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. Some configuration changes would require kicking
55 all apps off the bus; so they will only take effect if you restart the
56 daemon. Policy changes should take effect with SIGHUP.
59 The following options are supported:
61 .I "--config-file=FILE"
62 Use the given configuration file.
65 Force the message bus to fork and become a daemon, even if
66 the configuration file does not specify that it should.
67 In most contexts the configuration file already gets this
70 .I "--print-address[=DESCRIPTOR]"
71 Print the address of the message bus to standard output, or
72 to the given file descriptor. This is used by programs that
73 launch the message bus.
75 .I "--print-pid[=DESCRIPTOR]"
76 Print the process ID of the message bus to standard output, or
77 to the given file descriptor. This is used by programs that
78 launch the message bus.
81 Use the standard configuration file for the per-login-session message
85 Use the standard configuration file for the systemwide message bus.
88 Print the version of the daemon.
90 .SH CONFIGURATION FILE
92 A message bus daemon has a configuration file that specializes it
93 for a particular application. For example, one configuration
94 file might set up the message bus to be a systemwide message bus,
95 while another might set it up to be a per-user-login-session bus.
98 The configuration file also establishes resource limits, security
99 parameters, and so forth.
102 The configuration file is not part of any interoperability
103 specification and its backward compatibility is not guaranteed; this
104 document is documentation, not specification.
107 The standard systemwide and per-session message bus setups are
108 configured in the files "@EXPANDED_SYSCONFDIR@/dbus-1/system.conf" and
109 "@EXPANDED_SYSCONFDIR@/dbus-1/session.conf". These files normally
110 <include> a system-local.conf or session-local.conf; you can put local
111 overrides in those files to avoid modifying the primary configuration
115 The configuration file is an XML document. It must have the following
119 <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
120 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
125 The following elements may be present in the configuration file.
137 The well-known type of the message bus. Currently known values are
138 "system" and "session"; if other values are set, they should be
139 either added to the D-BUS specification, or namespaced. The last
140 <type> element "wins" (previous values are ignored).
143 Example: <type>session</type>
149 Include a file <include>filename.conf</include> at this point. If the
150 filename is relative, it is located relative to the configuration file
154 <include> has an optional attribute "ignore_missing=(yes|no)"
155 which defaults to "no" if not provided. This attribute
156 controls whether it's a fatal error for the included file
163 Include all files in <includedir>foo.d</includedir> at this
164 point. Files in the directory are included in undefined order.
165 Only files ending in ".conf" are included.
168 This is intended to allow extension of the system bus by particular
169 packages. For example, if CUPS wants to be able to send out
170 notification of printer queue changes, it could install a file to
171 @EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
172 this message and allowed the printer daemon user to send it.
178 The user account the daemon should run as, as either a username or a
179 UID. If the daemon cannot change to this UID on startup, it will exit.
180 If this element is not present, the daemon will not change or care
184 The last <user> entry in the file "wins", the others are ignored.
187 The user is changed after the bus has completed initialization. So
188 sockets etc. will be created before changing user, but no data will be
189 read from clients before changing user. This means that sockets
190 and PID files can be created in a location that requires root
191 privileges for writing.
197 If present, the bus daemon becomes a real daemon (forks
198 into the background, etc.). This is generally used
199 rather than the \-\-fork command line option.
205 Add an address that the bus should listen on. The
206 address is in the standard D-BUS format that contains
207 a transport name plus possible parameters/options.
210 Example: <listen>unix:path=/tmp/foo</listen>
213 If there are multiple <listen> elements, then the bus listens
214 on multiple addresses. The bus will pass its address to
215 started services or other interested parties with
216 the last address given in <listen> first. That is,
217 apps will try to connect to the last <listen> address first.
223 Lists permitted authorization mechanisms. If this element doesn't
224 exist, then all known mechanisms are allowed. If there are multiple
225 <auth> elements, all the listed mechanisms are allowed. The order in
226 which mechanisms are listed is not meaningful.
229 Example: <auth>EXTERNAL</auth>
232 Example: <auth>DBUS_COOKIE_SHA1</auth>
238 Adds a directory to scan for .service files. Directories are
239 scanned starting with the last to appear in the config file
240 (the first .service file found that provides a particular
241 service will be used).
244 Service files tell the bus how to automatically start a program.
245 They are primarily used with the per-user-session bus,
246 not the systemwide bus.
