1dbus-daemon(1) General Commands Manual dbus-daemon(1)
2
6 dbus-daemon - Message bus daemon
7
9 dbus-daemon dbus-daemon [--version] [--session] [--system] [--config-
10 file=FILE] [--print-address[=DESCRIPTOR]] [--print-pid[=DESCRIPTOR]]
11 [--fork]
12
15 dbus-daemon is the D-Bus message bus daemon. See http://www.freedesk‐
16 top.org/software/dbus/ for more information about the big picture. D-
17 Bus is first a library that provides one-to-one communication between
18 any two applications; dbus-daemon is an application that uses this
19 library to implement a message bus daemon. Multiple programs connect to
20 the message bus daemon and can exchange messages with one another.
21 There are two standard message bus instances: the systemwide message
24 bus (installed on many systems as the "messagebus" init service) and
25 the per-user-login-session message bus (started each time a user logs
26 in). dbus-daemon is used for both of these instances, but with a dif‐
27 ferent configuration file.
28 The --session option is equivalent to "--config-file=/etc/dbus-1/ses‐
31 sion.conf" and the --system option is equivalent to "--config-
32 file=/etc/dbus-1/system.conf". By creating additional configuration
33 files and using the --config-file option, additional special-purpose
34 message bus daemons could be created.
35 The systemwide daemon is normally launched by an init script, stan‐
38 dardly called simply "messagebus".
39 The systemwide daemon is largely used for broadcasting system events,
42 such as changes to the printer queue, or adding/removing devices.
43 The per-session daemon is used for various interprocess communication
46 among desktop applications (however, it is not tied to X or the GUI in
47 any way).
48 SIGHUP will cause the D-Bus daemon to PARTIALLY reload its configura‐
51 tion file and to flush its user/group information caches. Some configu‐
52 ration changes would require kicking all apps off the bus; so they will
53 only take effect if you restart the daemon. Policy changes should take
54 effect with SIGHUP.
55
58 The following options are supported:
59 --config-file=FILE
61 Use the given configuration file.
62 --fork Force the message bus to fork and become a daemon, even if the
64 configuration file does not specify that it should. In most
65 contexts the configuration file already gets this right, though.
66 --print-address[=DESCRIPTOR]
68 Print the address of the message bus to standard output, or to
69 the given file descriptor. This is used by programs that launch
70 the message bus.
71 --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.
76 --session
78 Use the standard configuration file for the per-login-session
79 message bus.
80 --system
82 Use the standard configuration file for the systemwide message
83 bus.
84 --version
86 Print the version of the daemon.
87
90 A message bus daemon has a configuration file that specializes it for a
91 particular application. For example, one configuration file might set
92 up the message bus to be a systemwide message bus, while another might
93 set it up to be a per-user-login-session bus.
94 The configuration file also establishes resource limits, security
97 parameters, and so forth.
98 The configuration file is not part of any interoperability specifica‐
101 tion and its backward compatibility is not guaranteed; this document is
102 documentation, not specification.
103 The standard systemwide and per-session message bus setups are config‐
106 ured in the files "/etc/dbus-1/system.conf" and "/etc/dbus-1/ses‐
107 sion.conf". These files normally <include> a system-local.conf or ses‐
108 sion-local.conf; you can put local overrides in those files to avoid
109 modifying the primary configuration files.
110 The configuration file is an XML document. It must have the following
113 doctype declaration:
114 <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
116 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
117 The following elements may be present in the configuration file.
121 <busconfig>
124 Root element.
127 <type>
130 The well-known type of the message bus. Currently known values are
133 "system" and "session"; if other values are set, they should be either
134 added to the D-Bus specification, or namespaced. The last <type> ele‐
135 ment "wins" (previous values are ignored). This element only controls
136 which message bus specific environment variables are set in activated
137 clients. Most of the policy that distinguishes a session bus from the
138 system bus is controlled from the other elements in the configuration
139 file.
140 If the well-known type of the message bus is "session", then the
143 DBUS_STARTER_BUS_TYPE environment variable will be set to "session" and
144 the DBUS_SESSION_BUS_ADDRESS environment variable will be set to the
145 address of the session bus. Likewise, if the type of the message bus
146 is "system", then the DBUS_STARTER_BUS_TYPE environment variable will
147 be set to "system" and the DBUS_SESSION_BUS_ADDRESS environment vari‐
148 able will be set to the address of the system bus (which is normally
149 well known anyway).
