1DBUS-DAEMON(1)                   User Commands                  DBUS-DAEMON(1)
2
3
4

NAME

6       dbus-daemon - Message bus daemon
7

SYNOPSIS

9       dbus-daemon
10
11       dbus-daemon [--version] [--session] [--system] [--config-file=FILE]
12                   [--print-address [=DESCRIPTOR]] [--print-pid [=DESCRIPTOR]]
13                   [--fork] [--nosyslog] [--syslog] [--syslog-only]
14                   [--ready-event-handle=value]
15
16

DESCRIPTION

18       dbus-daemon is the D-Bus message bus daemon. See
19       http://www.freedesktop.org/software/dbus/ for more information about
20       the big picture. D-Bus is first a library that provides one-to-one
21       communication between any two applications; dbus-daemon is an
22       application that uses this library to implement a message bus daemon.
23       Multiple programs connect to the message bus daemon and can exchange
24       messages with one another.
25
26       There are two standard message bus instances: the systemwide message
27       bus (installed on many systems as the "messagebus" init service) and
28       the per-user-login-session message bus (started each time a user logs
29       in).  dbus-daemon is used for both of these instances, but with a
30       different configuration file.
31
32       The --session option is equivalent to
33       "--config-file=/usr/share/dbus-1/session.conf" and the --system option
34       is equivalent to "--config-file=/usr/share/dbus-1/system.conf". By
35       creating additional configuration files and using the --config-file
36       option, additional special-purpose message bus daemons could be
37       created.
38
39       The systemwide daemon is normally launched by an init script,
40       standardly called simply "messagebus".
41
42       The systemwide daemon is largely used for broadcasting system events,
43       such as changes to the printer queue, or adding/removing devices.
44
45       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
49       SIGHUP will cause the D-Bus daemon to PARTIALLY reload its
50       configuration file and to flush its user/group information caches. Some
51       configuration changes would require kicking all apps off the bus; so
52       they will only take effect if you restart the daemon. Policy changes
53       should take effect with SIGHUP.
54

OPTIONS

56       The following options are supported:
57
58       --config-file=FILE
59           Use the given configuration file.
60
61       --fork
62           Force the message bus to fork and become a daemon, even if the
63           configuration file does not specify that it should. In most
64           contexts the configuration file already gets this right, though.
65           This option is not supported on Windows.
66
67       --nofork
68           Force the message bus not to fork and become a daemon, even if the
69           configuration file specifies that it should. On Windows, the
70           dbus-daemon never forks, so this option is allowed but does
71           nothing.
72
73       --print-address[=DESCRIPTOR]
74           Print the address of the message bus to standard output, or to the
75           given file descriptor. This is used by programs that launch the
76           message bus.
77
78       --print-pid[=DESCRIPTOR]
79           Print the process ID of the message bus to standard output, or to
80           the given file descriptor. This is used by programs that launch the
81           message bus.
82
83       --session
84           Use the standard configuration file for the per-login-session
85           message bus.
86
87       --system
88           Use the standard configuration file for the systemwide message bus.
89
90       --version
91           Print the version of the daemon.
92
93       --introspect
94           Print the introspection information for all D-Bus internal
95           interfaces.
96
97       --address[=ADDRESS]
98           Set the address to listen on. This option overrides the address
99           configured in the configuration file via the <listen> directive.
100           See the documentation of that directive for more details.
101
102       --systemd-activation
103           Enable systemd-style service activation. Only useful in conjunction
104           with the systemd system and session manager on Linux.
105
106       --nopidfile
107           Don't write a PID file even if one is configured in the
108           configuration files.
109
110       --syslog
111           Force the message bus to use the system log for messages, in
112           addition to writing to standard error, even if the configuration
113           file does not specify that it should. On Unix, this uses the
114           syslog; on Windows, this uses OutputDebugString().
115
116       --syslog-only
117           Force the message bus to use the system log for messages, and not
118           duplicate them to standard error. On Unix, this uses the syslog; on
119           Windows, this uses OutputDebugString().
120
121       --nosyslog
122           Force the message bus to use only standard error for messages, even
123           if the configuration file specifies that it should use the system
124           log.
125
126       --ready-event-handle=value
127           With this option, the dbus daemon raises an event when it is ready
128           to process connections. The handle must be the Windows handle for
129           an event object, in the format printed by the printf format string
130           %p. The parent process must create this event object (for example
131           with the CreateEvent function) in a nonsignaled state, then
132           configure it to be inherited by the dbus-daemon process. The
133           dbus-daemon will signal the event as if via SetEvent when it is
134           ready to receive connections from clients. The parent process can
135           wait for this to occur by using functions such as
136           WaitForSingleObject. This option is only supported under Windows.
137           On Unix platforms, a similar result can be achieved by waiting for
138           the address and/or process ID to be printed to the inherited file
139           descriptors used for --print-address and/or --print-pid.
140