252 <limit> establishes a resource limit. For example:
254 <limit name="max_message_size">64</limit>
255 <limit name="max_completed_connections">512</limit>
259 The name attribute is mandatory.
260 Available limit names are:
262 "max_incoming_bytes" : total size in bytes of messages
263 incoming from a single connection
264 "max_outgoing_bytes" : total size in bytes of messages
265 queued up for a single connection
266 "max_message_size" : max size of a single message in
268 "service_start_timeout" : milliseconds (thousandths) until
269 a started service has to connect
270 "auth_timeout" : milliseconds (thousandths) a
271 connection is given to
273 "max_completed_connections" : max number of authenticated connections
274 "max_incomplete_connections" : max number of unauthenticated
276 "max_connections_per_user" : max number of completed connections from
278 "max_pending_service_starts" : max number of service launches in
279 progress at the same time
280 "max_names_per_connection" : max number of names a single
282 "max_match_rules_per_connection": max number of match rules for a single
284 "max_replies_per_connection" : max number of pending method
285 replies per connection
286 (number of calls-in-progress)
287 "reply_timeout" : milliseconds (thousandths)
288 until a method call times out
292 The max incoming/outgoing queue sizes allow a new message to be queued
293 if one byte remains below the max. So you can in fact exceed the max
297 max_completed_connections divided by max_connections_per_user is the
298 number of users that can work together to denial-of-service all other users by using
299 up all connections on the systemwide bus.
302 Limits are normally only of interest on the systemwide bus, not the user session
309 The <policy> element defines a security policy to be applied to a particular
310 set of connections to the bus. A policy is made up of
311 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
312 they are analogous to a firewall in that they allow expected traffic
313 and prevent unexpected traffic.
316 The <policy> element has one of three attributes:
318 context="(default|mandatory)"
319 user="username or userid"
320 group="group name or gid"
325 Policies are applied to a connection as follows:
327 - all context="default" policies are applied
328 - all group="connection's user's group" policies are applied
330 - all user="connection's auth user" policies are applied
332 - all context="mandatory" policies are applied
336 Policies applied later will override those applied earlier,
337 when the policies overlap. Multiple policies with the same
338 user/group/context are applied in the order they appear
346 A <deny> element appears below a <policy> element and prohibits some
347 action. The <allow> element makes an exception to previous <deny>
348 statements, and works just like <deny> but with the inverse meaning.
351 The possible attributes of these elements are:
353 send_interface="interface_name"
354 send_member="method_or_signal_name"
355 send_error="error_name"
356 send_destination="name"
357 send_type="method_call" | "method_return" | "signal" | "error"
358 send_path="/path/name"
360 receive_interface="interface_name"
361 receive_member="method_or_signal_name"
362 receive_error="error_name"
363 receive_sender="name"
364 receive_type="method_call" | "method_return" | "signal" | "error"
365 receive_path="/path/name"
367 send_requested_reply="true" | "false"
368 receive_requested_reply="true" | "false"
370 eavesdrop="true" | "false"
380 <deny send_interface="org.freedesktop.System" send_member="Reboot"/>
381 <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
382 <deny own="org.freedesktop.System"/>
383 <deny send_destination="org.freedesktop.System"/>
384 <deny receive_sender="org.freedesktop.System"/>
386 <deny group="enemies"/>
390 The <deny> element's attributes determine whether the deny "matches" a
391 particular action. If it matches, the action is denied (unless later
392 rules in the config file allow it).
395 send_destination and receive_sender rules mean that messages may not be
396 sent to or received from the *owner* of the given name, not that
397 they may not be sent *to that name*. That is, if a connection
398 owns services A, B, C, and sending to A is denied, sending to B or C
399 will not work either.
402 The other send_* and receive_* attributes are purely textual/by-value
403 matches against the given field in the message header.
406 "Eavesdropping" occurs when an application receives a message that
407 was explicitly addressed to a name the application does not own.
408 Eavesdropping thus only applies to messages that are addressed to
409 services (i.e. it does not apply to signals).
412 For <allow>, eavesdrop="true" indicates that the rule matches even
413 when eavesdropping. eavesdrop="false" is the default and means that
414 the rule only allows messages to go to their specified recipient.
415 For <deny>, eavesdrop="true" indicates that the rule matches
416 only when eavesdropping. eavesdrop="false" is the default for <deny>
417 also, but here it means that the rule applies always, even when
418 not eavesdropping. The eavesdrop attribute can only be combined with
419 receive rules (with receive_* attributes).