150 Example: <type>session</type>
153 <include>
156 Include a file <include>filename.conf</include> at this point. If the
159 filename is relative, it is located relative to the configuration file
160 doing the including.
161 <include> has an optional attribute "ignore_missing=(yes|no)" which
164 defaults to "no" if not provided. This attribute controls whether it's
165 a fatal error for the included file to be absent.
166 <includedir>
169 Include all files in <includedir>foo.d</includedir> at this point.
172 Files in the directory are included in undefined order. Only files
173 ending in ".conf" are included.
174 This is intended to allow extension of the system bus by particular
177 packages. For example, if CUPS wants to be able to send out notifica‐
178 tion of printer queue changes, it could install a file to
179 /etc/dbus-1/system.d that allowed all apps to receive this message and
180 allowed the printer daemon user to send it.
181 <user>
184 The user account the daemon should run as, as either a username or a
187 UID. If the daemon cannot change to this UID on startup, it will exit.
188 If this element is not present, the daemon will not change or care
189 about its UID.
190 The last <user> entry in the file "wins", the others are ignored.
193 The user is changed after the bus has completed initialization. So
196 sockets etc. will be created before changing user, but no data will be
197 read from clients before changing user. This means that sockets and PID
198 files can be created in a location that requires root privileges for
199 writing.
200 <fork>
203 If present, the bus daemon becomes a real daemon (forks into the back‐
206 ground, etc.). This is generally used rather than the --fork command
207 line option.
208 <keep_umask>
211 If present, the bus daemon keeps its original umask when forking. This
214 may be useful to avoid affecting the behavior of child processes.
215 <listen>
218 Add an address that the bus should listen on. The address is in the
221 standard D-Bus format that contains a transport name plus possible
222 parameters/options.
223 Example: <listen>unix:path=/tmp/foo</listen>
226 Example: <listen>tcp:host=localhost,port=1234</listen>
229 If there are multiple <listen> elements, then the bus listens on multi‐
232 ple addresses. The bus will pass its address to started services or
233 other interested parties with the last address given in <listen> first.
234 That is, apps will try to connect to the last <listen> address first.
235 tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames. If
238 a hostname resolves to multiple addresses, the server will bind to all
239 of them. The family=ipv4 or family=ipv6 options can be used to force it
240 to bind to a subset of addresses
241 Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen>
244 A special case is using a port number of zero (or omitting the port),
247 which means to choose an available port selected by the operating sys‐
248 tem. The port number chosen can be obtained with the --print-address
249 command line parameter and will be present in other cases where the
250 server reports its own address, such as when DBUS_SESSION_BUS_ADDRESS
251 is set.
252 Example: <listen>tcp:host=localhost,port=0</listen>
255 tcp addresses also allow a bind=hostname option, which will override
258 the host option specifying what address to bind to, without changing
259 the address reported by the bus. The bind option can also take a spe‐
260 cial name '*' to cause the bus to listen on all local address
261 (INADDR_ANY). The specified host should be a valid name of the local
262 machine or weird stuff will happen.
263 Example: <listen>tcp:host=localhost,bind=*,port=0</listen>
266 <auth>
269 Lists permitted authorization mechanisms. If this element doesn't
272 exist, then all known mechanisms are allowed. If there are multiple
273 <auth> elements, all the listed mechanisms are allowed. The order in
274 which mechanisms are listed is not meaningful.
275 Example: <auth>EXTERNAL</auth>
278 Example: <auth>DBUS_COOKIE_SHA1</auth>
281 <servicedir>
284 Adds a directory to scan for .service files. Directories are scanned
287 starting with the last to appear in the config file (the first .service
288 file found that provides a particular service will be used).
289 Service files tell the bus how to automatically start a program. They
292 are primarily used with the per-user-session bus, not the systemwide
293 bus.
294 <standard_session_servicedirs/>
297 <standard_session_servicedirs/> is equivalent to specifying a series of
300 <servicedir/> elements for each of the data directories in the "XDG
301 Base Directory Specification" with the subdirectory "dbus-1/services",
302 so for example "/usr/share/dbus-1/services" would be among the directo‐
303 ries searched.
304 The "XDG Base Directory Specification" can be found at http://freedesk‐
307 top.org/wiki/Standards/basedir-spec if it hasn't moved, otherwise try
308 your favorite search engine.
309 The <standard_session_servicedirs/> option is only relevant to the per-
312 user-session bus daemon defined in /etc/dbus-1/session.conf. Putting it
313 in any other configuration file would probably be nonsense.
