2 .\" dbus-daemon-1 manual page.
3 .\" Copyright (C) 2003 Red Hat, Inc.
7 dbus-daemon-1 \- Message bus daemon
11 dbus-daemon-1 [\-\-version] [\-\-session] [\-\-system] [\-\-config-file=FILE]
12 [\-\-print-address[=DESCRIPTOR]] [\-\-print-pid[=DESCRIPTOR]] [\-\-fork]
16 \fIdbus-daemon-1\fP is the D-BUS message bus daemon. See
17 http://www.freedesktop.org/software/dbus/ for more information about
18 the big picture. D-BUS is first a library that provides one-to-one
19 communication between any two applications; \fIdbus-daemon-1\fP is an
20 application that uses this library to implement a message bus
21 daemon. Multiple programs connect to the message bus daemon and can
22 exchange messages with one another.
25 There are two standard message bus instances: the systemwide message bus
26 (installed on many systems as the "messagebus" service) and the
27 per-user-login-session message bus (started each time a user logs in).
28 \fIdbus-daemon-1\fP is used for both of these instances, but with
29 a different configuration file.
32 The \-\-session option is equivalent to
33 "\-\-config-file=@EXPANDED_SYSCONFDIR@/dbus-1/session.conf" and the \-\-system
34 option is equivalent to
35 "\-\-config-file=@EXPANDED_SYSCONFDIR@/dbus-1/system.conf". By creating
36 additional configuration files and using the \-\-config-file option,
37 additional special-purpose message bus daemons could be created.
40 The systemwide daemon is normally launched by an init script,
41 standardly called simply "messagebus".
44 The systemwide daemon is largely used for broadcasting system events,
45 such as changes to the printer queue, or adding/removing devices.
48 The per-session daemon is used for various interprocess communication
49 among desktop applications (however, it is not tied to X or the GUI
53 There is no way to cause the D-BUS daemon to reload its configuration
54 file (HUP will not do so). The reason is that changing configuration
55 would break the semantics expected by applications connected to the
56 message bus. Thus, changing configuration would require kicking all
57 apps off the bus; so you may as well just restart the daemon.
60 The following options are supported:
62 .I "--config-file=FILE"
63 Use the given configuration file.
66 Force the message bus to fork and become a daemon, even if
67 the configuration file does not specify that it should.
68 In most contexts the configuration file already gets this
71 .I "--print-address[=DESCRIPTOR]"
72 Print the address of the message bus to standard output, or
73 to the given file descriptor. This is used by programs that
74 launch the message bus.
76 .I "--print-pid[=DESCRIPTOR]"
77 Print the process ID of the message bus to standard output, or
78 to the given file descriptor. This is used by programs that
79 launch the message bus.
82 Use the standard configuration file for the per-login-session message
86 Use the standard configuration file for the systemwide message bus.
89 Print the version of the daemon.
91 .SH CONFIGURATION FILE
93 A message bus daemon has a configuration file that specializes it
94 for a particular application. For example, one configuration
95 file might set up the message bus to be a systemwide message bus,
96 while another might set it up to be a per-user-login-session bus.
99 The configuration file also establishes resource limits, security
100 parameters, and so forth.
103 The configuration file is not part of any interoperability
104 specification and its backward compatibility is not guaranteed; this
105 document is documentation, not specification.
108 The standard systemwide and per-session message bus setups are
109 configured in the files "@EXPANDED_SYSCONFDIR@/dbus-1/system.conf" and
110 "@EXPANDED_SYSCONFDIR@/dbus-1/session.conf". These files normally
111 <include> a system-local.conf or session-local.conf; you can put local
112 overrides in those files to avoid modifying the primary configuration
116 The configuration file is an XML document. It must have the following
120 <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
121 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
126 The following elements may be present in the configuration file.
138 The well-known type of the message bus. Currently known values are
139 "system" and "session"; if other values are set, they should be
140 either added to the D-BUS specification, or namespaced. The last
141 <type> element "wins" (previous values are ignored).
144 Example: <type>session</type>
150 Include a file <include>filename.conf</include> at this point. If the
151 filename is relative, it is located relative to the configuration file
155 <include> has an optional attribute "ignore_missing=(yes|no)"
156 which defaults to "no" if not provided. This attribute
157 controls whether it's a fatal error for the included file
164 Include all files in <includedir>foo.d</includedir> at this
165 point. Files in the directory are included in undefined order.
166 Only files ending in ".conf" are included.
169 This is intended to allow extension of the system bus by particular
170 packages. For example, if CUPS wants to be able to send out
171 notification of printer queue changes, it could install a file to
172 @EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
173 this message and allowed the printer daemon user to send it.
179 The user account the daemon should run as, as either a username or a
180 UID. If the daemon cannot change to this UID on startup, it will exit.
181 If this element is not present, the daemon will not change or care
185 The last <user> entry in the file "wins", the others are ignored.
188 The user is changed after the bus has completed initialization. So
189 sockets etc. will be created before changing user, but no data will be
190 read from clients before changing user. This means that sockets
191 and PID files can be created in a location that requires root
192 privileges for writing.