423 The [send|receive]_requested_reply attribute works similarly to the eavesdrop
424 attribute. It controls whether the <deny> or <allow> matches a reply
425 that is expected (corresponds to a previous method call message).
426 This attribute only makes sense for reply messages (errors and method
427 returns), and is ignored for other message types.
430 For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
431 only requested replies are allowed by the
432 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
436 For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
437 the rule matches only when the reply was not
438 requested. [send|receive]_requested_reply="true" indicates that the rule applies
439 always, regardless of pending reply state.
442 user and group denials mean that the given user or group may
443 not connect to the message bus.
446 For "name", "username", "groupname", etc.
447 the character "*" can be substituted, meaning "any." Complex globs
448 like "foo.bar.*" aren't allowed for now because they'd be work to
449 implement and maybe encourage sloppy security anyway.
452 It does not make sense to deny a user or group inside a <policy>
453 for a user or group; user/group denials can only be inside
454 context="default" or context="mandatory" policies.
457 A single <deny> rule may specify combinations of attributes such as
458 send_destination and send_interface and send_type. In this case, the
459 denial applies only if both attributes match the message being denied.
460 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
461 deny messages with the given interface AND the given bus name.
462 To get an OR effect you specify multiple <deny> rules.
465 You can't include both send_ and receive_ attributes on the same
466 rule, since "whether the message can be sent" and "whether it can be
467 received" are evaluated separately.
470 Be careful with send_interface/receive_interface, because the
471 interface field in messages is optional.
477 The <selinux> element contains settings related to Security Enhanced Linux.
484 An <associate> element appears below an <selinux> element and
485 creates a mapping. Right now only one kind of association is possible:
487 <associate own="org.freedesktop.Foobar" context="foo_t"/>
491 This means that if a connection asks to own the name
492 "org.freedesktop.Foobar" then the source context will be the context
493 of the connection and the target context will be "foo_t" - see the
494 short discussion of SELinux below.
497 Note, the context here is the target context when requesting a name,
498 NOT the context of the connection owning the name.
501 There's currently no way to set a default for owning any name, if
502 we add this syntax it will look like:
504 <associate own="*" context="foo_t"/>
506 If you find a reason this is useful, let the developers know.
507 Right now the default will be the security context of the bus itself.
510 If two <associate> elements specify the same name, the element
511 appearing later in the configuration file will be used.
516 See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:
519 Every subject (process) and object (e.g. file, socket, IPC object,
520 etc) in the system is assigned a collection of security attributes,
521 known as a security context. A security context contains all of the
522 security attributes associated with a particular subject or object
523 that are relevant to the security policy.
526 In order to better encapsulate security contexts and to provide
527 greater efficiency, the policy enforcement code of SELinux typically
528 handles security identifiers (SIDs) rather than security contexts. A
529 SID is an integer that is mapped by the security server to a security
533 When a security decision is required, the policy enforcement code
534 passes a pair of SIDs (typically the SID of a subject and the SID of
535 an object, but sometimes a pair of subject SIDs or a pair of object
536 SIDs), and an object security class to the security server. The object
537 security class indicates the kind of object, e.g. a process, a regular
538 file, a directory, a TCP socket, etc.
541 Access decisions specify whether or not a permission is granted for a
542 given pair of SIDs and class. Each object class has a set of
543 associated permissions defined to control operations on objects with
547 D-BUS performs SELinux security checks in two places.
550 First, any time a message is routed from one connection to another
551 connection, the bus daemon will check permissions with the security context of
552 the first connection as source, security context of the second connection
553 as target, object class "dbus" and requested permission "send_msg".
556 If a security context is not available for a connection
557 (impossible when using UNIX domain sockets), then the target
558 context used is the context of the bus daemon itself.
559 There is currently no way to change this default, because we're
560 assuming that only UNIX domain sockets will be used to
561 connect to the systemwide bus. If this changes, we'll
562 probably add a way to set the default connection context.
565 Second, any time a connection asks to own a name,
566 the bus daemon will check permissions with the security
567 context of the connection as source, the security context specified
568 for the name in the config file as target, object
569 class "dbus" and requested permission "acquire_svc".
572 The security context for a bus name is specified with the
573 <associate> element described earlier in this document.
574 If a name has no security context associated in the
575 configuration file, the security context of the bus daemon
579 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
582 Please send bug reports to the D-BUS mailing list or bug tracker,
583 see http://www.freedesktop.org/software/dbus/
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