CONFIGURATION FILE

142       A message bus daemon has a configuration file that specializes it for a
143       particular application. For example, one configuration file might set
144       up the message bus to be a systemwide message bus, while another might
145       set it up to be a per-user-login-session bus.
146
147       The configuration file also establishes resource limits, security
148       parameters, and so forth.
149
150       The configuration file is not part of any interoperability
151       specification and its backward compatibility is not guaranteed; this
152       document is documentation, not specification.
153
154       The standard systemwide and per-session message bus setups are
155       configured in the files "/usr/share/dbus-1/system.conf" and
156       "/usr/share/dbus-1/session.conf". These files normally <include> a
157       system-local.conf or session-local.conf in /etc/dbus-1; you can put
158       local overrides in those files to avoid modifying the primary
159       configuration files.
160
161       The standard system bus normally reads additional XML files from
162       /usr/share/dbus-1/system.d. Third-party packages should install the
163       default policies necessary for correct operation into that directory,
164       which has been supported since dbus 1.10 (released in 2015).
165
166       The standard system bus normally also reads XML files from
167       /etc/dbus-1/system.d, which should be used by system administrators if
168       they wish to override default policies.
169
170       Third-party packages would historically install XML files into
171       /etc/dbus-1/system.d, but this practice is now considered to be
172       deprecated: that directory should be treated as reserved for the system
173       administrator.
174
175       The configuration file is an XML document. It must have the following
176       doctype declaration:
177
178
179              <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
180               "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
181
182
183       The following elements may be present in the configuration file.
184
185<busconfig>
186
187       Root element.
188
189<type>
190
191       The well-known type of the message bus. Currently known values are
192       "system" and "session"; if other values are set, they should be either
193       added to the D-Bus specification, or namespaced. The last <type>
194       element "wins" (previous values are ignored). This element only
195       controls which message bus specific environment variables are set in
196       activated clients. Most of the policy that distinguishes a session bus
197       from the system bus is controlled from the other elements in the
198       configuration file.
199
200       If the well-known type of the message bus is "session", then the
201       DBUS_STARTER_BUS_TYPE environment variable will be set to "session" and
202       the DBUS_SESSION_BUS_ADDRESS environment variable will be set to the
203       address of the session bus. Likewise, if the type of the message bus is
204       "system", then the DBUS_STARTER_BUS_TYPE environment variable will be
205       set to "system" and the DBUS_SYSTEM_BUS_ADDRESS environment variable
206       will be set to the address of the system bus (which is normally well
207       known anyway).
208
209       Example: <type>session</type>
210
211<include>
212
213       Include a file <include>filename.conf</include> at this point. If the
214       filename is relative, it is located relative to the configuration file
215       doing the including.
216
217       <include> has an optional attribute "ignore_missing=(yes|no)" which
218       defaults to "no" if not provided. This attribute controls whether it's
219       a fatal error for the included file to be absent.
220
221<includedir>
222
223       Include all files in <includedir>foo.d</includedir> at this point.
224       Files in the directory are included in undefined order. Only files
225       ending in ".conf" are included.
226
227       This is intended to allow extension of the system bus by particular
228       packages. For example, if CUPS wants to be able to send out
229       notification of printer queue changes, it could install a file to
230       /usr/share/dbus-1/system.d that allowed all apps to receive this
231       message and allowed the printer daemon user to send it.
232
233<user>
234
235       The user account the daemon should run as, as either a username or a
236       UID. If the daemon cannot change to this UID on startup, it will exit.
237       If this element is not present, the daemon will not change or care
238       about its UID.
239
240       The last <user> entry in the file "wins", the others are ignored.
241
242       The user is changed after the bus has completed initialization. So
243       sockets etc. will be created before changing user, but no data will be
244       read from clients before changing user. This means that sockets and PID
245       files can be created in a location that requires root privileges for
246       writing.
247
248<fork>
249
250       If present, the bus daemon becomes a real daemon (forks into the
251       background, etc.). This is generally used rather than the --fork
252       command line option.
253
254<keep_umask>
255
256       If present, the bus daemon keeps its original umask when forking. This
257       may be useful to avoid affecting the behavior of child processes.
258
259<syslog>
260
261       If present, the bus daemon will log to syslog. The --syslog,
262       --syslog-only and --nosyslog command-line options take precedence over
263       this setting.
264
265<pidfile>
266
267       If present, the bus daemon will write its pid to the specified file.
268       The --nopidfile command-line option takes precedence over this setting.
269
270<allow_anonymous>
271
272       If present, connections that authenticated using the ANONYMOUS
273       mechanism will be authorized to connect. This option has no practical
274       effect unless the ANONYMOUS mechanism has also been enabled using the
275       <auth> element, described below.
276
277       Using this directive in the configuration of the well-known system bus
278       or the well-known session bus will make that bus insecure and should
279       never be done. Similarly, on custom bus types, using this directive
280       will usually make the custom bus insecure, unless its configuration has
281       been specifically designed to prevent anonymous users from causing
282       damage or escalating privileges.
283
284<listen>
285
286       Add an address that the bus should listen on. The address is in the
287       standard D-Bus format that contains a transport name plus possible
288       parameters/options.
289
290       On platforms other than Windows, unix-based transports (unix, systemd,
291       launchd) are the default for both the well-known system bus and the
292       well-known session bus, and are strongly recommended.
293
294       On Windows, unix-based transports are not available, so TCP-based
295       transports must be used. Similar to remote X11, the tcp and nonce-tcp
296       transports have no integrity or confidentiality protection, so they
297       should normally only be used across the local loopback interface, for
298       example using an address like tcp:host=127.0.0.1 or
299       nonce-tcp:host=localhost. In particular, configuring the well-known
300       system bus or the well-known session bus to listen on a non-loopback
301       TCP address is insecure.
302
303       Developers are sometimes tempted to use remote TCP as a debugging tool.
304       However, if this functionality is left enabled in finished products,
