2 .\" dbus\-daemon manual page.
3 .\" Copyright (C) 2003,2008 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]
15 \fIdbus\-daemon\fP is the D\-Bus message bus daemon. See
16 http://www.freedesktop.org/software/dbus/ for more information about
17 the big picture. D\-Bus is first a library that provides one\-to\-one
18 communication between any two applications; \fIdbus\-daemon\fP is an
19 application that uses this library to implement a message bus
20 daemon. Multiple programs connect to the message bus daemon and can
21 exchange messages with one another.
23 There are two standard message bus instances: the systemwide message bus
24 (installed on many systems as the "messagebus" init service) and the
25 per\-user\-login\-session message bus (started each time a user logs in).
26 \fIdbus\-daemon\fP is used for both of these instances, but with
27 a different configuration file.
29 The \-\-session option is equivalent to
30 "\-\-config\-file=@EXPANDED_SYSCONFDIR@/dbus\-1/session.conf" and the \-\-system
31 option is equivalent to
32 "\-\-config\-file=@EXPANDED_SYSCONFDIR@/dbus\-1/system.conf". By creating
33 additional configuration files and using the \-\-config\-file option,
34 additional special\-purpose message bus daemons could be created.
36 The systemwide daemon is normally launched by an init script,
37 standardly called simply "messagebus".
39 The systemwide daemon is largely used for broadcasting system events,
40 such as changes to the printer queue, or adding/removing devices.
42 The per\-session daemon is used for various interprocess communication
43 among desktop applications (however, it is not tied to X or the GUI
46 SIGHUP will cause the D\-Bus daemon to PARTIALLY reload its
47 configuration file and to flush its user/group information caches. Some
48 configuration changes would require kicking all apps off the bus; so they will
49 only take effect if you restart the daemon. Policy changes should take effect
53 The following options are supported:
55 .I "\-\-config\-file=FILE"
56 Use the given configuration file.
59 Force the message bus to fork and become a daemon, even if
60 the configuration file does not specify that it should.
61 In most contexts the configuration file already gets this
64 Force the message bus not to fork and become a daemon, even if
65 the configuration file specifies that it should.
67 .I "\-\-print\-address[=DESCRIPTOR]"
68 Print the address of the message bus to standard output, or
69 to the given file descriptor. This is used by programs that
70 launch the message bus.
72 .I "\-\-print\-pid[=DESCRIPTOR]"
73 Print the process ID of the message bus to standard output, or
74 to the given file descriptor. This is used by programs that
75 launch the message bus.
78 Use the standard configuration file for the per\-login\-session message
82 Use the standard configuration file for the systemwide message bus.
85 Print the version of the daemon.
88 Print the introspection information for all D\-Bus internal interfaces.
90 .I "\-\-address[=ADDRESS]"
91 Set the address to listen on. This option overrides the address
92 configured in the configuration file.
94 .I "\-\-systemd\-activation"
95 Enable systemd\-style service activation. Only useful in conjunction
96 with the systemd system and session manager on Linux.
98 .SH CONFIGURATION FILE
100 A message bus daemon has a configuration file that specializes it
101 for a particular application. For example, one configuration
102 file might set up the message bus to be a systemwide message bus,
103 while another might set it up to be a per\-user\-login\-session bus.
105 The configuration file also establishes resource limits, security
106 parameters, and so forth.
108 The configuration file is not part of any interoperability
109 specification and its backward compatibility is not guaranteed; this
110 document is documentation, not specification.
112 The standard systemwide and per\-session message bus setups are
113 configured in the files "@EXPANDED_SYSCONFDIR@/dbus\-1/system.conf" and
114 "@EXPANDED_SYSCONFDIR@/dbus\-1/session.conf". These files normally
115 <include> a system\-local.conf or session\-local.conf; you can put local
116 overrides in those files to avoid modifying the primary configuration
120 The configuration file is an XML document. It must have the following
124 <!DOCTYPE busconfig PUBLIC "\-//freedesktop//DTD D\-Bus Bus Configuration 1.0//EN"
125 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
130 The following elements may be present in the configuration file.
142 The well\-known type of the message bus. Currently known values are
143 "system" and "session"; if other values are set, they should be
144 either added to the D\-Bus specification, or namespaced. The last
145 <type> element "wins" (previous values are ignored). This element
146 only controls which message bus specific environment variables are
147 set in activated clients. Most of the policy that distinguishes a
148 session bus from the system bus is controlled from the other elements
149 in the configuration file.