198 If present, the bus daemon becomes a real daemon (forks
199 into the background, etc.). This is generally used
200 rather than the \-\-fork command line option.
206 Add an address that the bus should listen on. The
207 address is in the standard D-BUS format that contains
208 a transport name plus possible parameters/options.
211 Example: <listen>unix:path=/tmp/foo</listen>
214 If there are multiple <listen> elements, then the bus listens
215 on multiple addresses. The bus will pass its address to
216 activated services or other interested parties with
217 the last address given in <listen> first. That is,
218 apps will try to connect to the last <listen> address first.
224 Lists permitted authorization mechanisms. If this element doesn't
225 exist, then all known mechanisms are allowed. If there are multiple
226 <auth> elements, all the listed mechanisms are allowed. The order in
227 which mechanisms are listed is not meaningful.
230 Example: <auth>EXTERNAL</auth>
233 Example: <auth>DBUS_COOKIE_SHA1</auth>
239 Adds a directory to scan for .service files. Directories are
240 scanned starting with the last to appear in the config file
241 (the first .service file found that provides a particular
242 service will be used).
245 Service files tell the bus how to automatically start a particular
246 service. They are primarily used with the per-user-session bus,
247 not the systemwide bus.
253 <limit> establishes a resource limit. For example:
255 <limit name="max_message_size">64</limit>
256 <limit name="max_completed_connections">512</limit>
260 The name attribute is mandatory.
261 Available limit names are:
263 "max_incoming_bytes" : total size in bytes of messages
264 incoming from a single connection
265 "max_outgoing_bytes" : total size in bytes of messages
266 queued up for a single connection
267 "max_message_size" : max size of a single message in
269 "activation_timeout" : milliseconds (thousandths) until
270 an activated service has to connect
271 "auth_timeout" : milliseconds (thousandths) a
272 connection is given to
274 "max_completed_connections" : max number of authenticated connections
275 "max_incomplete_connections" : max number of unauthenticated
277 "max_connections_per_user" : max number of completed connections from
279 "max_pending_activations" : max number of activations in
280 progress at the same time
281 "max_services_per_connection": max number of services a single
286 The max incoming/outgoing queue sizes allow a new message to be queued
287 if one byte remains below the max. So you can in fact exceed the max
291 max_completed_connections divided by max_connections_per_user is the
292 number of users that can work together to DOS all other users by using
299 The <policy> element defines a policy to be applied to a particular
300 set of connections to the bus. A policy is made up of
301 <allow> and <deny> elements.
304 The <policy> element has one of three attributes:
306 context="(default|mandatory)"
307 user="username or userid"
308 group="group name or gid"
313 Policies are applied to a connection as follows:
315 - all context="default" policies are applied
316 - all group="connection's user's group" policies are applied
318 - all user="connection's auth user" policies are applied
320 - all context="mandatory" policies are applied
324 Policies applied later will override those applied earlier,
325 when the policies overlap. Multiple policies with the same
326 user/group/context are applied in the order they appear
333 A <deny> element appears below a <policy> element and prohibits
334 some action. The possible attributes of a <deny> element are:
337 receive="messagename"
339 send_to="servicename"
340 receive_from="servicename"
348 <deny send="org.freedesktop.System.Reboot"/>
349 <deny receive="org.freedesktop.System.Reboot"/>
350 <deny own="org.freedesktop.System"/>
351 <deny send_to="org.freedesktop.System"/>
352 <deny receive_from="org.freedesktop.System"/>
354 <deny group="enemies"/>
358 The <deny> attributes determine whether the deny "matches" a
359 particular action. If it matches, the action is denied (unless later
360 rules in the config file allow it).
363 send_to and receive_from mean that messages may not be sent to or
364 received from the *owner* of the given service, not that they may not
365 be sent *to that service name*. That is, if a connection owns services
366 A, B, C, and sending to A is denied, sending to B or C will not work
370 user and group denials mean that the given user or group may
371 not connect to the message bus.
374 For "servicename" or "messagename" or "username" or "groupname"
375 the character "*" can be substituted, meaning "any." Complex globs
376 like "foo.bar.*" aren't allowed for now because they'd be work to
377 implement and maybe encourage sloppy security anyway.
380 It does not make sense to deny a user or group inside a <policy>
381 for a user or group; user/group denials can only be inside
382 context="default" or context="mandatory" policies.
385 A single <deny> rule may specify both send and send_to, OR both
386 receive and receive_from. In this case, the denial applies only if
387 both attributes match the message being denied.
388 e.g. <deny send="foo.bar" send_to="foo.blah"/> would deny
389 messages of the given name AND to the given service.
395 Makes an exception to previous <deny> statements. Works
396 just like <deny> but with the inverse meaning.
399 See http://www.freedesktop.org/software/dbus/doc/AUTHORS
402 Please send bug reports to the D-BUS mailing list or bug tracker,
403 see http://www.freedesktop.org/software/dbus/