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 If there are multiple <listen> elements, then the bus listens
215 on multiple addresses. The bus will pass its address to
216 started 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 program.
246 They are primarily used with the per-user-session bus,
247 not the systemwide bus.
250 .I "<standard_session_servicedirs/>"
253 <standard_session_servicedirs/> is equivalent to specifying a series
254 of <servicedir/> elements for each of the data directories in the "XDG
255 Base Directory Specification" with the subdirectory "dbus-1/services",
256 so for example "/usr/share/dbus-1/services" would be among the
257 directories searched.
260 The "XDG Base Directory Specification" can be found at
261 http://freedesktop.org/wiki/Standards/basedir-spec if it hasn't moved,
262 otherwise try your favorite search engine.
265 The <standard_session_servicedirs/> option is only relevant to the
266 per-user-session bus daemon defined in
267 @EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
268 configuration file would probably be nonsense.
274 <limit> establishes a resource limit. For example:
276 <limit name="max_message_size">64</limit>
277 <limit name="max_completed_connections">512</limit>
281 The name attribute is mandatory.
282 Available limit names are:
284 "max_incoming_bytes" : total size in bytes of messages
285 incoming from a single connection
286 "max_outgoing_bytes" : total size in bytes of messages
287 queued up for a single connection
288 "max_message_size" : max size of a single message in
290 "service_start_timeout" : milliseconds (thousandths) until
291 a started service has to connect
292 "auth_timeout" : milliseconds (thousandths) a
293 connection is given to
295 "max_completed_connections" : max number of authenticated connections
296 "max_incomplete_connections" : max number of unauthenticated
298 "max_connections_per_user" : max number of completed connections from
300 "max_pending_service_starts" : max number of service launches in
301 progress at the same time
302 "max_names_per_connection" : max number of names a single
304 "max_match_rules_per_connection": max number of match rules for a single
306 "max_replies_per_connection" : max number of pending method
307 replies per connection
308 (number of calls-in-progress)
309 "reply_timeout" : milliseconds (thousandths)
310 until a method call times out
314 The max incoming/outgoing queue sizes allow a new message to be queued
315 if one byte remains below the max. So you can in fact exceed the max
319 max_completed_connections divided by max_connections_per_user is the
320 number of users that can work together to denial-of-service all other users by using
321 up all connections on the systemwide bus.
324 Limits are normally only of interest on the systemwide bus, not the user session
331 The <policy> element defines a security policy to be applied to a particular
332 set of connections to the bus. A policy is made up of
333 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
334 they are analogous to a firewall in that they allow expected traffic
335 and prevent unexpected traffic.
338 The <policy> element has one of three attributes:
340 context="(default|mandatory)"
341 user="username or userid"
342 group="group name or gid"
347 Policies are applied to a connection as follows:
349 - all context="default" policies are applied
350 - all group="connection's user's group" policies are applied
352 - all user="connection's auth user" policies are applied
354 - all context="mandatory" policies are applied
358 Policies applied later will override those applied earlier,
359 when the policies overlap. Multiple policies with the same
360 user/group/context are applied in the order they appear
368 A <deny> element appears below a <policy> element and prohibits some
369 action. The <allow> element makes an exception to previous <deny>
370 statements, and works just like <deny> but with the inverse meaning.
373 The possible attributes of these elements are:
375 send_interface="interface_name"
376 send_member="method_or_signal_name"
377 send_error="error_name"
378 send_destination="name"
379 send_type="method_call" | "method_return" | "signal" | "error"
380 send_path="/path/name"
382 receive_interface="interface_name"
383 receive_member="method_or_signal_name"
384 receive_error="error_name"
385 receive_sender="name"
386 receive_type="method_call" | "method_return" | "signal" | "error"
387 receive_path="/path/name"
389 send_requested_reply="true" | "false"
390 receive_requested_reply="true" | "false"
392 eavesdrop="true" | "false"
402 <deny send_interface="org.freedesktop.System" send_member="Reboot"/>
403 <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
404 <deny own="org.freedesktop.System"/>
405 <deny send_destination="org.freedesktop.System"/>
406 <deny receive_sender="org.freedesktop.System"/>
408 <deny group="enemies"/>
412 The <deny> element's attributes determine whether the deny "matches" a
413 particular action. If it matches, the action is denied (unless later
414 rules in the config file allow it).
417 send_destination and receive_sender rules mean that messages may not be
418 sent to or received from the *owner* of the given name, not that
419 they may not be sent *to that name*. That is, if a connection
420 owns services A, B, C, and sending to A is denied, sending to B or C
421 will not work either.
424 The other send_* and receive_* attributes are purely textual/by-value
425 matches against the given field in the message header.
428 "Eavesdropping" occurs when an application receives a message that
429 was explicitly addressed to a name the application does not own.
430 Eavesdropping thus only applies to messages that are addressed to
431 services (i.e. it does not apply to signals).
