summaryrefslogtreecommitdiffstats
path: root/bus/dbus-daemon.1.in
blob: d4d816f4c616bb0007448dc9c6b057b657852da9 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
.\" 
.\" dbus-daemon manual page.
.\" Copyright (C) 2003 Red Hat, Inc.
.\"
.TH dbus-daemon 1
.SH NAME
dbus-daemon \- Message bus daemon
.SH SYNOPSIS
.PP
.B dbus-daemon
dbus-daemon [\-\-version] [\-\-session] [\-\-system] [\-\-config-file=FILE]
[\-\-print-address[=DESCRIPTOR]] [\-\-print-pid[=DESCRIPTOR]] [\-\-fork]

.SH DESCRIPTION

\fIdbus-daemon\fP is the D-Bus message bus daemon. See
http://www.freedesktop.org/software/dbus/ for more information about
the big picture. D-Bus is first a library that provides one-to-one
communication between any two applications; \fIdbus-daemon\fP is an
application that uses this library to implement a message bus
daemon. Multiple programs connect to the message bus daemon and can
exchange messages with one another.

.PP
There are two standard message bus instances: the systemwide message bus 
(installed on many systems as the "messagebus" init service) and the 
per-user-login-session message bus (started each time a user logs in).
\fIdbus-daemon\fP is used for both of these instances, but with 
a different configuration file.

.PP
The \-\-session option is equivalent to
"\-\-config-file=@EXPANDED_SYSCONFDIR@/dbus-1/session.conf" and the \-\-system
option is equivalent to
"\-\-config-file=@EXPANDED_SYSCONFDIR@/dbus-1/system.conf". By creating 
additional configuration files and using the \-\-config-file option,
additional special-purpose message bus daemons could be created.

.PP
The systemwide daemon is normally launched by an init script, 
standardly called simply "messagebus". 

.PP
The systemwide daemon is largely used for broadcasting system events, 
such as changes to the printer queue, or adding/removing devices.

.PP
The per-session daemon is used for various interprocess communication 
among desktop applications (however, it is not tied to X or the GUI 
in any way).

.PP
SIGHUP will cause the D-Bus daemon to PARTIALLY reload its
configuration file and to flush its user/group information caches. Some
configuration changes would require kicking all apps off the bus; so they will
only take effect if you restart the daemon. Policy changes should take effect
with SIGHUP.

.SH OPTIONS
The following options are supported:
.TP
.I "--config-file=FILE"
Use the given configuration file.
.TP
.I "--fork"
Force the message bus to fork and become a daemon, even if 
the configuration file does not specify that it should.
In most contexts the configuration file already gets this
right, though.
.TP
.I "--print-address[=DESCRIPTOR]"
Print the address of the message bus to standard output, or 
to the given file descriptor. This is used by programs that 
launch the message bus.
.TP
.I "--print-pid[=DESCRIPTOR]"
Print the process ID of the message bus to standard output, or 
to the given file descriptor. This is used by programs that 
launch the message bus.
.TP
.I "--session"
Use the standard configuration file for the per-login-session message
bus.
.TP
.I "--system"
Use the standard configuration file for the systemwide message bus.
.TP
.I "--version"
Print the version of the daemon.

.SH CONFIGURATION FILE

A message bus daemon has a configuration file that specializes it
for a particular application. For example, one configuration 
file might set up the message bus to be a systemwide message bus, 
while another might set it up to be a per-user-login-session bus.

.PP
The configuration file also establishes resource limits, security
parameters, and so forth.

.PP
The configuration file is not part of any interoperability
specification and its backward compatibility is not guaranteed; this
document is documentation, not specification.

.PP
The standard systemwide and per-session message bus setups are
configured in the files "@EXPANDED_SYSCONFDIR@/dbus-1/system.conf" and
"@EXPANDED_SYSCONFDIR@/dbus-1/session.conf".  These files normally
<include> a system-local.conf or session-local.conf; you can put local
overrides in those files to avoid modifying the primary configuration
files.

.PP
The configuration file is an XML document. It must have the following
doctype declaration:
.nf

   <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
    "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">

.fi

.PP
The following elements may be present in the configuration file.

