Provided by: dbus_1.6.18-0ubuntu4_amd64 bug


       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
       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

       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.  --nofork Force the message bus not to fork and  become  a
              daemon, even if the configuration file specifies that it should.

              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.

              Print the introspection information for all D-Bus internal interfaces.

              Set  the  address to listen on. This option overrides the address configured in the
              configuration file.

              Enable systemd-style service  activation.  Only  useful  in  conjunction  with  the
              systemd system and session manager on Linux.

              Don't write a PID file even if one is configured in the configuration files.


       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

       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 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
       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 bus.


       <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

       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


       <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_incoming_unix_fds"      : total number of unix fds of messages
                                            incoming from a single connection
             "max_outgoing_bytes"         : total size in bytes of messages
                                            queued up for a single connection
             "max_outgoing_unix_fds"      : total number of unix fds of messages
                                            queued up for a single connection
             "max_message_size"           : max size of a single message in
             "max_message_unix_fds"       : max unix fds of a single message
             "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
       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_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 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.
       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

       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.

       <allow own_prefix="a.b"/> allows you to own the name "a.b" or any name  whose  first  dot-
       separated  elements  are  "a.b":  in particular, you can own "a.b.c" or "a.b.c.d", but not
       "a.bc" or "a.c".  This is useful when services like Telepathy and ReserveDevice  define  a
       meaning       for       subtrees       of       well-known       names,       such      as
       org.freedesktop.Telepathy.ConnectionManager.(anything)                                 and

       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=""


       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
       configuration file will be used.


       The  <apparmor>  element is used to configure AppArmor mediation of D-Bus messages. It can
       contain one attibute that specifies if mediation is enabled:
         <apparmor mode="(enabled|disabled|required)"/>
       The default mode is is "enabled". In "enabled" mode, AppArmor mediation will be enabled if
       AppArmor  support  is  available.  In  "disabled" mode, AppArmor mediation is disabled. In
       "required" mode, AppArmor mediation will be enabled  if  AppArmor  support  is  available,
       otherwise D-Bus will not start.


       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 policy.

               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

       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.


       The  AppArmor  confinement  context  is  stored  when  applications connect to D-Bus.  The
       confinement context consists of a label and a confinement mode. When a  security  decision
       is  required, D-Bus uses the label to query the AppArmor policy to determine if the action
       should be allowed, denied, and/or audited.

       D-Bus performs AppArmor 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 label of the first connection as source, label
       and/or connection name of the second connection as target, along with the  bus  name,  the
       path  name, the interface name, and the member name. Reply messages, such as method_return
       and error messages, are implicity allowed if they are in response to a  message  that  has
       already been allowed.

       Second,  any  time  a connection asks to own a name, the bus daemon will check permissions
       with the label of the connection as source, the requested name as target, along  with  the
       bus name.

       AppArmor rules for D-Bus mediation are not stored in the bus configuration files. They are
       stored in the application's AppArmor profile. Please see the  AppArmor  documentation  for
       more details.


       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

       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




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