305       the result will be dangerously insecure. Instead of using remote TCP,
306       developers should relay connections via Secure Shell or a similar
307       protocol[1].
308
309       Remote TCP connections were historically sometimes used to share a
310       single session bus between login sessions of the same user on different
311       machines within a trusted local area network, in conjunction with
312       unencrypted remote X11, a NFS-shared home directory and NIS (YP)
313       authentication. This is insecure against an attacker on the same LAN
314       and should be considered strongly deprecated; more specifically, it is
315       insecure in the same ways and for the same reasons as unencrypted
316       remote X11 and NFSv2/NFSv3. The D-Bus maintainers recommend using a
317       separate session bus per (user, machine) pair, only accessible from
318       within that machine.
319
320       Example: <listen>unix:path=/tmp/foo</listen>
321
322       Example: <listen>tcp:host=localhost,port=1234</listen>
323
324       If there are multiple <listen> elements, then the bus listens on
325       multiple addresses. The bus will pass its address to started services
326       or other interested parties with the last address given in <listen>
327       first. That is, apps will try to connect to the last <listen> address
328       first.
329
330       tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames. If
331       a hostname resolves to multiple addresses, the server will bind to all
332       of them. The family=ipv4 or family=ipv6 options can be used to force it
333       to bind to a subset of addresses
334
335       Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen>
336
337       A special case is using a port number of zero (or omitting the port),
338       which means to choose an available port selected by the operating
339       system. The port number chosen can be obtained with the --print-address
340       command line parameter and will be present in other cases where the
341       server reports its own address, such as when DBUS_SESSION_BUS_ADDRESS
342       is set.
343
344       Example: <listen>tcp:host=localhost,port=0</listen>
345
346       tcp/nonce-tcp addresses also allow a bind=hostname option, used in a
347       listenable address to configure the interface on which the server will
348       listen: either the hostname is the IP address of one of the local
349       machine's interfaces (most commonly 127.0.0.1), a DNS name that
350       resolves to one of those IP addresses, '0.0.0.0' to listen on all IPv4
351       interfaces simultaneously, or '::' to listen on all IPv4 and IPv6
352       interfaces simultaneously (if supported by the OS). If not specified,
353       the default is the same value as "host".
354
355       Example: <listen>tcp:host=localhost,bind=0.0.0.0,port=0</listen>
356
357<auth>
358
359       Lists permitted authorization mechanisms. If this element doesn't
360       exist, then all known mechanisms are allowed. If there are multiple
361       <auth> elements, all the listed mechanisms are allowed. The order in
362       which mechanisms are listed is not meaningful.
363
364       On non-Windows operating systems, allowing only the EXTERNAL
365       authentication mechanism is strongly recommended. This is the default
366       for the well-known system bus and for the well-known session bus.
367
368       Example: <auth>EXTERNAL</auth>
369
370       Example: <auth>DBUS_COOKIE_SHA1</auth>
371
372<servicedir>
373
374       Adds a directory to search for .service files, which tell the
375       dbus-daemon how to start a program to provide a particular well-known
376       bus name. See the D-Bus Specification for more details about the
377       contents of .service files.
378
379       If a particular service is found in more than one <servicedir>, the
380       first directory listed in the configuration file takes precedence. If
381       two service files providing the same well-known bus name are found in
382       the same directory, it is arbitrary which one will be chosen (this can
383       only happen if at least one of the service files does not have the
384       recommended name, which is its well-known bus name followed by
385       ".service").
386
387<standard_session_servicedirs/>
388
389       <standard_session_servicedirs/> requests a standard set of session
390       service directories. Its effect is similar to specifying a series of
391       <servicedir/> elements for each of the data directories, in the order
392       given here. It is not exactly equivalent, because there is currently no
393       way to disable directory monitoring or enforce strict service file
394       naming for a <servicedir/>.
395
396       As with <servicedir/> elements, if a particular service is found in
397       more than one service directory, the first directory takes precedence.
398       If two service files providing the same well-known bus name are found
399       in the same directory, it is arbitrary which one will be chosen (this
400       can only happen if at least one of the service files does not have the
401       recommended name, which is its well-known bus name followed by
402       ".service").
403
404       On Unix, the standard session service directories are:
405
406$XDG_RUNTIME_DIR/dbus-1/services, if XDG_RUNTIME_DIR is set (see
407           the XDG Base Directory Specification for details of
408           XDG_RUNTIME_DIR): this location is suitable for transient services
409           created at runtime by systemd generators (see
410           systemd.generator(7)), session managers or other session
411           infrastructure. It is an extension provided by the reference
412           implementation of dbus-daemon, and is not standardized in the D-Bus
413           Specification.
414
415           Unlike the other standard session service directories, this
416           directory enforces strict naming for the service files: the
417           filename must be exactly the well-known bus name of the service,
418           followed by ".service".
419
420           Also unlike the other standard session service directories, this
421           directory is never monitored with inotify(7) or similar APIs.
422           Programs that create service files in this directory while a
423           dbus-daemon is running are expected to call the dbus-daemon's
424           ReloadConfig() method after they have made changes.
425
426$XDG_DATA_HOME/dbus-1/services, where XDG_DATA_HOME defaults to
427           ~/.local/share (see the XDG Base Directory Specification): this
428           location is specified by the D-Bus Specification, and is suitable
429           for per-user, locally-installed software.
430
431directory/dbus-1/services for each directory in XDG_DATA_DIRS,
432           where XDG_DATA_DIRS defaults to /usr/local/share:/usr/share (see
433           the XDG Base Directory Specification): these locations are
434           specified by the D-Bus Specification. The defaults are suitable for
435           software installed locally by a system administrator
436           (/usr/local/share) or for software installed from operating system
437           packages (/usr/share). Per-user or system-wide configuration that
438           sets the XDG_DATA_DIRS environment variable can extend this search
439           path to cover installations in other locations, for example
440           ~/.local/share/flatpak/exports/share/ and
441           /var/lib/flatpak/exports/share/ when flatpak(1) is used.
442
443${datadir}/dbus-1/services for the ${datadir} that was specified
444           when dbus was compiled, typically /usr/share: this location is an
