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X11R7.4 - man page for dbus-daemon (x11r4 section 1)

dbus-daemon(1)			     General Commands Manual			   dbus-daemon(1)

       dbus-daemon - Message bus daemon

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

       dbus-daemon is the D-Bus message bus daemon. See http://www.freedesktop.org/software/dbus/
       for more information about the big picture. D-Bus is first a library that provides one-to-
       one communication between any two applications; 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 different configuration file.

       The  --session  option is equivalent to "--config-file=/usr/local/etc/dbus-1/session.conf"
       and  the  --system  option  is  equivalent  to	"--config-file=/usr/local/etc/dbus-1/sys-
       tem.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,  standardly  called  simply

       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 appli-
       cations (however, it is not tied to X or the GUI in any way).

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

       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 bus.

	      Print the version of the daemon.

       A message bus daemon has a configuration file that specializes it for a particular  appli-
       cation.	For  example,  one  configuration  file might set up the message bus to be a sys-
       temwide 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

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

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

       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 names-
       paced.	The  last  <type> element "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 file.

       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 mes-
       sage  bus  is "system", then the DBUS_STARTER_BUS_TYPE environment variable will be set to
       "system" and the DBUS_SESSION_BUS_ADDRESS environment variable 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 rela-
       tive, 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 notification  of  printer  queue  changes,	it  could
       install	a  file  to  /usr/local/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 writing.


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


       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 parameters/options.

       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 multiple  addresses.  The
       bus  will  pass	its address to started services or other interested parties with the last
       address given in <listen> first. That is, apps will try to connect to  the  last  <listen>
       address first.

       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 system. 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

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

       tcp addresses also allow a bind=hostname option, which will override the host option spec-
       ifying what address to bind to, without changing the address reported by the bus. The bind
       option  can  also  take a special 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  particu-
       lar 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 bus.


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

       The  "XDG  Base Directory Specification" can be found at http://freedesktop.org/wiki/Stan-
       dards/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 /usr/local/etc/dbus-1/session.conf. Putting it in any other configura-
       tion file would probably be nonsense.


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

       The <standard_system_servicedirs/> option is only relevant to the  per-system  bus  daemon
       defined	in  /usr/local/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  daemon  defined  in
       /usr/local/etc/dbus-1/system.conf. Putting it in any other configuration file would proba-
       bly 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_message_size.

       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 particular set of con-
       nections to the bus. A policy is made up of <allow> and <deny> elements. Policies are nor-
       mally  used  with  the systemwide bus; they are analogous to a firewall in that they allow
       expected traffic 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 messages, receive checks, and signals has
       a default allow policy.

       In general, it is best to keep system services as small, targeted programs  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_destina-
       tion" rule to allow traffic from some or all uids to your service.

       The <policy> element has one of four attributes: daemon.1.in
	 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_interface="org.freedesktop.System" send_member="Reboot"/>
	  <deny receive_interface="org.freedesktop.System" receive_member="Reboot"/>
	  <deny own="org.freedesktop.System"/>
	  <deny send_destination="org.freedesktop.System"/>
	  <deny receive_sender="org.freedesktop.System"/>
	  <deny user="john"/>
	  <deny group="enemies"/>

       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 either.

       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. Eaves-
       dropping 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 eavesdropping. eavesdrop="false" is the default for <deny>  also,  but  here  it
       means  that  the rule applies always, even when not eavesdropping. The eavesdrop attribute
       can only be combined with send and receive rules (with send_* and receive_* attributes).

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

       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 connect to the message

       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_destina-
       tion="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_interface="org.foo.Bar"


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


       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.freedesktop.Foobar"	then  the
       source  context	will  be  the  context	of  the connection and the target context will be
       "foo_t" - see the short discussion of SELinux below.

       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 appearing later in the con-
       figuration file will be used.

       See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful 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 con-
	       text. A security context contains all of the security attributes associated with a
	       particular subject or object that are relevant to the security policy.

	       In  order  to  better  encapsulate  security contexts and to provide greater effi-
	       ciency, the policy enforcement code of SELinux typically handles security  identi-
	       fiers  (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  security 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  connection,  the  bus
       daemon will check permissions with the security context of the first connection as source,
       security context of the second connection as target, object  class  "dbus"  and	requested
       permission "send_msg".

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

       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

       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 configura-
       tion 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 secu-
       rity 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 pro-
       gram, 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  debug-
       ger,  or  run it with verbose output, without messing up your real session and system dae-

       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 applica-
       tions  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  compiled  with  verbose
       mode  enabled. This is not recommended in production builds due to performance impact. You
       may need to rebuild D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE
       also  affects the D-Bus library and thus applications using D-Bus; it may be useful to see
       verbose output on both the client side and from the daemon.)

       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

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

       Please send bug reports to the D-Bus mailing list or bug tracker, see http://www.freedesk-


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