.TP
.I "<busconfig>"
 
.PP
Root element.

.TP
.I "<type>"

.PP
The well-known type of the message bus. Currently known values are
"system" and "session"; if other values are set, they should be
either added to the D-Bus specification, or namespaced.  The last
<type> element "wins" (previous values are ignored).

.PP
Example: <type>session</type>

.TP
.I "<include>"
 
.PP  
Include a file <include>filename.conf</include> at this point.  If the
filename is relative, it is located relative to the configuration file
doing the including.

.PP
<include> has an optional attribute "ignore_missing=(yes|no)"
which defaults to "no" if not provided. This attribute 
controls whether it's a fatal error for the included file 
to be absent.

.TP
.I "<includedir>"

.PP
Include all files in <includedir>foo.d</includedir> at this
point. Files in the directory are included in undefined order.
Only files ending in ".conf" are included.

.PP
This is intended to allow extension of the system bus by particular
packages. For example, if CUPS wants to be able to send out
notification of printer queue changes, it could install a file to
@EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
this message and allowed the printer daemon user to send it.

.TP
.I "<user>"

.PP
The user account the daemon should run as, as either a username or a
UID. If the daemon cannot change to this UID on startup, it will exit.
If this element is not present, the daemon will not change or care
about its UID.

.PP
The last <user> entry in the file "wins", the others are ignored.

.PP
The user is changed after the bus has completed initialization.  So
sockets etc. will be created before changing user, but no data will be
read from clients before changing user. This means that sockets 
and PID files can be created in a location that requires root 
privileges for writing.

.TP
.I "<fork>"
    
.PP
If present, the bus daemon becomes a real daemon (forks 
into the background, etc.). This is generally used 
rather than the \-\-fork command line option.

.TP
.I "<listen>"

.PP
Add an address that the bus should listen on. The 
address is in the standard D-Bus format that contains 
a transport name plus possible parameters/options.

.PP
Example: <listen>unix:path=/tmp/foo</listen>

.PP
Example: <listen>tcp:host=localhost,port=1234</listen>

.PP
If there are multiple <listen> elements, then the bus listens 
on multiple addresses. The bus will pass its address to 
started services or other interested parties with 
the last address given in <listen> first. That is, 
apps will try to connect to the last <listen> address first.

.PP
A special case is using a port number of zero (or omitting the port),
which means to choose an available port selected by the operating
system. The port number chosen can be with the --print-address command
line parameter and will be present in other cases where the server 
reports its own address, such as when DBUS_SESSION_BUS_ADDRESS is set.

.PP
Example: <listen>tcp:host=localhost,port=0</listen>

.PP
tcp addresses also allow an all_interfaces=true option, which will
cause the bus to listen on all local address (INADDR_ANY) and not only
the specified host. However, the specified host will still be used as
the reported address of the server. The specified host should be a
valid name of the local machine or weird stuff will happen.

.TP
.I "<auth>"

.PP
Lists permitted authorization mechanisms. If this element doesn't
exist, then all known mechanisms are allowed.  If there are multiple
<auth> elements, all the listed mechanisms are allowed.  The order in
which mechanisms are listed is not meaningful.
    
.PP
Example: <auth>EXTERNAL</auth>

.PP
Example: <auth>DBUS_COOKIE_SHA1</auth>

.TP
.I "<servicedir>"

.PP
Adds a directory to scan for .service files. Directories are
scanned starting with the last to appear in the config file 
(the first .service file found that provides a particular 
service will be used).

.PP
Service files tell the bus how to automatically start a program.
They are primarily used with the per-user-session bus, 
not the systemwide bus.

.TP
.I "<standard_session_servicedirs/>"

.PP
<standard_session_servicedirs/> is equivalent to specifying a series
of <servicedir/> elements for each of the data directories in the "XDG
Base Directory Specification" with the subdirectory "dbus-1/services",
so for example "/usr/share/dbus-1/services" would be among the
directories searched.

.PP
The "XDG Base Directory Specification" can be found at
http://freedesktop.org/wiki/Standards/basedir-spec if it hasn't moved,
otherwise try your favorite search engine.