445           extension provided by the reference dbus-daemon implementation, and
446           is suitable for software stacks installed alongside dbus-daemon.
447
448       The "XDG Base Directory Specification" can be found at
449       http://freedesktop.org/wiki/Standards/basedir-spec if it hasn't moved,
450       otherwise try your favorite search engine.
451
452       On Windows, the standard session service directories are:
453
454%CommonProgramFiles%/dbus-1/services if %CommonProgramFiles% is
455           set: this location is suitable for system-wide installed software
456           packages
457
458       •   A share/dbus-1/services directory found in the same directory
459           hierarchy (prefix) as the dbus-daemon: this location is suitable
460           for software stacks installed alongside dbus-daemon
461
462       The <standard_session_servicedirs/> option is only relevant to the
463       per-user-session bus daemon defined in /etc/dbus-1/session.conf.
464       Putting it in any other configuration file would probably be nonsense.
465
466<standard_system_servicedirs/>
467
468       <standard_system_servicedirs/> specifies the standard system-wide
469       activation directories that should be searched for service files. As
470       with session services, the first directory listed has highest
471       precedence.
472
473       On Unix, the standard system service directories are:
474
475       •   /usr/local/share/dbus-1/system-services: this location is specified
476           by the D-Bus Specification, and is suitable for software installed
477           locally by the system administrator
478
479       •   /usr/share/dbus-1/system-services: this location is specified by
480           the D-Bus Specification, and is suitable for software installed by
481           operating system packages
482
483${datadir}/dbus-1/system-services for the ${datadir} that was
484           specified when dbus was compiled, typically /usr/share: this
485           location is an extension provided by the reference dbus-daemon
486           implementation, and is suitable for software stacks installed
487           alongside dbus-daemon
488
489       •   /lib/dbus-1/system-services: this location is specified by the
490           D-Bus Specification, and was intended for software installed by
491           operating system packages and used during early boot (but it should
492           be considered deprecated, because the reference dbus-daemon is not
493           designed to be available during early boot)
494
495       On Windows, there is no standard system bus, so there are no standard
496       system bus directories either.
497
498       The <standard_system_servicedirs/> option is only relevant to the
499       per-system bus daemon defined in /usr/share/dbus-1/system.conf. Putting
500       it in any other configuration file would probably be nonsense.
501
502<servicehelper/>
503
504       <servicehelper/> specifies the setuid helper that is used to launch
505       system daemons with an alternate user. Typically this should be the
506       dbus-daemon-launch-helper executable in located in libexec.
507
508       The <servicehelper/> option is only relevant to the per-system bus
509       daemon defined in /usr/share/dbus-1/system.conf. Putting it in any
510       other configuration file would probably be nonsense.
511
512<limit>
513
514       <limit> establishes a resource limit. For example:
515
516             <limit name="max_message_size">64</limit>
517             <limit name="max_completed_connections">512</limit>
518
519       The name attribute is mandatory. Available limit names are:
520
521                 "max_incoming_bytes"         : total size in bytes of messages
522                                                incoming from a single connection
523                 "max_incoming_unix_fds"      : total number of unix fds of messages
524                                                incoming from a single connection
525                 "max_outgoing_bytes"         : total size in bytes of messages
526                                                queued up for a single connection
527                 "max_outgoing_unix_fds"      : total number of unix fds of messages
528                                                queued up for a single connection
529                 "max_message_size"           : max size of a single message in
530                                                bytes
531                 "max_message_unix_fds"       : max unix fds of a single message
532                 "service_start_timeout"      : milliseconds (thousandths) until
533                                                a started service has to connect
534                 "auth_timeout"               : milliseconds (thousandths) a
535                                                connection is given to
536                                                authenticate
537                 "pending_fd_timeout"         : milliseconds (thousandths) a
538                                                fd is given to be transmitted to
539                                                dbus-daemon before disconnecting the
540                                                connection
541                 "max_completed_connections"  : max number of authenticated connections
542                 "max_incomplete_connections" : max number of unauthenticated
543                                                connections
544                 "max_connections_per_user"   : max number of completed connections from
545                                                the same user (only enforced on Unix OSs)
546                 "max_pending_service_starts" : max number of service launches in
547                                                progress at the same time
548                 "max_names_per_connection"   : max number of names a single
549                                                connection can own
550                 "max_match_rules_per_connection": max number of match rules for a single
551                                                   connection
552                 "max_replies_per_connection" : max number of pending method
553                                                replies per connection
554                                                (number of calls-in-progress)
555                 "reply_timeout"              : milliseconds (thousandths)
556                                                until a method call times out
557
558       The max incoming/outgoing queue sizes allow a new message to be queued
559       if one byte remains below the max. So you can in fact exceed the max by
560       max_message_size.
561
562       max_completed_connections divided by max_connections_per_user is the
563       number of users that can work together to denial-of-service all other
564       users by using up all connections on the systemwide bus.
565
566       Limits are normally only of interest on the systemwide bus, not the
567       user session buses.
568
569<policy>
570
571       The <policy> element defines a security policy to be applied to a
572       particular set of connections to the bus. A policy is made up of
573       <allow> and <deny> elements. Policies are normally used with the
574       systemwide bus; they are analogous to a firewall in that they allow
575       expected traffic and prevent unexpected traffic.
576
577       Currently, the system bus has a default-deny policy for sending method
578       calls and owning bus names, and a default-allow policy for receiving
579       messages, sending signals, and sending a single success or error reply
