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dbus-daemon(1)							dbus-daemon(1)

       dbus-daemon - Message bus daemon

       dbus-daemon  dbus-daemon	 [--version] [--session] [--system] [--config-
       file=FILE]  [--print-address[=DESCRIPTOR]]   [--print-pid[=DESCRIPTOR]]

       dbus-daemon  is	the D-Bus message bus daemon. See http://www.freedesk‐
       top.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; dbus-daemon 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.

       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).   dbus-daemon is used for both of these instances, but with a dif‐
       ferent configuration file.

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

       The systemwide daemon is normally launched by  an  init	script,	 stan‐
       dardly called simply "messagebus".

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

       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).

       SIGHUP will cause the D-Bus daemon to PARTIALLY reload  its  configura‐
       tion file and to flush its user/group information caches. Some configu‐
       ration 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.

       The following options are supported:

	      Use the given configuration file.

       --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.

	      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.

	      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.

	      Use the standard configuration file  for	the  per-login-session
	      message bus.

	      Use  the	standard configuration file for the systemwide message

	      Print the version of the daemon.

       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.

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

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

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

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

	  <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"

       The following elements may be present in the configuration file.


       Root element.


       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> ele‐
       ment "wins" (previous values are ignored). This element	only  controls
       which  message  bus specific environment variables are set in activated
       clients.	 Most of the policy that distinguishes a session bus from  the
       system  bus  is controlled from the other elements in the configuration

       If the well-known type of  the  message	bus  is	 "session",  then  the
       DBUS_STARTER_BUS_TYPE environment variable will be set to "session" and
       the DBUS_SESSION_BUS_ADDRESS environment variable will be  set  to  the
       address	of  the session bus.  Likewise, if the type of the message bus
       is "system", then the DBUS_STARTER_BUS_TYPE environment	variable  will
       be  set	to "system" and the DBUS_SESSION_BUS_ADDRESS environment vari‐
       able will be set to the address of the system bus  (which  is  normally
       well known anyway).

       Example: <type>session</type>


       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.

       <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.


       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.

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


       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.

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

       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


       If present, the bus daemon becomes a real daemon (forks into the	 back‐
       ground,	etc.).	This  is generally used rather than the --fork command
       line option.


       If present, the bus daemon keeps its original umask when forking.  This
       may be useful to avoid affecting the behavior of child processes.


       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

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

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

       If there are multiple <listen> elements, then the bus listens on multi‐
       ple 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.

       tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames.  If
       a  hostname resolves to multiple addresses, the server will bind to all
       of them. The family=ipv4 or family=ipv6 options can be used to force it
       to bind to a subset of addresses

       Example: <listen>tcp:host=localhost,port=0,family=ipv4</listen>

       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  sys‐
       tem.  The  port	number chosen can be obtained 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.

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

       tcp addresses also allow a bind=hostname option,	 which	will  override
       the  host  option  specifying what address to bind to, without changing
       the address reported by the bus. The bind option can also take  a  spe‐
       cial  name  '*'	to  cause  the	bus  to	 listen	 on  all local address
       (INADDR_ANY). The specified host should be a valid name	of  the	 local
       machine or weird stuff will happen.

       Example: <listen>tcp:host=localhost,bind=*,port=0</listen>


       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.

       Example: <auth>EXTERNAL</auth>

       Example: <auth>DBUS_COOKIE_SHA1</auth>


       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).

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


       <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 directo‐
       ries searched.

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

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


       <standard_system_servicedirs/> specifies the standard system-wide acti‐
       vation  directories  that  should  be searched for service files.  This
       option defaults to /usr/share/dbus-1/system-services.

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


       <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.

       The <servicehelper/> option is only relevant to the per-system bus dae‐
       mon defined in /etc/dbus-1/system.conf. Putting it in any other config‐
       uration file would probably be nonsense.


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

       The name attribute is mandatory.	 Available limit names are:
	     "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
	     "service_start_timeout"	  : milliseconds (thousandths) until
					    a started service has to connect
	     "auth_timeout"		  : milliseconds (thousandths) a
					    connection is given to
	     "max_completed_connections"  : max number of authenticated connections
	     "max_incomplete_connections" : max number of unauthenticated
	     "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
	     "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

       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_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.

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


       The  <policy> element defines a security policy to be applied to a par‐
       ticular 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 traf‐
       fic and prevent unexpected traffic.

       Currently,  the system bus has a default-deny policy for sending method
       calls and owning bus names.  Everything else, in particular reply  mes‐
       sages, receive checks, and signals has a default allow policy.

       In  general, it is best to keep system services as small, targeted pro‐
       grams which run in their own process and provide	 a  single  bus	 name.
       Then, all that is needed is an <allow> rule for the "own" permission to
       let the process claim the bus name, and a  "send_destination"  rule  to
       allow traffic from some or all uids to your service.

       The <policy> element has one of four attributes:
	 user="username or userid"
	 group="group name or gid"

       Policies are applied to a connection as follows:
	  - 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 at_console="true" policies are applied
	  - all at_console="false" policies are applied
	  - all context="mandatory" policies are applied

       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.

       <deny> <allow>

       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.

       The possible attributes of these elements are:
	  send_type="method_call" | "method_return" | "signal" | "error"

	  receive_type="method_call" | "method_return" | "signal" | "error"

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

	  eavesdrop="true" | "false"


	  <deny send_destination="org.freedesktop.Service" send_interface="org.freedesktop.System" send_member="Reboot"/>
	  <deny send_destination="org.freedesktop.System"/>
	  <deny receive_sender="org.freedesktop.System"/>
	  <deny user="john"/>
	  <deny group="enemies"/>

       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).

       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

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

       "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).

       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 eavesdrop‐
       ping. 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).

       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 mes‐
       sage).  This attribute only makes sense for reply messages (errors  and
       method returns), and is ignored for other message types.

       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.

       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.

       user  and  group denials mean that the given user or group may not con‐
       nect to the message bus.

       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.

       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.

       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.

       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.

       Be careful with send_interface/receive_interface, because the interface
       field  in  messages  is	optional.  In particular, do NOT specify <deny
       send_interface="org.foo.Bar"/>!	This will cause no-interface  messages
       to  be blocked for all services, which is almost certainly not what you
       intended.   Always  use	rules	of   the   form:   <deny   send_inter‐
       face="org.foo.Bar" send_destination="org.foo.Service"/>


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


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

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

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

       There's	currently  no  way to set a default for owning any name, if we
       add this syntax it will look like:
	  <associate own="*" context="foo_t"/>
       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.

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

       See http://www.nsa.gov/selinux/ for full details on SELinux. Some  use‐
       ful excerpts:

	       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  par‐
	       ticular	subject	 or  object  that are relevant to the security

	       In order to better encapsulate security contexts and to provide
	       greater efficiency, the policy enforcement code of SELinux typ‐
	       ically 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.

	       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 secu‐
	       rity server. The object security class indicates	 the  kind  of
	       object,	e.g.  a	 process,  a  regular file, a directory, a TCP
	       socket, etc.

	       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.

       D-Bus performs SELinux security checks in two places.

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

       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 proba‐
       bly add a way to set the default connection context.

       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".

       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.

       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.

       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.

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

       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.

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

       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.

       DBUS_VERBOSE=1  will  have NO EFFECT unless your copy of D-Bus was com‐
       piled 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.)

       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.

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

       Please  send  bug reports to the D-Bus mailing list or bug tracker, see


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