314 <standard_system_servicedirs/>
317 <standard_system_servicedirs/> specifies the standard system-wide acti‐
320 vation directories that should be searched for service files. This
321 option defaults to /usr/share/dbus-1/system-services.
322 The <standard_system_servicedirs/> option is only relevant to the per-
325 system bus daemon defined in /etc/dbus-1/system.conf. Putting it in any
326 other configuration file would probably be nonsense.
327 <servicehelper/>
330 <servicehelper/> specifies the setuid helper that is used to launch
333 system daemons with an alternate user. Typically this should be the
334 dbus-daemon-launch-helper executable in located in libexec.
335 The <servicehelper/> option is only relevant to the per-system bus dae‐
338 mon defined in /etc/dbus-1/system.conf. Putting it in any other config‐
339 uration file would probably be nonsense.
340 <limit>
343 <limit> establishes a resource limit. For example:
346 <limit name="max_message_size">64</limit>
347 <limit name="max_completed_connections">512</limit>
348 The name attribute is mandatory. Available limit names are:
351 "max_incoming_bytes" : total size in bytes of messages
352 incoming from a single connection
353 "max_outgoing_bytes" : total size in bytes of messages
354 queued up for a single connection
355 "max_message_size" : max size of a single message in
356 bytes
357 "service_start_timeout" : milliseconds (thousandths) until
358 a started service has to connect
359 "auth_timeout" : milliseconds (thousandths) a
360 connection is given to
361 authenticate
362 "max_completed_connections" : max number of authenticated connections
363 "max_incomplete_connections" : max number of unauthenticated
364 connections
365 "max_connections_per_user" : max number of completed connections from
366 the same user
367 "max_pending_service_starts" : max number of service launches in
368 progress at the same time
369 "max_names_per_connection" : max number of names a single
370 connection can own
371 "max_match_rules_per_connection": max number of match rules for a single
372 connection
373 "max_replies_per_connection" : max number of pending method
374 replies per connection
375 (number of calls-in-progress)
376 "reply_timeout" : milliseconds (thousandths)
377 until a method call times out
378 The max incoming/outgoing queue sizes allow a new message to be queued
381 if one byte remains below the max. So you can in fact exceed the max by
382 max_message_size.
383 max_completed_connections divided by max_connections_per_user is the
386 number of users that can work together to denial-of-service all other
387 users by using up all connections on the systemwide bus.
388 Limits are normally only of interest on the systemwide bus, not the
391 user session buses.
392 <policy>
395 The <policy> element defines a security policy to be applied to a par‐
398 ticular set of connections to the bus. A policy is made up of <allow>
399 and <deny> elements. Policies are normally used with the systemwide
400 bus; they are analogous to a firewall in that they allow expected traf‐
401 fic and prevent unexpected traffic.
402 Currently, the system bus has a default-deny policy for sending method
405 calls and owning bus names. Everything else, in particular reply mes‐
406 sages, receive checks, and signals has a default allow policy.
407 In general, it is best to keep system services as small, targeted pro‐
410 grams which run in their own process and provide a single bus name.
411 Then, all that is needed is an <allow> rule for the "own" permission to
412 let the process claim the bus name, and a "send_destination" rule to
413 allow traffic from some or all uids to your service.
414 The <policy> element has one of four attributes: daemon.1.in
417 context="(default|mandatory)"
418 at_console="(true|false)"
419 user="username or userid"
420 group="group name or gid"
421 Policies are applied to a connection as follows:
424 - all context="default" policies are applied
425 - all group="connection's user's group" policies are applied
426 in undefined order
427 - all user="connection's auth user" policies are applied
428 in undefined order
429 - all at_console="true" policies are applied
430 - all at_console="false" policies are applied
431 - all context="mandatory" policies are applied
432 Policies applied later will override those applied earlier, when the
435 policies overlap. Multiple policies with the same user/group/context
436 are applied in the order they appear in the config file.
437 <deny> <allow>
440 A <deny> element appears below a <policy> element and prohibits some
443 action. The <allow> element makes an exception to previous <deny>
444 statements, and works just like <deny> but with the inverse meaning.