580       for each method call that does not have the NO_REPLY flag. Sending more
581       than the expected number of replies is not allowed.
582
583       In general, it is best to keep system services as small, targeted
584       programs which run in their own process and provide a single bus name.
585       Then, all that is needed is an <allow> rule for the "own" permission to
586       let the process claim the bus name, and a "send_destination" rule to
587       allow traffic from some or all uids to your service.
588
589       The <policy> element has one of four attributes:
590
591             context="(default|mandatory)"
592             at_console="(true|false)"
593             user="username or userid"
594             group="group name or gid"
595
596       Policies are applied to a connection as follows:
597
598              - all context="default" policies are applied
599              - all group="connection's user's group" policies are applied
600                in undefined order
601              - all user="connection's auth user" policies are applied
602                in undefined order
603              - all at_console="true" policies are applied
604              - all at_console="false" policies are applied
605              - all context="mandatory" policies are applied
606
607       Policies applied later will override those applied earlier, when the
608       policies overlap. Multiple policies with the same user/group/context
609       are applied in the order they appear in the config file.
610
611       <deny>
612           <allow>
613
614       A <deny> element appears below a <policy> element and prohibits some
615       action. The <allow> element makes an exception to previous <deny>
616       statements, and works just like <deny> but with the inverse meaning.
617
618       The possible attributes of these elements are:
619
620              send_interface="interface_name" | "*"
621              send_member="method_or_signal_name" | "*"
622              send_error="error_name" | "*"
623              send_broadcast="true" | "false"
624              send_destination="name" | "*"
625              send_destination_prefix="name"
626              send_type="method_call" | "method_return" | "signal" | "error" | "*"
627              send_path="/path/name" | "*"
628
629              receive_interface="interface_name" | "*"
630              receive_member="method_or_signal_name" | "*"
631              receive_error="error_name" | "*"
632              receive_sender="name" | "*"
633              receive_type="method_call" | "method_return" | "signal" | "error" | "*"
634              receive_path="/path/name" | "*"
635
636              send_requested_reply="true" | "false"
637              receive_requested_reply="true" | "false"
638
639              eavesdrop="true" | "false"
640
641              own="name" | "*"
642              own_prefix="name"
643              user="username" | "*"
644              group="groupname" | "*"
645
646       Examples:
647
648              <deny send_destination="org.freedesktop.Service" send_interface="org.freedesktop.System" send_member="Reboot"/>
649              <deny send_destination="org.freedesktop.System"/>
650              <deny receive_sender="org.freedesktop.System"/>
651              <deny user="john"/>
652              <deny group="enemies"/>
653
654       The <deny> element's attributes determine whether the deny "matches" a
655       particular action. If it matches, the action is denied (unless later
656       rules in the config file allow it).
657
658       Rules with one or more of the send_* family of attributes are checked
659       in order when a connection attempts to send a message. The last rule
660       that matches the message determines whether it may be sent. The
661       well-known session bus normally allows sending any message. The
662       well-known system bus normally allows sending any signal, selected
663       method calls to the dbus-daemon, and exactly one reply to each
664       previously-sent method call (either success or an error). Either of
665       these can be overridden by configuration; on the system bus, services
666       that will receive method calls must install configuration that allows
667       them to do so, usually via rules of the form <policy
668       context="default"><allow send_destination="..."/><policy>.
669
670       Rules with one or more of the receive_* family of attributes, or with
671       the eavesdrop attribute and no others, are checked for each recipient
672       of a message (there might be more than one recipient if the message is
673       a broadcast or a connection is eavesdropping). The last rule that
674       matches the message determines whether it may be received. The
675       well-known session bus normally allows receiving any message, including
676       eavesdropping. The well-known system bus normally allows receiving any
677       message that was not eavesdropped (any unicast message addressed to the
678       recipient, and any broadcast message).
679
680       The eavesdrop, min_fds and max_fds attributes are modifiers that can be
681       applied to either send_* or receive_* rules, and are documented below.
682
683       send_destination and receive_sender rules mean that messages may not be
684       sent to or received from the *owner* of the given name, not that they
685       may not be sent *to that name*. That is, if a connection owns services
686       A, B, C, and sending to A is denied, sending to B or C will not work
687       either. As a special case, send_destination="*" matches any message
688       (whether it has a destination specified or not), and receive_sender="*"
689       similarly matches any message.
690
691       A send_destination_prefix rule opens or closes the whole namespace for
692       sending. It means that messages may or may not be sent to the owner of
693       any name matching the prefix, regardless of whether it is the primary
694       or the queued owner. In other words, for <allow
695       send_destination_prefix="a.b"/> rule and names "a.b", "a.b.c", and
696       "a.b.c.d" present on the bus, it works the same as if three separate
697       rules: <allow send_destination="a.b"/>, <allow
698       send_destination="a.b.c"/>, and <allow send_destination="a.b.c.d"/> had
699       been defined. The rules for matching names are the same as in
700       own_prefix (see below): a prefix of "a.b" matches names "a.b" or
701       "a.b.c" or "a.b.c.d", but not "a.bc" or "a.c". The
702       send_destination_prefix attribute cannot be combined with the
703       send_destination attribute in the same rule.
704
705       Rules with send_broadcast="true" match signal messages with no
706       destination (broadcasts). Rules with send_broadcast="false" are the
707       inverse: they match any unicast destination (unicast signals, together
708       with all method calls, replies and errors) but do not match messages
709       with no destination (broadcasts). This is not the same as
710       send_destination="*", which matches any sent message, regardless of
711       whether it has a destination or not.
712
713       The other send_* and receive_* attributes are purely textual/by-value
714       matches against the given field in the message header, except that for
715       the attributes where it is allowed, * matches any message (whether it
716       has the relevant header field or not). For example, send_interface="*"
717       matches any sent message, even if it does not contain an interface
718       header field. More complex glob matching such as foo.bar.*  is not
719       allowed.
720
721       "Eavesdropping" occurs when an application receives a message that was