.PP
The <standard_session_servicedirs/> option is only relevant to the
per-user-session bus daemon defined in
@EXPANDED_SYSCONFDIR@/dbus-1/session.conf. Putting it in any other
configuration file would probably be nonsense.

.TP
.I "<standard_system_servicedirs/>"

.PP
<standard_system_servicedirs/> specifies the standard system-wide
activation directories that should be searched for service files.
This option defaults to @EXPANDED_DATADIR@/dbus-1/system-services.

.PP
The <standard_system_servicedirs/> option is only relevant to the
per-system bus daemon defined in
@EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
configuration file would probably be nonsense.

.TP
.I "<servicehelper/>"

.PP
<servicehelper/> specifies the setuid helper that is used to launch
system daemons with an alternate user. Typically this should be
the dbus-daemon-launch-helper executable in located in libexec.

.PP
The <servicehelper/> option is only relevant to the per-system bus daemon
defined in @EXPANDED_SYSCONFDIR@/dbus-1/system.conf. Putting it in any other
configuration file would probably be nonsense.

.TP
.I "<limit>"

.PP
<limit> establishes a resource limit. For example:
.nf
  <limit name="max_message_size">64</limit>
  <limit name="max_completed_connections">512</limit>
.fi

.PP
The name attribute is mandatory.
Available limit names are:
.nf
      "max_incoming_bytes"         : total size in bytes of messages
                                     incoming from a single connection
      "max_outgoing_bytes"         : total size in bytes of messages
                                     queued up for a single connection
      "max_message_size"           : max size of a single message in
                                     bytes
      "service_start_timeout"      : milliseconds (thousandths) until 
                                     a started service has to connect
      "auth_timeout"               : milliseconds (thousandths) a
                                     connection is given to
                                     authenticate
      "max_completed_connections"  : max number of authenticated connections  
      "max_incomplete_connections" : max number of unauthenticated
                                     connections
      "max_connections_per_user"   : max number of completed connections from
                                     the same user
      "max_pending_service_starts" : max number of service launches in
                                     progress at the same time
      "max_names_per_connection"   : max number of names a single 
                                     connection can own
      "max_match_rules_per_connection": max number of match rules for a single 
                                        connection
      "max_replies_per_connection" : max number of pending method 
                                     replies per connection
                                     (number of calls-in-progress)
      "reply_timeout"              : milliseconds (thousandths) 
                                     until a method call times out   
.fi

.PP
The max incoming/outgoing queue sizes allow a new message to be queued
if one byte remains below the max. So you can in fact exceed the max
by max_message_size.

.PP
max_completed_connections divided by max_connections_per_user is the
number of users that can work together to denial-of-service all other users by using
up all connections on the systemwide bus.

.PP
Limits are normally only of interest on the systemwide bus, not the user session 
buses.

.TP
.I "<policy>"

.PP
The <policy> element defines a security policy to be applied to a particular
set of connections to the bus. A policy is made up of
<allow> and <deny> elements. Policies are normally used with the systemwide bus;
they are analogous to a firewall in that they allow expected traffic 
and prevent unexpected traffic.

.PP
The <policy> element has one of three attributes:
.nf
  context="(default|mandatory)"
  user="username or userid"
  group="group name or gid"
.fi

.PP
 
Policies are applied to a connection as follows:
.nf
   - all context="default" policies are applied
   - all group="connection's user's group" policies are applied
     in undefined order
   - all user="connection's auth user" policies are applied
     in undefined order
   - all context="mandatory" policies are applied
.fi

.PP
Policies applied later will override those applied earlier, 
when the policies overlap. Multiple policies with the same 
user/group/context are applied in the order they appear 
in the config file.

.TP
.I "<deny>"
.I "<allow>"

.PP
A <deny> element appears below a <policy> element and prohibits some
action. The <allow> element makes an exception to previous <deny>
statements, and works just like <deny> but with the inverse meaning.

