path: root/bus/dbus-daemon-1.1.in

.\" 
.\" dbus-daemon-1 manual page.
.\" Copyright (C) 2003 Red Hat, Inc.
.\"
.TH dbus-daemon-1 1
.SH NAME
dbus-daemon-1 \- Message bus daemon
.SH SYNOPSIS
.PP
.B dbus-daemon-1
dbus-daemon-1 [\-\-version] [\-\-session] [\-\-system] [\-\-config-file=FILE]
[\-\-print-address[=DESCRIPTOR]] [\-\-print-pid[=DESCRIPTOR]] [\-\-fork]

.SH DESCRIPTION

\fIdbus-daemon-1\fP is the D-BUS message bus daemon. See
http://www.freedesktop.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; \fIdbus-daemon-1\fP 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.

.PP
There are two standard message bus instances: the systemwide message bus 
(installed on many systems as the "messagebus" service) and the 
per-user-login-session message bus (started each time a user logs in).
\fIdbus-daemon-1\fP is used for both of these instances, but with 
a different configuration file.

.PP
The \-\-session option is equivalent to
"\-\-config-file=@EXPANDED_SYSCONFDIR@/dbus-1/session.conf" and the \-\-system
option is equivalent to
"\-\-config-file=@EXPANDED_SYSCONFDIR@/dbus-1/system.conf". By creating 
additional configuration files and using the \-\-config-file option,
additional special-purpose message bus daemons could be created.

.PP
The systemwide daemon is normally launched by an init script, 
standardly called simply "messagebus". 

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

.PP
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).

.PP
There is no way to cause the D-BUS daemon to reload its configuration
file (HUP will not do so). The reason is that changing configuration
would break the semantics expected by applications connected to the
message bus. Thus, changing configuration would require kicking all
apps off the bus; so you may as well just restart the daemon.

.SH OPTIONS
The following options are supported:
.TP
.I "--config-file=FILE"
Use the given configuration file.
.TP
.I "--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.
.TP
.I "--print-address[=DESCRIPTOR]"
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.
.TP
.I "--print-pid[=DESCRIPTOR]"
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.
.TP
.I "--session"
Use the standard configuration file for the per-login-session message
bus.
.TP
.I "--system"
Use the standard configuration file for the systemwide message bus.
.TP
.I "--version"
Print the version of the daemon.

.SH CONFIGURATION FILE

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.

.PP
The configuration file also establishes resource limits, security
parameters, and so forth.

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

.PP
The standard systemwide and per-session message bus setups are
configured in the files "@EXPANDED_SYSCONFDIR@/dbus-1/system.conf" and
"@EXPANDED_SYSCONFDIR@/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.

.PP
The configuration file is an XML document. It must have the following
doctype declaration:
.nf

   <!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
    "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">

.fi

.PP
The following elements may be present in the configuration file.

.TP
.I "<busconfig>"
 
.PP
Root element.

.TP
.I "<type>"

.PP
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).

.PP
Example: <type>session</type>

.TP
.I "<include>"
 
.PP  
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.

.PP
<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.

.TP
.I "<includedir>"

.PP
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.

.PP
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
@EXPANDED_SYSCONFDIR@/dbus-1/system.d that allowed all apps to receive
this message and allowed the printer daemon user to send it.

.TP
.I "<user>"

.PP
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.

.PP
The last <user> entry in the file "wins", the others are ignored.

.PP
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.

.TP
.I "<fork>"
    
.PP
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.

.TP
.I "<listen>"

.PP
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.

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

.PP
If there are multiple <listen> elements, then the bus listens 
on multiple addresses. The bus will pass its address to 
activated 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.

.TP
.I "<auth>"

.PP
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.
    
.PP
Example: <auth>EXTERNAL</auth>

.PP
Example: <auth>DBUS_COOKIE_SHA1</auth>

.TP
.I "<servicedir>"

.PP
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).

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

.TP
.I "<limit>"

.PP
<limit> establishes a resource limit. For example:
.nf
  <limit name="max_message_size">64</limit>
  <limit name="max_completed_connections">512</limit>
.fi

.PP
The name attribute is mandatory.
Available limit names are:
.nf
      "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
                                     bytes
      "activation_timeout"         : milliseconds (thousandths) until 
                                     an activated service has to connect
      "auth_timeout"               : milliseconds (thousandths) a
                                     connection is given to
                                     authenticate
      "max_completed_connections"  : max number of authenticated connections  
      "max_incomplete_connections" : max number of unauthenticated
                                     connections
      "max_connections_per_user"   : max number of completed connections from
                                     the same user
      "max_pending_activations"    : max number of activations in
                                     progress at the same time
      "max_services_per_connection": max number of services a single 
                                     connection can own
.fi

.PP
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.

.PP
max_completed_connections divided by max_connections_per_user is the
number of users that can work together to DOS all other users by using
up all connections.

.TP
.I "<policy>"

.PP
The <policy> element defines a policy to be applied to a particular
set of connections to the bus. A policy is made up of
<allow> and <deny> elements.

.PP
The <policy> element has one of three attributes:
.nf
  context="(default|mandatory)"
  user="username or userid"
  group="group name or gid"
.fi

.PP
 
Policies are applied to a connection as follows:
.nf
   - 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 context="mandatory" policies are applied
.fi

.PP
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.

.TP
.I "<deny>"
.I "<allow>"

.PP
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.

.PP
The possible attributes of these elements are:
.nf
   send_interface="interface_name"
   send_member="method_or_signal_name" 
   send_error="error_name" 
   send_destination="service_name" 
   send_type="method_call" | "method_return" | "signal" | "error" 
   send_path="/path/name"

   receive_interface="interface_name"
   receive_member="method_or_signal_name" 
   receive_error="error_name" 
   receive_sender="service_name" 
   receive_type="method_call" | "method_return" | "signal" | "error"
   receive_path="/path/name"
   
   eavesdrop="true" | "false"

   own="servicename"
   user="username"
   group="groupname"
.fi

.PP
Examples:
.nf
   <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"/>
.fi

.PP
The <deny> 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).

.PP
send_destination and receive_sender rules mean that messages may not be
sent to or received from the *owner* of the given service, not that
they may not be sent *to that service 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.

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

.PP
"Eavesdropping" occurs when an application receives a message that
was explicitly addressed to a service the application does not own.
Eavesdropping thus only applies to messages that are addressed to
services (i.e. it does not apply to signals).

.PP
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
receive rules (with receive_* attributes).

.PP
user and group denials mean that the given user or group may 
not connect to the message bus.

.PP
For "service_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.

.PP
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.

.PP
A single <deny> rule may specify combinations of attributes such as
send_service 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_service="foo.blah"/> would
deny messages of the given interface AND to the given service.
To get an OR effect you specify multiple <deny> rules.

.PP
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.

.PP
Be careful with send_interface/receive_interface, because the 
interface field in messages is optional.

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

.SH BUGS
Please send bug reports to the D-BUS mailing list or bug tracker,
see http://www.freedesktop.org/software/dbus/