722       explicitly addressed to a name the application does not own, or is a
723       reply to such a message. Eavesdropping thus only applies to messages
724       that are addressed to services and replies to such messages (i.e. it
725       does not apply to signals).
726
727       For <allow>, eavesdrop="true" indicates that the rule matches even when
728       eavesdropping. eavesdrop="false" is the default and means that the rule
729       only allows messages to go to their specified recipient. For <deny>,
730       eavesdrop="true" indicates that the rule matches only when
731       eavesdropping. eavesdrop="false" is the default for <deny> also, but
732       here it means that the rule applies always, even when not
733       eavesdropping. The eavesdrop attribute can only be combined with send
734       and receive rules (with send_* and receive_* attributes).
735
736       The [send|receive]_requested_reply attribute works similarly to the
737       eavesdrop attribute. It controls whether the <deny> or <allow> matches
738       a reply that is expected (corresponds to a previous method call
739       message). This attribute only makes sense for reply messages (errors
740       and method returns), and is ignored for other message types.
741
742       For <allow>, [send|receive]_requested_reply="true" is the default and
743       indicates that only requested replies are allowed by the rule.
744       [send|receive]_requested_reply="false" means that the rule allows any
745       reply even if unexpected.
746
747       For <deny>, [send|receive]_requested_reply="false" is the default but
748       indicates that the rule matches only when the reply was not requested.
749       [send|receive]_requested_reply="true" indicates that the rule applies
750       always, regardless of pending reply state.
751
752       The min_fds and max_fds attributes modify either send_* or receive_*
753       rules. A rule with the min_fds attribute only matches messages if they
754       have at least that many Unix file descriptors attached. Conversely, a
755       rule with the max_fds attribute only matches messages if they have no
756       more than that many file descriptors attached. In practice, rules with
757       these attributes will most commonly take the form <allow
758       send_destination="..." max_fds="0"/>, <deny send_destination="..."
759       min_fds="1"/> or <deny receive_sender="*" min_fds="1"/>.
760
761       Rules with the user or group attribute are checked when a new
762       connection to the message bus is established, and control whether the
763       connection can continue. Each of these attributes cannot be combined
764       with any other attribute. As a special case, both user="*" and
765       group="*" match any connection. If there are no rules of this form, the
766       default is to allow connections from the same user ID that owns the
767       dbus-daemon process. The well-known session bus normally uses that
768       default behaviour, while the well-known system bus normally allows any
769       connection.
770
771       Rules with the own or own_prefix attribute are checked when a
772       connection attempts to own a well-known bus names. As a special case,
773       own="*" matches any well-known bus name. The well-known session bus
774       normally allows any connection to own any name, while the well-known
775       system bus normally does not allow any connection to own any name,
776       except where allowed by further configuration. System services that
777       will own a name must install configuration that allows them to do so,
778       usually via rules of the form <policy user="some-system-user"><allow
779       own="..."/></policy>.
780
781       <allow own_prefix="a.b"/> allows you to own the name "a.b" or any name
782       whose first dot-separated elements are "a.b": in particular, you can
783       own "a.b.c" or "a.b.c.d", but not "a.bc" or "a.c". This is useful when
784       services like Telepathy and ReserveDevice define a meaning for subtrees
785       of well-known names, such as
786       org.freedesktop.Telepathy.ConnectionManager.(anything) and
787       org.freedesktop.ReserveDevice1.(anything).
788
789       It does not make sense to deny a user or group inside a <policy> for a
790       user or group; user/group denials can only be inside context="default"
791       or context="mandatory" policies.
792
793       A single <deny> rule may specify combinations of attributes such as
794       send_destination and send_interface and send_type. In this case, the
795       denial applies only if both attributes match the message being denied.
796       e.g. <deny send_interface="foo.bar" send_destination="foo.blah"/> would
797       deny messages with the given interface AND the given bus name. To get
798       an OR effect you specify multiple <deny> rules.
799
800       You can't include both send_ and receive_ attributes on the same rule,
801       since "whether the message can be sent" and "whether it can be
802       received" are evaluated separately.
803
804       Be careful with send_interface/receive_interface, because the interface
805       field in messages is optional. In particular, do NOT specify <deny
806       send_interface="org.foo.Bar"/>! This will cause no-interface messages
807       to be blocked for all services, which is almost certainly not what you
808       intended. Always use rules of the form: <deny
809       send_interface="org.foo.Bar" send_destination="org.foo.Service"/>
810
811<selinux>
812
813       The <selinux> element contains settings related to Security Enhanced
814       Linux. More details below.
815
816<associate>
817
818       An <associate> element appears below an <selinux> element and creates a
819       mapping. Right now only one kind of association is possible:
820
821              <associate own="org.freedesktop.Foobar" context="foo_t"/>
822
823       This means that if a connection asks to own the name
824       "org.freedesktop.Foobar" then the source context will be the context of
825       the connection and the target context will be "foo_t" - see the short
826       discussion of SELinux below.
827
828       Note, the context here is the target context when requesting a name,
829       NOT the context of the connection owning the name.
830
831       There's currently no way to set a default for owning any name, if we
832       add this syntax it will look like:
833
834              <associate own="*" context="foo_t"/>
835
836       If you find a reason this is useful, let the developers know. Right now
837       the default will be the security context of the bus itself.
838
839       If two <associate> elements specify the same name, the element
840       appearing later in the configuration file will be used.
841
842<apparmor>
843
844       The <apparmor> element is used to configure AppArmor mediation on the
845       bus. It can contain one attribute that specifies the mediation mode:
846
847              <apparmor mode="(enabled|disabled|required)"/>
848
849       The default mode is "enabled". In "enabled" mode, AppArmor mediation
850       will be performed if AppArmor support is available in the kernel. If it
851       is not available, dbus-daemon will start but AppArmor mediation will
852       not occur. In "disabled" mode, AppArmor mediation is disabled. In
853       "required" mode, AppArmor mediation will be enabled if AppArmor support
854       is available, otherwise dbus-daemon will refuse to start.
855
856       The AppArmor mediation mode of the bus cannot be changed after the bus
857       starts. Modifying the mode in the configuration file and sending a
858       SIGHUP signal to the daemon has no effect on the mediation mode.
859