434 For <allow>, eavesdrop="true" indicates that the rule matches even
435 when eavesdropping. eavesdrop="false" is the default and means that
436 the rule only allows messages to go to their specified recipient.
437 For <deny>, eavesdrop="true" indicates that the rule matches
438 only when eavesdropping. eavesdrop="false" is the default for <deny>
439 also, but here it means that the rule applies always, even when
440 not eavesdropping. The eavesdrop attribute can only be combined with
441 receive rules (with receive_* attributes).
445 The [send|receive]_requested_reply attribute works similarly to the eavesdrop
446 attribute. It controls whether the <deny> or <allow> matches a reply
447 that is expected (corresponds to a previous method call message).
448 This attribute only makes sense for reply messages (errors and method
449 returns), and is ignored for other message types.
452 For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
453 only requested replies are allowed by the
454 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
458 For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
459 the rule matches only when the reply was not
460 requested. [send|receive]_requested_reply="true" indicates that the rule applies
461 always, regardless of pending reply state.
464 user and group denials mean that the given user or group may
465 not connect to the message bus.
468 For "name", "username", "groupname", etc.
469 the character "*" can be substituted, meaning "any." Complex globs
470 like "foo.bar.*" aren't allowed for now because they'd be work to
471 implement and maybe encourage sloppy security anyway.
474 It does not make sense to deny a user or group inside a <policy>
475 for a user or group; user/group denials can only be inside
476 context="default" or context="mandatory" policies.
479 A single <deny> rule may specify combinations of attributes such as
480 send_destination and send_interface and send_type. In this case, the
481 denial applies only if both attributes match the message being denied.
482 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
483 deny messages with the given interface AND the given bus name.
484 To get an OR effect you specify multiple <deny> rules.
487 You can't include both send_ and receive_ attributes on the same
488 rule, since "whether the message can be sent" and "whether it can be
489 received" are evaluated separately.
492 Be careful with send_interface/receive_interface, because the
493 interface field in messages is optional.
499 The <selinux> element contains settings related to Security Enhanced Linux.
506 An <associate> element appears below an <selinux> element and
507 creates a mapping. Right now only one kind of association is possible:
509 <associate own="org.freedesktop.Foobar" context="foo_t"/>
513 This means that if a connection asks to own the name
514 "org.freedesktop.Foobar" then the source context will be the context
515 of the connection and the target context will be "foo_t" - see the
516 short discussion of SELinux below.
519 Note, the context here is the target context when requesting a name,
520 NOT the context of the connection owning the name.
523 There's currently no way to set a default for owning any name, if
524 we add this syntax it will look like:
526 <associate own="*" context="foo_t"/>
528 If you find a reason this is useful, let the developers know.
529 Right now the default will be the security context of the bus itself.
532 If two <associate> elements specify the same name, the element
533 appearing later in the configuration file will be used.
538 See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:
541 Every subject (process) and object (e.g. file, socket, IPC object,
542 etc) in the system is assigned a collection of security attributes,
543 known as a security context. A security context contains all of the
544 security attributes associated with a particular subject or object
545 that are relevant to the security policy.
548 In order to better encapsulate security contexts and to provide
549 greater efficiency, the policy enforcement code of SELinux typically
550 handles security identifiers (SIDs) rather than security contexts. A
551 SID is an integer that is mapped by the security server to a security
555 When a security decision is required, the policy enforcement code
556 passes a pair of SIDs (typically the SID of a subject and the SID of
557 an object, but sometimes a pair of subject SIDs or a pair of object
558 SIDs), and an object security class to the security server. The object
559 security class indicates the kind of object, e.g. a process, a regular
560 file, a directory, a TCP socket, etc.
563 Access decisions specify whether or not a permission is granted for a
564 given pair of SIDs and class. Each object class has a set of
565 associated permissions defined to control operations on objects with
569 D-Bus performs SELinux security checks in two places.
572 First, any time a message is routed from one connection to another
573 connection, the bus daemon will check permissions with the security context of
574 the first connection as source, security context of the second connection
575 as target, object class "dbus" and requested permission "send_msg".
578 If a security context is not available for a connection
579 (impossible when using UNIX domain sockets), then the target
580 context used is the context of the bus daemon itself.
581 There is currently no way to change this default, because we're
582 assuming that only UNIX domain sockets will be used to
583 connect to the systemwide bus. If this changes, we'll
584 probably add a way to set the default connection context.
587 Second, any time a connection asks to own a name,
588 the bus daemon will check permissions with the security
589 context of the connection as source, the security context specified
590 for the name in the config file as target, object
591 class "dbus" and requested permission "acquire_svc".
594 The security context for a bus name is specified with the
595 <associate> element described earlier in this document.
596 If a name has no security context associated in the
597 configuration file, the security context of the bus daemon
601 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
604 Please send bug reports to the D-Bus mailing list or bug tracker,
605 see http://www.freedesktop.org/software/dbus/