152 If the well\-known type of the message bus is "session", then the
153 DBUS_STARTER_BUS_TYPE environment variable will be set to "session"
154 and the DBUS_SESSION_BUS_ADDRESS environment variable will be set
155 to the address of the session bus. Likewise, if the type of the
156 message bus is "system", then the DBUS_STARTER_BUS_TYPE environment
157 variable will be set to "system" and the DBUS_SESSION_BUS_ADDRESS
158 environment variable will be set to the address of the system bus
159 (which is normally well known anyway).
162 Example: <type>session</type>
168 Include a file <include>filename.conf</include> at this point. If the
169 filename is relative, it is located relative to the configuration file
173 <include> has an optional attribute "ignore_missing=(yes|no)"
174 which defaults to "no" if not provided. This attribute
175 controls whether it's a fatal error for the included file
182 Include all files in <includedir>foo.d</includedir> at this
183 point. Files in the directory are included in undefined order.
184 Only files ending in ".conf" are included.
187 This is intended to allow extension of the system bus by particular
188 packages. For example, if CUPS wants to be able to send out
189 notification of printer queue changes, it could install a file to
190 @EXPANDED_SYSCONFDIR@/dbus\-1/system.d that allowed all apps to receive
191 this message and allowed the printer daemon user to send it.
197 The user account the daemon should run as, as either a username or a
198 UID. If the daemon cannot change to this UID on startup, it will exit.
199 If this element is not present, the daemon will not change or care
203 The last <user> entry in the file "wins", the others are ignored.
206 The user is changed after the bus has completed initialization. So
207 sockets etc. will be created before changing user, but no data will be
208 read from clients before changing user. This means that sockets
209 and PID files can be created in a location that requires root
210 privileges for writing.
216 If present, the bus daemon becomes a real daemon (forks
217 into the background, etc.). This is generally used
218 rather than the \-\-fork command line option.
224 If present, the bus daemon keeps its original umask when forking.
225 This may be useful to avoid affecting the behavior of child processes.
231 Add an address that the bus should listen on. The
232 address is in the standard D\-Bus format that contains
233 a transport name plus possible parameters/options.
236 Example: <listen>unix:path=/tmp/foo</listen>
239 Example: <listen>tcp:host=localhost,port=1234</listen>
242 If there are multiple <listen> elements, then the bus listens
243 on multiple addresses. The bus will pass its address to
244 started services or other interested parties with
245 the last address given in <listen> first. That is,
246 apps will try to connect to the last <listen> address first.
249 tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.
250 If a hostname resolves to multiple addresses, the server will bind
251 to all of them. The family=ipv4 or family=ipv6 options can be used
252 to force it to bind to a subset of addresses
255 Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen>
258 A special case is using a port number of zero (or omitting the port),
259 which means to choose an available port selected by the operating
260 system. The port number chosen can be obtained with the
261 \-\-print\-address command line parameter and will be present in other
262 cases where the server reports its own address, such as when
263 DBUS_SESSION_BUS_ADDRESS is set.
266 Example: <listen>tcp:host=localhost,port=0</listen>
269 tcp addresses also allow a bind=hostname option, which will override
270 the host option specifying what address to bind to, without changing
271 the address reported by the bus. The bind option can also take a
272 special name '*' to cause the bus to listen on all local address
273 (INADDR_ANY). The specified host should be a valid name of the local
274 machine or weird stuff will happen.
277 Example: <listen>tcp:host=localhost,bind=*,port=0</listen>
283 Lists permitted authorization mechanisms. If this element doesn't
284 exist, then all known mechanisms are allowed. If there are multiple
285 <auth> elements, all the listed mechanisms are allowed. The order in
286 which mechanisms are listed is not meaningful.
289 Example: <auth>EXTERNAL</auth>
292 Example: <auth>DBUS_COOKIE_SHA1</auth>
298 Adds a directory to scan for .service files. Directories are
299 scanned starting with the last to appear in the config file
300 (the first .service file found that provides a particular
301 service will be used).
304 Service files tell the bus how to automatically start a program.
305 They are primarily used with the per\-user\-session bus,
306 not the systemwide bus.
309 .I "<standard_session_servicedirs/>"
312 <standard_session_servicedirs/> is equivalent to specifying a series
313 of <servicedir/> elements for each of the data directories in the "XDG
314 Base Directory Specification" with the subdirectory "dbus\-1/services",
315 so for example "/usr/share/dbus\-1/services" would be among the
316 directories searched.