INTEGRATING SESSION SERVICES

861       Integration files are not mandatory for session services: any program
862       with access to the session bus can request a well-known name and
863       provide D-Bus interfaces.
864
865       Many D-Bus session services support service activation, a mechanism in
866       which the dbus-daemon can launch the service on-demand, either by
867       running the session service itself or by communicating with systemd
868       --user. This is set up by creating a service file in the directory
869       ${datadir}/dbus-1/services, for example:
870
871           [D-BUS Service]
872           Name=com.example.SessionService1
873           Exec=/usr/bin/example-session-service
874           # Optional
875           SystemdService=example-session-service
876
877       See the D-Bus Specification[2] for details of the contents and
878       interpretation of service files.
879
880       If there is a service file for com.example.SessionService1, it should
881       be named com.example.SessionService1.service, although for
882       compatibility with legacy services this is not mandatory.
883
884       Session services that declare the optional SystemdService must also
885       provide a systemd user service unit file whose name or Alias matches
886       the SystemdService (see systemd.unit(5), systemd.service(5) for further
887       details on systemd service units), for example:
888
889           [Unit]
890           Description=Example session service
891
892           [Service]
893           Type=dbus
894           BusName=com.example.SessionService1
895           ExecStart=/usr/bin/example-session-service
896
897

INTEGRATING SYSTEM SERVICES

899       The standard system bus does not allow method calls or owning
900       well-known bus names by default, so a useful D-Bus system service will
901       normally need to configure a default security policy that allows it to
902       work. D-Bus system services should install a default policy file in
903       ${datadir}/dbus-1/service.d, containing the policy rules necessary to
904       make that system service functional. A best-practice policy file will
905       often look like this:
906
907           <?xml version="1.0" encoding="UTF-8"?>
908           <!DOCTYPE busconfig PUBLIC
909            "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
910            "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
911           <busconfig>
912             <policy user="_example">
913               <allow own="com.example.Example1"/>
914             </policy>
915
916             <policy context="default">
917               <allow send_destination="com.example.Example1"/>
918             </policy>
919           </busconfig>
920
921       where _example is the username of the system uid that will run the
922       system service daemon process, and com.example.Example1 is its
923       well-known bus name.
924
925       The policy file for com.example.Example1 should normally be named
926       com.example.Example1.conf.
927
928       Some existing system services rely on more complex <policy> rules to
929       control the messages that the service can receive. However, the
930       dbus-daemon's policy language is not well-suited to finer-grained
931       policies: any policy has to be expressed in terms of D-Bus interfaces
932       and method names, not in terms of higher-level domain-specific concepts
933       like removable or built-in devices. It is recommended that new services
934       should normally accept method call messages from all callers, then
935       apply a sysadmin-controllable policy to decide whether to obey the
936       requests contained in those method call messages, for example by
937       consulting polkit[3].
938
939       Like session services, many D-Bus system services support service
940       activation, a mechanism in which the dbus-daemon can launch the service
941       on-demand, either by running the system service itself or by
942       communicating with systemd. This is set up by creating a service file
943       in the directory ${datadir}/dbus-1/system-services, for example:
944
945           [D-BUS Service]
946           Name=com.example.Example1
947           Exec=/usr/sbin/example-service
948           User=_example
949           # Optional
950           SystemdService=dbus-com.example.Example1.service
951
952       See the D-Bus Specification[2] for details of the contents and
953       interpretation of service files.
954
955       If there is a service file for com.example.Example1, it must be named
956       com.example.Example1.service.
957
958       System services that declare the optional SystemdService must also
959       provide a systemd service unit file whose name or Alias matches the
960       SystemdService (see systemd.unit(5), systemd.service(5) for further
961       details on systemd service units), for example:
962
963           [Unit]
964           Description=Example service
965
966           [Service]
967           Type=dbus
968           BusName=com.example.Example1
969           ExecStart=/usr/sbin/example-service
970
971           [Install]
972           WantedBy=multi-user.target
973           Alias=dbus-com.example.Example1.service
974
975

