milliseconds (thousandths) until
270 an activated service has to connect
271 "auth_timeout" : milliseconds (thousandths) a
272 connection is given to
274 "max_completed_connections" : max number of authenticated connections
275 "max_incomplete_connections" : max number of unauthenticated
277 "max_connections_per_user" : max number of completed connections from
279 "max_pending_activations" : max number of activations in
280 progress at the same time
281 "max_services_per_connection": max number of services a single
283 "max_replies_per_connection" : max number of pending method
284 replies per connection
285 (number of calls-in-progress)
286 "reply_timeout" : milliseconds (thousandths)
287 until a method call times out
291 The max incoming/outgoing queue sizes allow a new message to be queued
292 if one byte remains below the max. So you can in fact exceed the max
296 max_completed_connections divided by max_connections_per_user is the
297 number of users that can work together to DOS all other users by using
304 The <policy> element defines a policy to be applied to a particular
305 set of connections to the bus. A policy is made up of
306 <allow> and <deny> elements.
309 The <policy> element has one of three attributes:
311 context="(default|mandatory)"
312 user="username or userid"
313 group="group name or gid"
318 Policies are applied to a connection as follows:
320 - all context="default" policies are applied
321 - all group="connection's user's group" policies are applied
323 - all user="connection's auth user" policies are applied
325 - all context="mandatory" policies are applied
329 Policies applied later will override those applied earlier,
330 when the policies overlap. Multiple policies with the same
331 user/group/context are applied in the order they appear
339 A <deny> element appears below a <policy> element and prohibits some
340 action. The <allow> element makes an exception to previous <deny>
341 statements, and works just like <deny> but with the inverse meaning.
344 The possible attributes of these elements are:
346 send_interface="interface_name"
347 send_member="method_or_signal_name"
348 send_error="error_name"
349 send_destination="service_name"
350 send_type="method_call" | "method_return" | "signal" | "error"
351 send_path="/path/name"
353 receive_interface="interface_name"
354 receive_member="method_or_signal_name"
355 receive_error="error_name"
356 receive_sender="service_name"
357 receive_type="method_call" | "method_return" | "signal" | "error"
358 receive_path="/path/name"
360 send_requested_reply="true" | "false"
361 receive_requested_reply="true" | "false"
363 eavesdrop="true" | "false"
373 <deny send_interface="org.freedesktop.System" send_member="Reboot"/>
374 <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
375 <deny own="org.freedesktop.System"/>
376 <deny send_destination="org.freedesktop.System"/>
377 <deny receive_sender="org.freedesktop.System"/>
379 <deny group="enemies"/>
383 The <deny> element's attributes determine whether the deny "matches" a
384 particular action. If it matches, the action is denied (unless later
385 rules in the config file allow it).
388 send_destination and receive_sender rules mean that messages may not be
389 sent to or received from the *owner* of the given service, not that
390 they may not be sent *to that service name*. That is, if a connection
391 owns services A, B, C, and sending to A is denied, sending to B or C
392 will not work either.
395 The other send_* and receive_* attributes are purely textual/by-value
396 matches against the given field in the message header.
399 "Eavesdropping" occurs when an application receives a message that
400 was explicitly addressed to a service the application does not own.
401 Eavesdropping thus only applies to messages that are addressed to
402 services (i.e. it does not apply to signals).
405 For <allow>, eavesdrop="true" indicates that the rule matches even
406 when eavesdropping. eavesdrop="false" is the default and means that
407 the rule only allows messages to go to their specified recipient.
408 For <deny>, eavesdrop="true" indicates that the rule matches
409 only when eavesdropping. eavesdrop="false" is the default for <deny>
410 also, but here it means that the rule applies always, even when
411 not eavesdropping. The eavesdrop attribute can only be combined with
412 receive rules (with receive_* attributes).
416 The [send|receive]_requested_reply attribute works similarly to the eavesdrop
417 attribute. It controls whether the <deny> or <allow> matches a reply
418 that is expected (corresponds to a previous method call message).
419 This attribute only makes sense for reply messages (errors and method
420 returns), and is ignored for other message types.
