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


       dbus-daemon - Message bus daemon


       dbus-daemon  dbus-daemon  [--version]  [--session]  [--system]  [--con-
       fig-file=FILE]  [--print-address[=DESCRIPTOR]]   [--print-pid[=DESCRIP-
       TOR]] [--fork]


       dbus-daemon  is  the D-Bus message bus daemon. See http://www.freedesk- for more  information  about  the  big  picture.
       D-Bus is first a library that provides one-to-one communication between
       any two applications; dbus-daemon is  an  application  that  uses  this
       library to implement a message bus daemon. Multiple programs connect to
       the message bus daemon and can exchange messages with one another.

       There are two standard message bus instances:  the  systemwide  message
       bus  (installed  on  many systems as the "messagebus" init service) and
       the per-user-login-session message bus (started each time a  user  logs
       in).   dbus-daemon is used for both of these instances, but with a dif-
       ferent configuration file.

       The     --session     option     is     equivalent      to      "--con-
       fig-file=/usr/local/etc/dbus-1/session.conf" and the --system option is
       equivalent  to  "--config-file=/usr/local/etc/dbus-1/system.conf".   By
       creating  additional  configuration  files  and using the --config-file
       option, additional special-purpose message bus daemons  could  be  cre-

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

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

       The  per-session  daemon is used for various interprocess communication
       among desktop applications (however, it is not tied to X or the GUI  in
       any way).

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


       The following options are supported:

              Use the given configuration file.

       --fork Force  the  message bus to fork and become a daemon, even if the
              configuration file does not specify that  it  should.   In  most
              contexts the configuration file already gets this right, though.
              --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

              Print the version of the daemon.

              Print  the  introspection  information  for  all  D-Bus internal

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

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

              Don't write a PID file even if one is configured in the configu-
              ration 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 forth.

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

       The  standard systemwide and per-session message bus setups are config-
       ured   in    the    files    "/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 namespaced.  The last <type>  ele-
       ment  "wins"  (previous values are ignored). This element only controls
       which message bus specific environment variables are set  in  activated
       clients.   Most of the policy that distinguishes a session bus from the
       system bus is controlled from the other elements in  the  configuration

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

       Example: <type>session</type>


       Include a file <include>filename.conf</include> at this point.  If  the
       filename  is relative, it is located relative to the configuration file
       doing the including.

       <include> has an  optional  attribute  "ignore_missing=(yes|no)"  which
       defaults  to "no" if not provided. This attribute controls whether it's
       a fatal error for the included file to be absent.


       Include all files  in  <includedir>foo.d</includedir>  at  this  point.
       Files  in  the  directory  are included in undefined order.  Only files
       ending in ".conf" are included.

       This is intended to allow extension of the  system  bus  by  particular
       packages.  For  example, if CUPS wants to be able to send out notifica-
       tion  of  printer  queue  changes,  it  could   install   a   file   to
       /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


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


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


       Add an address that the bus should listen on. The  address  is  in  the
       standard  D-Bus  format  that  contains  a transport name plus possible

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

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

       If there are multiple <listen> elements, then the bus listens on multi-
       ple  addresses.  The  bus  will pass its address to started services or
       other interested parties with the last address given in <listen> first.
       That is, apps will try to connect to the last <listen> address first.

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

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

       A special case is using a port number of zero (or omitting  the  port),
       which  means to choose an available port selected by the operating sys-
       tem. The port number chosen can be obtained  with  the  --print-address
       command  line  parameter  and  will be present in other cases where the
       server reports its own address, such as  when  DBUS_SESSION_BUS_ADDRESS
       is set.

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

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

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


       Lists permitted  authorization  mechanisms.  If  this  element  doesn't
       exist,  then  all  known mechanisms are allowed.  If there are multiple
       <auth> elements, all the listed mechanisms are allowed.  The  order  in
       which mechanisms are listed is not meaningful.

       Example: <auth>EXTERNAL</auth>

       Example: <auth>DBUS_COOKIE_SHA1</auth>


       Adds  a  directory  to scan for .service files. Directories are scanned
       starting with the last to appear in the config file (the first .service
       file found that provides a particular service will be used).

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


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

       The "XDG Base Directory Specification" can be found at http://freedesk- 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/ses-
       sion.conf. Putting it in any other configuration file would probably be


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

       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 dae-
       mon defined in /usr/local/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_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_completed_connections  divided  by  max_connections_per_user is the
       number of users that can work together to denial-of-service  all  other
       users by using up all connections on the systemwide bus.

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


       The <policy> element defines a security policy to be applied to a  par-
       ticular  set  of connections to the bus. A policy is made up of <allow>
       and <deny> elements. Policies are normally  used  with  the  systemwide
       bus; they are analogous to a firewall in that they allow expected traf-
       fic and prevent unexpected traffic.

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

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

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

       Policies are applied to a connection as follows:
          - all context="default" policies are applied
          - all group="connection's user's group" policies are applied
            in undefined order
          - all user="connection's auth user" policies are applied
            in undefined order
          - all at_console="true" policies are applied
          - all at_console="false" policies are applied
          - all context="mandatory" policies are applied

       Policies applied later will override those applied  earlier,  when  the
       policies  overlap.  Multiple  policies with the same user/group/context
       are applied in the order they appear in the config file.

       <deny> <allow>

       A <deny> element appears below a <policy> element  and  prohibits  some
       action.  The  <allow>  element  makes  an  exception to previous <deny>
       statements, and works just like <deny> but with the inverse meaning.