SELINUX

977       See http://www.nsa.gov/selinux/ for full details on SELinux. Some
978       useful excerpts:
979
980       Every subject (process) and object (e.g. file, socket, IPC object, etc)
981       in the system is assigned a collection of security attributes, known as
982       a security context. A security context contains all of the security
983       attributes associated with a particular subject or object that are
984       relevant to the security policy.
985
986       In order to better encapsulate security contexts and to provide greater
987       efficiency, the policy enforcement code of SELinux typically handles
988       security identifiers (SIDs) rather than security contexts. A SID is an
989       integer that is mapped by the security server to a security context at
990       runtime.
991
992       When a security decision is required, the policy enforcement code
993       passes a pair of SIDs (typically the SID of a subject and the SID of an
994       object, but sometimes a pair of subject SIDs or a pair of object SIDs),
995       and an object security class to the security server. The object
996       security class indicates the kind of object, e.g. a process, a regular
997       file, a directory, a TCP socket, etc.
998
999       Access decisions specify whether or not a permission is granted for a
1000       given pair of SIDs and class. Each object class has a set of associated
1001       permissions defined to control operations on objects with that class.
1002
1003       D-Bus performs SELinux security checks in two places.
1004
1005       First, any time a message is routed from one connection to another
1006       connection, the bus daemon will check permissions with the security
1007       context of the first connection as source, security context of the
1008       second connection as target, object class "dbus" and requested
1009       permission "send_msg".
1010
1011       If a security context is not available for a connection (impossible
1012       when using UNIX domain sockets), then the target context used is the
1013       context of the bus daemon itself. There is currently no way to change
1014       this default, because we're assuming that only UNIX domain sockets will
1015       be used to connect to the systemwide bus. If this changes, we'll
1016       probably add a way to set the default connection context.
1017
1018       Second, any time a connection asks to own a name, the bus daemon will
1019       check permissions with the security context of the connection as
1020       source, the security context specified for the name in the config file
1021       as target, object class "dbus" and requested permission "acquire_svc".
1022
1023       The security context for a bus name is specified with the <associate>
1024       element described earlier in this document. If a name has no security
1025       context associated in the configuration file, the security context of
1026       the bus daemon itself will be used.
1027

APPARMOR

1029       The AppArmor confinement context is stored when applications connect to
1030       the bus. The confinement context consists of a label and a confinement
1031       mode. When a security decision is required, the daemon uses the
1032       confinement context to query the AppArmor policy to determine if the
1033       action should be allowed or denied and if the action should be audited.
1034
1035       The daemon performs AppArmor security checks in three places.
1036
1037       First, any time a message is routed from one connection to another
1038       connection, the bus daemon will check permissions with the label of the
1039       first connection as source, label and/or connection name of the second
1040       connection as target, along with the bus name, the path name, the
1041       interface name, and the member name. Reply messages, such as
1042       method_return and error messages, are implicitly allowed if they are in
1043       response to a message that has already been allowed.
1044
1045       Second, any time a connection asks to own a name, the bus daemon will
1046       check permissions with the label of the connection as source, the
1047       requested name as target, along with the bus name.
1048
1049       Third, any time a connection attempts to eavesdrop, the bus daemon will
1050       check permissions with the label of the connection as the source, along
1051       with the bus name.
1052
1053       AppArmor rules for bus mediation are not stored in the bus
1054       configuration files. They are stored in the application's AppArmor
1055       profile. Please see apparmor.d(5) for more details.
1056

DEBUGGING

1058       If you're trying to figure out where your messages are going or why you
1059       aren't getting messages, there are several things you can try.
1060
1061       Remember that the system bus is heavily locked down and if you haven't
1062       installed a security policy file to allow your message through, it
1063       won't work. For the session bus, this is not a concern.
1064
1065       The simplest way to figure out what's happening on the bus is to run
1066       the dbus-monitor program, which comes with the D-Bus package. You can
1067       also send test messages with dbus-send. These programs have their own
1068       man pages.
1069
1070       If you want to know what the daemon itself is doing, you might consider
1071       running a separate copy of the daemon to test against. This will allow
1072       you to put the daemon under a debugger, or run it with verbose output,
1073       without messing up your real session and system daemons.
1074
1075       To run a separate test copy of the daemon, for example you might open a
1076       terminal and type:
1077
1078             DBUS_VERBOSE=1 dbus-daemon --session --print-address
1079
1080       The test daemon address will be printed when the daemon starts. You
1081       will need to copy-and-paste this address and use it as the value of the
1082       DBUS_SESSION_BUS_ADDRESS environment variable when you launch the
1083       applications you want to test. This will cause those applications to
1084       connect to your test bus instead of the DBUS_SESSION_BUS_ADDRESS of
1085       your real session bus.
1086
1087       DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus was
1088       compiled with verbose mode enabled. This is not recommended in
1089       production builds due to performance impact. You may need to rebuild
1090       D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
1091       also affects the D-Bus library and thus applications using D-Bus; it
1092       may be useful to see verbose output on both the client side and from
1093       the daemon.)
1094
1095       If you want to get fancy, you can create a custom bus configuration for
1096       your test bus (see the session.conf and system.conf files that define
1097       the two default configurations for example). This would allow you to
1098       specify a different directory for .service files, for example.
1099

AUTHOR

1101       See http://www.freedesktop.org/software/dbus/doc/AUTHORS
1102

BUGS

1104       Please send bug reports to the D-Bus mailing list or bug tracker, see
1105       http://www.freedesktop.org/software/dbus/
1106

NOTES

1108        1. relay connections via Secure Shell or a similar protocol
1109           https://lists.freedesktop.org/archives/dbus/2018-April/017447.html
1110
1111        2. D-Bus Specification
1112           https://dbus.freedesktop.org/doc/dbus-specification.html
1113
1114        3. polkit
1115           https://www.freedesktop.org/wiki/Software/polkit/
1116
1117
1118
1119D-Bus 1.14.0                      03/10/2022                    DBUS-DAEMON(1)
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