Provided by: dbus_1.4.18-1ubuntu1_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.

              Enable  upstart-style  service  activation.  Only  useful  in  conjunction with the
              Upstart init daemon on Linux.


       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.

       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.


       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.


       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