.PP
The possible attributes of these elements are:
.nf
   send_interface="interface_name"
   send_member="method_or_signal_name" 
   send_error="error_name" 
   send_destination="name" 
   send_type="method_call" | "method_return" | "signal" | "error" 
   send_path="/path/name"

   receive_interface="interface_name"
   receive_member="method_or_signal_name" 
   receive_error="error_name" 
   receive_sender="name" 
   receive_type="method_call" | "method_return" | "signal" | "error"
   receive_path="/path/name"

   send_requested_reply="true" | "false"
   receive_requested_reply="true" | "false"

   eavesdrop="true" | "false"

   own="name"
   user="username"
   group="groupname"
.fi

.PP
Examples:
.nf
   <deny send_interface="org.freedesktop.System" send_member="Reboot"/> 
   <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
   <deny own="org.freedesktop.System"/>
   <deny send_destination="org.freedesktop.System"/>
   <deny receive_sender="org.freedesktop.System"/>
   <deny user="john"/>
   <deny group="enemies"/>
.fi

.PP
The <deny> element's attributes determine whether the deny "matches" a
particular action. If it matches, the action is denied (unless later
rules in the config file allow it).

.PP
send_destination and receive_sender rules mean that messages may not be
sent to or received from the *owner* of the given name, not that
they may not be sent *to that name*. That is, if a connection
owns services A, B, C, and sending to A is denied, sending to B or C
will not work either.

.PP
The other send_* and receive_* attributes are purely textual/by-value
matches against the given field in the message header.

.PP
"Eavesdropping" occurs when an application receives a message that
was explicitly addressed to a name the application does not own, or
is a reply to such a message. Eavesdropping thus only applies to
messages that are addressed to services and replies to such messages
(i.e. it does not apply to signals).

.PP
For <allow>, eavesdrop="true" indicates that the rule matches even 
when eavesdropping. eavesdrop="false" is the default and means that 
the rule only allows messages to go to their specified recipient.
For <deny>, eavesdrop="true" indicates that the rule matches 
only when eavesdropping. eavesdrop="false" is the default for <deny>
also, but here it means that the rule applies always, even when 
not eavesdropping. The eavesdrop attribute can only be combined with
send and receive rules (with send_* and receive_* attributes).


.PP
The [send|receive]_requested_reply attribute works similarly to the eavesdrop
attribute. It controls whether the <deny> or <allow> matches a reply
that is expected (corresponds to a previous method call message).
This attribute only makes sense for reply messages (errors and method
returns), and is ignored for other message types.

.PP
For <allow>, [send|receive]_requested_reply="true" is the default and indicates that
only requested replies are allowed by the
rule. [send|receive]_requested_reply="false" means that the rule allows any reply
even if unexpected.

.PP
For <deny>, [send|receive]_requested_reply="false" is the default but indicates that
the rule matches only when the reply was not
requested. [send|receive]_requested_reply="true" indicates that the rule applies
always, regardless of pending reply state.

.PP
user and group denials mean that the given user or group may 
not connect to the message bus.

.PP
For "name", "username", "groupname", etc.
the character "*" can be substituted, meaning "any." Complex globs
like "foo.bar.*" aren't allowed for now because they'd be work to
implement and maybe encourage sloppy security anyway.

.PP
It does not make sense to deny a user or group inside a <policy>
for a user or group; user/group denials can only be inside
context="default" or context="mandatory" policies.

.PP
A single <deny> rule may specify combinations of attributes such as
send_destination and send_interface and send_type. In this case, the
denial applies only if both attributes match the message being denied.
e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
deny messages with the given interface AND the given bus name.
To get an OR effect you specify multiple <deny> rules.

.PP
You can't include both send_ and receive_ attributes on the same
rule, since "whether the message can be sent" and "whether it can be
received" are evaluated separately.

.PP
Be careful with send_interface/receive_interface, because the 
interface field in messages is optional.

.TP
.I "<selinux>"

.PP
The <selinux> element contains settings related to Security Enhanced Linux.
More details below.

.TP
.I "<associate>"

.PP
An <associate> element appears below an <selinux> element and
creates a mapping. Right now only one kind of association is possible:
.nf
   <associate own="org.freedesktop.Foobar" context="foo_t"/> 
.fi

.PP
This means that if a connection asks to own the name
"org.freedesktop.Foobar" then the source context will be the context
of the connection and the target context will be "foo_t" - see the 
short discussion of SELinux below.