319 The "XDG Base Directory Specification" can be found at
320 http://freedesktop.org/wiki/Standards/basedir\-spec if it hasn't moved,
321 otherwise try your favorite search engine.
324 The <standard_session_servicedirs/> option is only relevant to the
325 per\-user\-session bus daemon defined in
326 @EXPANDED_SYSCONFDIR@/dbus\-1/session.conf. Putting it in any other
327 configuration file would probably be nonsense.
330 .I "<standard_system_servicedirs/>"
333 <standard_system_servicedirs/> specifies the standard system\-wide
334 activation directories that should be searched for service files.
335 This option defaults to @EXPANDED_DATADIR@/dbus\-1/system\-services.
338 The <standard_system_servicedirs/> option is only relevant to the
339 per\-system bus daemon defined in
340 @EXPANDED_SYSCONFDIR@/dbus\-1/system.conf. Putting it in any other
341 configuration file would probably be nonsense.
344 .I "<servicehelper/>"
347 <servicehelper/> specifies the setuid helper that is used to launch
348 system daemons with an alternate user. Typically this should be
349 the dbus\-daemon\-launch\-helper executable in located in libexec.
352 The <servicehelper/> option is only relevant to the per\-system bus daemon
353 defined in @EXPANDED_SYSCONFDIR@/dbus\-1/system.conf. Putting it in any other
354 configuration file would probably be nonsense.
360 <limit> establishes a resource limit. For example:
362 <limit name="max_message_size">64</limit>
363 <limit name="max_completed_connections">512</limit>
367 The name attribute is mandatory.
368 Available limit names are:
370 "max_incoming_bytes" : total size in bytes of messages
371 incoming from a single connection
372 "max_incoming_unix_fds" : total number of unix fds of messages
373 incoming from a single connection
374 "max_outgoing_bytes" : total size in bytes of messages
375 queued up for a single connection
376 "max_outgoing_unix_fds" : total number of unix fds of messages
377 queued up for a single connection
378 "max_message_size" : max size of a single message in
380 "max_message_unix_fds" : max unix fds of a single message
381 "service_start_timeout" : milliseconds (thousandths) until
382 a started service has to connect
383 "auth_timeout" : milliseconds (thousandths) a
384 connection is given to
386 "max_completed_connections" : max number of authenticated connections
387 "max_incomplete_connections" : max number of unauthenticated
389 "max_connections_per_user" : max number of completed connections from
391 "max_pending_service_starts" : max number of service launches in
392 progress at the same time
393 "max_names_per_connection" : max number of names a single
395 "max_match_rules_per_connection": max number of match rules for a single
397 "max_replies_per_connection" : max number of pending method
398 replies per connection
399 (number of calls\-in\-progress)
400 "reply_timeout" : milliseconds (thousandths)
401 until a method call times out
405 The max incoming/outgoing queue sizes allow a new message to be queued
406 if one byte remains below the max. So you can in fact exceed the max
410 max_completed_connections divided by max_connections_per_user is the
411 number of users that can work together to denial\-of\-service all other users by using
412 up all connections on the systemwide bus.
415 Limits are normally only of interest on the systemwide bus, not the user session
422 The <policy> element defines a security policy to be applied to a particular
423 set of connections to the bus. A policy is made up of
424 <allow> and <deny> elements. Policies are normally used with the systemwide bus;
425 they are analogous to a firewall in that they allow expected traffic
426 and prevent unexpected traffic.
429 Currently, the system bus has a default\-deny policy for sending method calls
430 and owning bus names. Everything else, in particular reply messages, receive
431 checks, and signals has a default allow policy.
434 In general, it is best to keep system services as small, targeted programs which
435 run in their own process and provide a single bus name. Then, all that is needed
436 is an <allow> rule for the "own" permission to let the process claim the bus
437 name, and a "send_destination" rule to allow traffic from some or all uids to
441 The <policy> element has one of four attributes:
443 context="(default|mandatory)"
444 at_console="(true|false)"
445 user="username or userid"
446 group="group name or gid"
450 Policies are applied to a connection as follows:
452 \- all context="default" policies are applied
453 \- all group="connection's user's group" policies are applied
455 \- all user="connection's auth user" policies are applied
457 \- all at_console="true" policies are applied
458 \- all at_console="false" policies are applied
459 \- all context="mandatory" policies are applied
463 Policies applied later will override those applied earlier,
464 when the policies overlap. Multiple policies with the same
465 user/group/context are applied in the order they appear
473 A <deny> element appears below a <policy> element and prohibits some
474 action. The <allow> element makes an exception to previous <deny>
475 statements, and works just like <deny> but with the inverse meaning.