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

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

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

          eavesdrop="true" | "false"


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

       The <deny> element's attributes determine whether the deny "matches"  a
       particular  action.  If  it matches, the action is denied (unless later
       rules in the config file allow it).

       send_destination and receive_sender rules mean that messages may not be
       sent  to  or received from the *owner* of the given name, not that they
       may not be sent *to that name*. That is, if a connection owns  services
       A,  B,  C,  and sending to A is denied, sending to B or C will not work

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

       "Eavesdropping"  occurs when an application receives a message that was
       explicitly addressed to a name the application does not own,  or  is  a
       reply  to  such  a message. Eavesdropping thus only applies to messages
       that are addressed to services and replies to such  messages  (i.e.  it
       does not apply to signals).

       For <allow>, eavesdrop="true" indicates that the rule matches even when
       eavesdropping. eavesdrop="false" is the default and means that the rule
       only  allows  messages to go to their specified recipient.  For <deny>,
       eavesdrop="true" indicates that the rule matches only  when  eavesdrop-
       ping.  eavesdrop="false"  is  the  default for <deny> also, but here it
       means that the rule applies always, even when  not  eavesdropping.  The
       eavesdrop  attribute  can  only be combined with send and receive rules
       (with send_* and receive_* attributes).

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

       For <allow>, [send|receive]_requested_reply="true" is the  default  and
       indicates  that  only  requested  replies  are  allowed  by  the  rule.
       [send|receive]_requested_reply="false" means that the rule  allows  any
       reply even if unexpected.

       For  <deny>,  [send|receive]_requested_reply="false" is the default but
       indicates that the rule matches only when the reply was not  requested.
       [send|receive]_requested_reply="true"  indicates  that the rule applies
       always, regardless of pending reply state.

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

       For  "name",  "username",  "groupname",  etc.  the character "*" can be
       substituted, meaning  "any."  Complex  globs  like  "*"  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.ConnectionMan-
       ager.(anything) and org.freedesktop.ReserveDevice1.(anything).

       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_inter-
       face="" 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.freedesk-
       top.Foobar" then the source context will be the context of the  connec-
       tion  and the target context will be "foo_t" - see the short discussion
       of SELinux below.

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

       There's  currently  no  way to set a default for owning any name, if we
       add this syntax it will look like:
          <associate own="*" context="foo_t"/>
       If you find a reason this is useful, let the  developers  know.   Right
       now the default will be the security context of the bus itself.

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


       See for full details on SELinux. Some  use-
       ful excerpts:

               Every  subject  (process)  and  object  (e.g. file, socket, IPC
               object, etc) in the system is assigned a collection of security
               attributes,  known  as  a  security context. A security context
               contains all of the security attributes associated with a  par-
               ticular  subject  or  object  that are relevant to the security

               In order to better encapsulate security contexts and to provide
               greater efficiency, the policy enforcement code of SELinux typ-
               ically handles security identifiers (SIDs) rather than security
               contexts.  A  SID  is an integer that is mapped by the security
               server to a security context at runtime.

               When a security decision is required,  the  policy  enforcement
               code  passes a pair of SIDs (typically the SID of a subject and
               the SID of an object, but sometimes a pair of subject SIDs or a
               pair of object SIDs), and an object security class to the secu-
               rity server. The object security class indicates  the  kind  of
               object,  e.g.  a  process,  a  regular file, a directory, a TCP
               socket, etc.

               Access decisions specify whether or not a permission is granted
               for a given pair of SIDs and class. Each object class has a set
               of associated permissions  defined  to  control  operations  on
               objects with that class.

       D-Bus performs SELinux security checks in two places.

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

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

       Second, any time a connection asks to own a name, the bus  daemon  will
       check  permissions  with  the  security  context  of  the connection as
       source, the security context specified for the name in the config  file
       as  target, object class "dbus" and requested permission "acquire_svc".

       The security context for a bus name is specified with  the  <associate>
       element  described earlier in this document.  If a name has no security
       context associated in the configuration file, the security  context  of
       the bus daemon itself will be used.


       If you're trying to figure out where your messages are going or why you
       aren't getting messages, there are several things you can try.

       Remember that the system bus is heavily locked down and if you  haven't
       installed  a  security  policy  file  to allow your message through, it
       won't work. For the session bus, this is not a concern.

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

       If you want to know what the daemon itself is doing, you might consider
       running a separate copy of the daemon to test against. This will  allow
       you  to put the daemon under a debugger, or run it with verbose output,
       without messing up your real session and system daemons.

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

       The  test  daemon  address  will be printed when the daemon starts. You
       will need to copy-and-paste this address and use it as the value of the
       DBUS_SESSION_BUS_ADDRESS  environment  variable  when  you  launch  the
       applications you want to test. This will cause  those  applications  to
       connect  to  your  test  bus instead of the DBUS_SESSION_BUS_ADDRESS of
       your real session bus.

       DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus  was  com-
       piled  with verbose mode enabled. This is not recommended in production
       builds due to performance impact. You may need to rebuild D-Bus if your
       copy  was  not built with debugging in mind. (DBUS_VERBOSE also affects
       the D-Bus library and thus applications using D-Bus; it may  be  useful
       to see verbose output on both the client side and from the daemon.)

       If you want to get fancy, you can create a custom bus configuration for
       your test bus (see the session.conf and system.conf files  that  define
       the  two  default  configurations for example). This would allow you to
       specify a different directory for .service files, for example.




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

dbus 1.6.0 - Generated Thu Jun 7 15:01:12 CDT 2012
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