423 For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
424 only requested replies are allowed by the
425 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
429 For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
430 the rule matches only when the reply was not
431 requested. [send|receive]_requested_reply="true" indicates that the rule applies
432 always, regardless of pending reply state.
435 user and group denials mean that the given user or group may
436 not connect to the message bus.
439 For "service_name", "username", "groupname", etc.
440 the character "*" can be substituted, meaning "any." Complex globs
441 like "foo.bar.*" aren't allowed for now because they'd be work to
442 implement and maybe encourage sloppy security anyway.
445 It does not make sense to deny a user or group inside a <policy>
446 for a user or group; user/group denials can only be inside
447 context="default" or context="mandatory" policies.
450 A single <deny> rule may specify combinations of attributes such as
451 send_service and send_interface and send_type. In this case, the
452 denial applies only if both attributes match the message being denied.
453 e.g. <deny send_interface="foo.bar" send_service="foo.blah"/> would
454 deny messages of the given interface AND to the given service.
455 To get an OR effect you specify multiple <deny> rules.
458 You can't include both send_ and receive_ attributes on the same
459 rule, since "whether the message can be sent" and "whether it can be
460 received" are evaluated separately.
463 Be careful with send_interface/receive_interface, because the
464 interface field in messages is optional.
470 The <selinux> element contains settings related to Security Enhanced Linux.
477 An <associate> element appears below an <selinux> element and
478 creates a mapping. Right now only one kind of association is possible:
480 <associate own="org.freedesktop.Foobar" context="foo_t"/>
484 This means that if a connection asks to own the service
485 "org.freedesktop.Foobar" then the source context will be the context
486 of the connection and the target context will be "foo_t" - see the
487 short discussion of SELinux below.
490 Note, the context here is the target context when acquiring a service,
491 NOT the context of the connection owning the service.
494 There's currently no way to set a default for owning any service, if
495 we add this syntax it will look like:
497 <associate own="*" context="foo_t"/>
499 If you find a reason this is useful, let the developers know.
500 Right now the default will be the security context of the bus itself.
503 If two <associate> elements specify the same service name,
504 the element appearing later in the configuration file will
510 See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:
513 Every subject (process) and object (e.g. file, socket, IPC object,
514 etc) in the system is assigned a collection of security attributes,
515 known as a security context. A security context contains all of the
516 security attributes associated with a particular subject or object
517 that are relevant to the security policy.
520 In order to better encapsulate security contexts and to provide
521 greater efficiency, the policy enforcement code of SELinux typically
522 handles security identifiers (SIDs) rather than security contexts. A
523 SID is an integer that is mapped by the security server to a security
527 When a security decision is required, the policy enforcement code
528 passes a pair of SIDs (typically the SID of a subject and the SID of
529 an object, but sometimes a pair of subject SIDs or a pair of object
530 SIDs), and an object security class to the security server. The object
531 security class indicates the kind of object, e.g. a process, a regular
532 file, a directory, a TCP socket, etc.
535 Access decisions specify whether or not a permission is granted for a
536 given pair of SIDs and class. Each object class has a set of
537 associated permissions defined to control operations on objects with
541 D-BUS performs SELinux security checks in two places.
544 First, any time a message is routed from one connection to another
545 connection, the bus daemon will check permissions with the security context of
546 the first connection as source, security context of the second connection
547 as target, object class "dbus" and requested permission "send_msg".
550 If a security context is not available for a connection
551 (impossible when using UNIX domain sockets), then the target
552 context used is the context of the bus daemon itself.
553 There is currently no way to change this default, because we're
554 assuming that only UNIX domain sockets will be used to
555 connect to the systemwide bus. If this changes, we'll
556 probably add a way to set the default connection context.
559 Second, any time a connection asks to own a service,
560 the bus daemon will check permissions with the security
561 context of the connection as source, the security context specified
562 for the service name with an <associate> element as target, object
563 class "dbus" and requested permission "acquire_svc".
566 If the service name has no security context associated in the
567 configuration file, the security context of the bus daemon
571 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
574 Please send bug reports to the D-BUS mailing list or bug tracker,
575 see http://www.freedesktop.org/software/dbus/
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