478 The possible attributes of these elements are:
480 send_interface="interface_name"
481 send_member="method_or_signal_name"
482 send_error="error_name"
483 send_destination="name"
484 send_type="method_call" | "method_return" | "signal" | "error"
485 send_path="/path/name"
487 receive_interface="interface_name"
488 receive_member="method_or_signal_name"
489 receive_error="error_name"
490 receive_sender="name"
491 receive_type="method_call" | "method_return" | "signal" | "error"
492 receive_path="/path/name"
494 send_requested_reply="true" | "false"
495 receive_requested_reply="true" | "false"
497 eavesdrop="true" | "false"
507 <deny send_destination="org.freedesktop.Service" send_interface="org.freedesktop.System" send_member="Reboot"/>
508 <deny send_destination="org.freedesktop.System"/>
509 <deny receive_sender="org.freedesktop.System"/>
511 <deny group="enemies"/>
515 The <deny> element's attributes determine whether the deny "matches" a
516 particular action. If it matches, the action is denied (unless later
517 rules in the config file allow it).
519 send_destination and receive_sender rules mean that messages may not be
520 sent to or received from the *owner* of the given name, not that
521 they may not be sent *to that name*. That is, if a connection
522 owns services A, B, C, and sending to A is denied, sending to B or C
523 will not work either.
525 The other send_* and receive_* attributes are purely textual/by\-value
526 matches against the given field in the message header.
528 "Eavesdropping" occurs when an application receives a message that
529 was explicitly addressed to a name the application does not own, or
530 is a reply to such a message. Eavesdropping thus only applies to
531 messages that are addressed to services and replies to such messages
532 (i.e. it does not apply to signals).
534 For <allow>, eavesdrop="true" indicates that the rule matches even
535 when eavesdropping. eavesdrop="false" is the default and means that
536 the rule only allows messages to go to their specified recipient.
537 For <deny>, eavesdrop="true" indicates that the rule matches
538 only when eavesdropping. eavesdrop="false" is the default for <deny>
539 also, but here it means that the rule applies always, even when
540 not eavesdropping. The eavesdrop attribute can only be combined with
541 send and receive rules (with send_* and receive_* attributes).
543 The [send|receive]_requested_reply attribute works similarly to the eavesdrop
544 attribute. It controls whether the <deny> or <allow> matches a reply
545 that is expected (corresponds to a previous method call message).
546 This attribute only makes sense for reply messages (errors and method
547 returns), and is ignored for other message types.
550 For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
551 only requested replies are allowed by the
552 rule. [send|receive]_requested_reply="false" means that the rule allows any reply
556 For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
557 the rule matches only when the reply was not
558 requested. [send|receive]_requested_reply="true" indicates that the rule applies
559 always, regardless of pending reply state.
562 user and group denials mean that the given user or group may
563 not connect to the message bus.
566 For "name", "username", "groupname", etc.
567 the character "*" can be substituted, meaning "any." Complex globs
568 like "foo.bar.*" aren't allowed for now because they'd be work to
569 implement and maybe encourage sloppy security anyway.
572 It does not make sense to deny a user or group inside a <policy>
573 for a user or group; user/group denials can only be inside
574 context="default" or context="mandatory" policies.
577 A single <deny> rule may specify combinations of attributes such as
578 send_destination and send_interface and send_type. In this case, the
579 denial applies only if both attributes match the message being denied.
580 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
581 deny messages with the given interface AND the given bus name.
582 To get an OR effect you specify multiple <deny> rules.
585 You can't include both send_ and receive_ attributes on the same
586 rule, since "whether the message can be sent" and "whether it can be
587 received" are evaluated separately.
590 Be careful with send_interface/receive_interface, because the
591 interface field in messages is optional. In particular, do NOT
592 specify <deny send_interface="org.foo.Bar"/>! This will cause
593 no\-interface messages to be blocked for all services, which is
594 almost certainly not what you intended. Always use rules of
595 the form: <deny send_interface="org.foo.Bar" send_destination="org.foo.Service"/>
601 The <selinux> element contains settings related to Security Enhanced Linux.
608 An <associate> element appears below an <selinux> element and
609 creates a mapping. Right now only one kind of association is possible:
611 <associate own="org.freedesktop.Foobar" context="foo_t"/>
615 This means that if a connection asks to own the name
616 "org.freedesktop.Foobar" then the source context will be the context
617 of the connection and the target context will be "foo_t" \- see the
618 short discussion of SELinux below.
