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       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 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=/etc/dbus-1/session.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,
       standardly 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
       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

              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
       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    "/etc/dbus-1/system.conf"    and
       "/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  namespaced.  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 message 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 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
       notification  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
       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

       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

       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 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
       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 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
       directories searched.

       The    "XDG   Base   Directory   Specification"   can   be   found   at 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
       activation 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
       daemon defined in /etc/dbus-1/system.conf.  Putting  it  in  any  other
       configuration 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
       particular  set  of  connections  to  the  bus.  A policy is made up of
       <allow> and <deny>  elements.  Policies  are  normally  used  with  the
       systemwide  bus;  they  are  analogous to a firewall in that they allow
       expected traffic and prevent unexpected traffic.

       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_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_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

       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
       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 bus.

       For  "name",  "username",  "groupname",  etc.  the character "*" can be
       substituted, meaning  "any."  Complex  globs  like  "*"  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="" 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=""/>!   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="" send_destination=""/>


       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.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 configuration file will be used.


       See  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  context.  A  security  context
               contains  all  of  the  security  attributes  associated with a
               particular 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
               typically  handles  security  identifiers  (SIDs)  rather  than
               security contexts. A SID is an integer that is  mapped  by  the
               security server to a security context at runtime.

               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  "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
       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 example.




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