445 The possible attributes of these elements are:
448 send_interface="interface_name"
449 send_member="method_or_signal_name"
450 send_error="error_name"
451 send_destination="name"
452 send_type="method_call" | "method_return" | "signal" | "error"
453 send_path="/path/name"
454 receive_interface="interface_name"
456 receive_member="method_or_signal_name"
457 receive_error="error_name"
458 receive_sender="name"
459 receive_type="method_call" | "method_return" | "signal" | "error"
460 receive_path="/path/name"
461 send_requested_reply="true" | "false"
463 receive_requested_reply="true" | "false"
464 eavesdrop="true" | "false"
466 own="name"
468 user="username"
469 group="groupname"
470 Examples:
473 <deny send_interface="org.freedesktop.System" send_member="Reboot"/>
474 <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
475 <deny own="org.freedesktop.System"/>
476 <deny send_destination="org.freedesktop.System"/>
477 <deny receive_sender="org.freedesktop.System"/>
478 <deny user="john"/>
479 <deny group="enemies"/>
480 The <deny> element's attributes determine whether the deny "matches" a
483 particular action. If it matches, the action is denied (unless later
484 rules in the config file allow it).
485 send_destination and receive_sender rules mean that messages may not be
488 sent to or received from the *owner* of the given name, not that they
489 may not be sent *to that name*. That is, if a connection owns services
490 A, B, C, and sending to A is denied, sending to B or C will not work
491 either.
492 The other send_* and receive_* attributes are purely textual/by-value
495 matches against the given field in the message header.
496 "Eavesdropping" occurs when an application receives a message that was
499 explicitly addressed to a name the application does not own, or is a
500 reply to such a message. Eavesdropping thus only applies to messages
501 that are addressed to services and replies to such messages (i.e. it
502 does not apply to signals).
503 For <allow>, eavesdrop="true" indicates that the rule matches even when
506 eavesdropping. eavesdrop="false" is the default and means that the rule
507 only allows messages to go to their specified recipient. For <deny>,
508 eavesdrop="true" indicates that the rule matches only when eavesdrop‐
509 ping. eavesdrop="false" is the default for <deny> also, but here it
510 means that the rule applies always, even when not eavesdropping. The
511 eavesdrop attribute can only be combined with send and receive rules
512 (with send_* and receive_* attributes).
513 The [send|receive]_requested_reply attribute works similarly to the
517 eavesdrop attribute. It controls whether the <deny> or <allow> matches
518 a reply that is expected (corresponds to a previous method call mes‐
519 sage). This attribute only makes sense for reply messages (errors and
520 method returns), and is ignored for other message types.
521 For <allow>, [send|receive]_requested_reply="true" is the default and
524 indicates that only requested replies are allowed by the rule.
525 [send|receive]_requested_reply="false" means that the rule allows any
526 reply even if unexpected.
527 For <deny>, [send|receive]_requested_reply="false" is the default but
530 indicates that the rule matches only when the reply was not requested.
531 [send|receive]_requested_reply="true" indicates that the rule applies
532 always, regardless of pending reply state.
533 user and group denials mean that the given user or group may not con‐
536 nect to the message bus.
537 For "name", "username", "groupname", etc. the character "*" can be
540 substituted, meaning "any." Complex globs like "foo.bar.*" aren't
541 allowed for now because they'd be work to implement and maybe encourage
542 sloppy security anyway.
543 It does not make sense to deny a user or group inside a <policy> for a
546 user or group; user/group denials can only be inside context="default"
547 or context="mandatory" policies.
548 A single <deny> rule may specify combinations of attributes such as
551 send_destination and send_interface and send_type. In this case, the
552 denial applies only if both attributes match the message being denied.
553 e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
554 deny messages with the given interface AND the given bus name. To get
555 an OR effect you specify multiple <deny> rules.
556 You can't include both send_ and receive_ attributes on the same rule,
559 since "whether the message can be sent" and "whether it can be
560 received" are evaluated separately.
561 Be careful with send_interface/receive_interface, because the interface
564 field in messages is optional. In particular, do NOT specify <deny
565 send_interface="org.foo.Bar"/>! This will cause no-interface messages
566 to be blocked for all services, which is almost certainly not what you
567 intended. Always use rules of the form: <deny send_inter‐
568 face="org.foo.Bar" send_destination="org.foo.Service"/>
569 <selinux>
572 The <selinux> element contains settings related to Security Enhanced
575 Linux. More details below.
576 <associate>
579 An <associate> element appears below an <selinux> element and creates a
582 mapping. Right now only one kind of association is possible:
583 <associate own="org.freedesktop.Foobar" context="foo_t"/>
584 This means that if a connection asks to own the name "org.freedesk‐
587 top.Foobar" then the source context will be the context of the connec‐
588 tion and the target context will be "foo_t" - see the short discussion
589 of SELinux below.