621 Note, the context here is the target context when requesting a name,
622 NOT the context of the connection owning the name.
625 There's currently no way to set a default for owning any name, if
626 we add this syntax it will look like:
628 <associate own="*" context="foo_t"/>
630 If you find a reason this is useful, let the developers know.
631 Right now the default will be the security context of the bus itself.
634 If two <associate> elements specify the same name, the element
635 appearing later in the configuration file will be used.
640 See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:
643 Every subject (process) and object (e.g. file, socket, IPC object,
644 etc) in the system is assigned a collection of security attributes,
645 known as a security context. A security context contains all of the
646 security attributes associated with a particular subject or object
647 that are relevant to the security policy.
650 In order to better encapsulate security contexts and to provide
651 greater efficiency, the policy enforcement code of SELinux typically
652 handles security identifiers (SIDs) rather than security contexts. A
653 SID is an integer that is mapped by the security server to a security
657 When a security decision is required, the policy enforcement code
658 passes a pair of SIDs (typically the SID of a subject and the SID of
659 an object, but sometimes a pair of subject SIDs or a pair of object
660 SIDs), and an object security class to the security server. The object
661 security class indicates the kind of object, e.g. a process, a regular
662 file, a directory, a TCP socket, etc.
665 Access decisions specify whether or not a permission is granted for a
666 given pair of SIDs and class. Each object class has a set of
667 associated permissions defined to control operations on objects with
671 D\-Bus performs SELinux security checks in two places.
674 First, any time a message is routed from one connection to another
675 connection, the bus daemon will check permissions with the security context of
676 the first connection as source, security context of the second connection
677 as target, object class "dbus" and requested permission "send_msg".
680 If a security context is not available for a connection
681 (impossible when using UNIX domain sockets), then the target
682 context used is the context of the bus daemon itself.
683 There is currently no way to change this default, because we're
684 assuming that only UNIX domain sockets will be used to
685 connect to the systemwide bus. If this changes, we'll
686 probably add a way to set the default connection context.
689 Second, any time a connection asks to own a name,
690 the bus daemon will check permissions with the security
691 context of the connection as source, the security context specified
692 for the name in the config file as target, object
693 class "dbus" and requested permission "acquire_svc".
696 The security context for a bus name is specified with the
697 <associate> element described earlier in this document.
698 If a name has no security context associated in the
699 configuration file, the security context of the bus daemon
705 If you're trying to figure out where your messages are going or why
706 you aren't getting messages, there are several things you can try.
708 Remember that the system bus is heavily locked down and if you
709 haven't installed a security policy file to allow your message
710 through, it won't work. For the session bus, this is not a concern.
712 The simplest way to figure out what's happening on the bus is to run
713 the \fIdbus\-monitor\fP program, which comes with the D\-Bus
714 package. You can also send test messages with \fIdbus\-send\fP. These
715 programs have their own man pages.
717 If you want to know what the daemon itself is doing, you might consider
718 running a separate copy of the daemon to test against. This will allow you
719 to put the daemon under a debugger, or run it with verbose output, without
720 messing up your real session and system daemons.
722 To run a separate test copy of the daemon, for example you might open a terminal
725 DBUS_VERBOSE=1 dbus\-daemon \-\-session \-\-print\-address
728 The test daemon address will be printed when the daemon starts. You will need
729 to copy\-and\-paste this address and use it as the value of the
730 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
731 you want to test. This will cause those applications to connect to your
732 test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.
734 DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D\-Bus
735 was compiled with verbose mode enabled. This is not recommended in
736 production builds due to performance impact. You may need to rebuild
737 D\-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
738 also affects the D\-Bus library and thus applications using D\-Bus; it may
739 be useful to see verbose output on both the client side and from the daemon.)
741 If you want to get fancy, you can create a custom bus
742 configuration for your test bus (see the session.conf and system.conf
743 files that define the two default configurations for example). This
744 would allow you to specify a different directory for .service files,
748 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
751 Please send bug reports to the D\-Bus mailing list or bug tracker,
752 see http://www.freedesktop.org/software/dbus/