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

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

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

       The --session option is equivalent  to  "--config-file=/etc/dbus-1/ses-
       sion.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,  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.

              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 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  "/etc/dbus-1/system.conf"  and  "/etc/dbus-1/ses-
       sion.conf".  These files normally <include> a system-local.conf or ses-
       sion-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
       /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-
       top.org/wiki/Standards/basedir-spec if it hasn't moved,  otherwise  try
       your favorite search engine.

       The <standard_session_servicedirs/> option is only relevant to the per-
       user-session bus daemon defined in /etc/dbus-1/session.conf. Putting it
       in any other configuration file would probably be nonsense.


       <standard_system_servicedirs/> specifies the standard system-wide acti-
       vation 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 dae-
       mon defined in /etc/dbus-1/system.conf. Putting it in any other config-
       uration 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  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
       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 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: daemon.1.in
         user="username or userid"
         group="group name or gid"

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

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

       <deny> <allow>

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

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

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

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

          eavesdrop="true" | "false"


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

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

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

       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  "foo.bar.*"  aren't
       allowed for now because they'd be work to implement and maybe encourage
       sloppy security anyway.

       It does not make sense to deny a user or group inside a <policy> for  a
       user  or group; user/group denials can only be inside context="default"
       or context="mandatory" policies.

       A single <deny> rule may specify combinations  of  attributes  such  as
       send_destination  and  send_interface  and send_type. In this case, the
       denial applies only if both attributes match the message being  denied.
       e.g. <deny send_interface="foo.bar" send_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="org.foo.Bar"/>!   This will cause no-interface messages
       to be blocked for all services, which is almost certainly not what  you
       intended.    Always   use   rules   of   the  form:  <deny  send_inter-
       face="org.foo.Bar" send_destination="org.foo.Service"/>


       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  http://www.nsa.gov/selinux/ 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.

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

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


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