590 Note, the context here is the target context when requesting a name,
593 NOT the context of the connection owning the name.
594 There's currently no way to set a default for owning any name, if we
597 add this syntax it will look like:
598 <associate own="*" context="foo_t"/>
599 If you find a reason this is useful, let the developers know. Right
600 now the default will be the security context of the bus itself.
601 If two <associate> elements specify the same name, the element appear‐
604 ing later in the configuration file will be used.
605
608 See http://www.nsa.gov/selinux/ for full details on SELinux. Some use‐
609 ful excerpts:
610 Every subject (process) and object (e.g. file, socket, IPC
613 object, etc) in the system is assigned a collection of security
614 attributes, known as a security context. A security context
615 contains all of the security attributes associated with a par‐
616 ticular subject or object that are relevant to the security
617 policy.
618 In order to better encapsulate security contexts and to provide
621 greater efficiency, the policy enforcement code of SELinux typ‐
622 ically handles security identifiers (SIDs) rather than security
623 contexts. A SID is an integer that is mapped by the security
624 server to a security context at runtime.
625 When a security decision is required, the policy enforcement
628 code passes a pair of SIDs (typically the SID of a subject and
629 the SID of an object, but sometimes a pair of subject SIDs or a
630 pair of object SIDs), and an object security class to the secu‐
631 rity server. The object security class indicates the kind of
632 object, e.g. a process, a regular file, a directory, a TCP
633 socket, etc.
634 Access decisions specify whether or not a permission is granted
637 for a given pair of SIDs and class. Each object class has a set
638 of associated permissions defined to control operations on
639 objects with that class.
640 D-Bus performs SELinux security checks in two places.
643 First, any time a message is routed from one connection to another con‐
646 nection, the bus daemon will check permissions with the security con‐
647 text of the first connection as source, security context of the second
648 connection as target, object class "dbus" and requested permission
649 "send_msg".
650 If a security context is not available for a connection (impossible
653 when using UNIX domain sockets), then the target context used is the
654 context of the bus daemon itself. There is currently no way to change
655 this default, because we're assuming that only UNIX domain sockets will
656 be used to connect to the systemwide bus. If this changes, we'll proba‐
657 bly add a way to set the default connection context.
658 Second, any time a connection asks to own a name, the bus daemon will
661 check permissions with the security context of the connection as
662 source, the security context specified for the name in the config file
663 as target, object class "dbus" and requested permission "acquire_svc".
664 The security context for a bus name is specified with the <associate>
667 element described earlier in this document. If a name has no security
668 context associated in the configuration file, the security context of
669 the bus daemon itself will be used.
670
673 If you're trying to figure out where your messages are going or why you
674 aren't getting messages, there are several things you can try.
675 Remember that the system bus is heavily locked down and if you haven't
678 installed a security policy file to allow your message through, it
679 won't work. For the session bus, this is not a concern.
680 The simplest way to figure out what's happening on the bus is to run
683 the dbus-monitor program, which comes with the D-Bus package. You can
684 also send test messages with dbus-send. These programs have their own
685 man pages.
686 If you want to know what the daemon itself is doing, you might consider
689 running a separate copy of the daemon to test against. This will allow
690 you to put the daemon under a debugger, or run it with verbose output,
691 without messing up your real session and system daemons.
692 To run a separate test copy of the daemon, for example you might open a
695 terminal and type:
696 DBUS_VERBOSE=1 dbus-daemon --session --print-address
697 The test daemon address will be printed when the daemon starts. You
700 will need to copy-and-paste this address and use it as the value of the
701 DBUS_SESSION_BUS_ADDRESS environment variable when you launch the
702 applications you want to test. This will cause those applications to
703 connect to your test bus instead of the DBUS_SESSION_BUS_ADDRESS of
704 your real session bus.
705 DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus was com‐
708 piled with verbose mode enabled. This is not recommended in production
709 builds due to performance impact. You may need to rebuild D-Bus if your
710 copy was not built with debugging in mind. (DBUS_VERBOSE also affects
711 the D-Bus library and thus applications using D-Bus; it may be useful
712 to see verbose output on both the client side and from the daemon.)
713 If you want to get fancy, you can create a custom bus configuration for
716 your test bus (see the session.conf and system.conf files that define
717 the two default configurations for example). This would allow you to
718 specify a different directory for .service files, for example.
719
723 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
724
727 Please send bug reports to the D-Bus mailing list or bug tracker, see
728 http://www.freedesktop.org/software/dbus/
729 dbus-daemon(1)