.PP
Note, the context here is the target context when requesting a name,
NOT the context of the connection owning the name.

.PP
There's currently no way to set a default for owning any name, if
we add this syntax it will look like:
.nf
   <associate own="*" context="foo_t"/> 
.fi
If you find a reason this is useful, let the developers know.
Right now the default will be the security context of the bus itself.

.PP
If two <associate> elements specify the same name, the element
appearing later in the configuration file will be used.

.SH SELinux

.PP
See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful excerpts:

.IP "" 8
Every subject (process) and object (e.g. file, socket, IPC object,
etc) in the system is assigned a collection of security attributes,
known as a security context. A security context contains all of the
security attributes associated with a particular subject or object
that are relevant to the security policy.

.IP "" 8
In order to better encapsulate security contexts and to provide
greater efficiency, the policy enforcement code of SELinux typically
handles security identifiers (SIDs) rather than security contexts. A
SID is an integer that is mapped by the security server to a security
context at runtime.

.IP "" 8
When a security decision is required, the policy enforcement code
passes a pair of SIDs (typically the SID of a subject and the SID of
an object, but sometimes a pair of subject SIDs or a pair of object
SIDs), and an object security class to the security server. The object
security class indicates the kind of object, e.g. a process, a regular
file, a directory, a TCP socket, etc.

.IP "" 8
Access decisions specify whether or not a permission is granted for a
given pair of SIDs and class. Each object class has a set of
associated permissions defined to control operations on objects with
that class.

.PP
D-Bus performs SELinux security checks in two places.

.PP
First, any time a message is routed from one connection to another
connection, the bus daemon will check permissions with the security context of
the first connection as source, security context of the second connection
as target, object class "dbus" and requested permission "send_msg".

.PP
If a security context is not available for a connection 
(impossible when using UNIX domain sockets), then the target 
context used is the context of the bus daemon itself.
There is currently no way to change this default, because we're 
assuming that only UNIX domain sockets will be used to 
connect to the systemwide bus. If this changes, we'll 
probably add a way to set the default connection context.

.PP
Second, any time a connection asks to own a name, 
the bus daemon will check permissions with the security 
context of the connection as source, the security context specified
for the name in the config file as target, object 
class "dbus" and requested permission "acquire_svc".

.PP
The security context for a bus name is specified with the 
<associate> element described earlier in this document.
If a name has no security context associated in the 
configuration file, the security context of the bus daemon 
itself will be used.

.SH DEBUGGING

.PP
If you're trying to figure out where your messages are going or why
you aren't getting messages, there are several things you can try.

.PP
Remember that the system bus is heavily locked down and if you
haven't installed a security policy file to allow your message
through, it won't work. For the session bus, this is not a concern.

.PP
The simplest way to figure out what's happening on the bus is to run
the \fIdbus-monitor\fP program, which comes with the D-Bus
package. You can also send test messages with \fIdbus-send\fP. These
programs have their own man pages.

.PP
If you want to know what the daemon itself is doing, you might consider
running a separate copy of the daemon to test against. This will allow you 
to put the daemon under a debugger, or run it with verbose output, without 
messing up your real session and system daemons.

.PP
To run a separate test copy of the daemon, for example you might open a terminal 
and type: 
.nf
  DBUS_VERBOSE=1 dbus-daemon --session --print-address
.fi

.PP
The test daemon address will be printed when the daemon starts. You will need
to copy-and-paste this address and use it as the value of the 
DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications
you want to test. This will cause those applications to connect to your 
test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.

.PP
DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus
was compiled with verbose mode enabled. This is not recommended in
production builds due to performance impact. You may need to rebuild
D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
also affects the D-Bus library and thus applications using D-Bus; it may 
be useful to see verbose output on both the client side and from the daemon.)

.PP
If you want to get fancy, you can create a custom bus
configuration for your test bus (see the session.conf and system.conf
files that define the two default configurations for example). This
would allow you to specify a different directory for .service files,
for example.


.SH AUTHOR
See http://www.freedesktop.org/software/dbus/doc/AUTHORS

.SH BUGS
Please send bug reports to the D-Bus mailing list or bug tracker,
see http://www.freedesktop.org/software/dbus/