dbus-daemon(3) C Library Functions dbus-daemon(3)NAMEdbus-daemon - Message bus daemon
SYNOPSISdbus-daemon [--config-file=file] [--fork | --nofork] [--introspect]
[--print-address[=descriptor]] [--print-pid[=descriptor]] [--session]
[--system] [--version]
DESCRIPTIONdbus-daemon is the D-Bus message bus daemon. 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 dae‐
mon and can exchange messages with one another.
There are two standard message bus instances. dbus-daemon is used for
both of these instances, but with a different configuration file.
· systemwide message bus - Launched when the system is started and
is enabled by default. Additional systemwide services can be
launched via D-Bus service activation However, D-Bus service
activation is disabled on Solaris. Note that the --system option
is equivalent to:
"--config-file=/etc/dbus-1/system.conf"
· per-user-login-session message bus - Launched each time a user
logs in. Note that the --session option is equivalent to:
"--config-file=/etc/dbus-1/session.conf"
By creating additional configuration files and using the --config-file
option, additional special-purpose message bus daemons could be cre‐
ated.
On Solaris, D-Bus is configured with service activation disabled, so
that users cannot launch systemwide D-Bus services on demand. This
feature is not used by any applications that are currently shipped with
Solaris.
On Solaris, the D-Bus service is managed by the smf(5) service manage‐
ment facility under the service identifier svc:/system/dbus. On
Solaris, it is recommended that you use the svcadm(1m) utility to start
and stop the D-Bus service
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 config‐
uration changes would require kicking all applications off the bus; so
they will only take effect if you restart the daemon. Policy changes
should take effect with SIGHUP.
OPTIONS
The following options are supported:
--config-file=file
Use the given configuration file.
--fork
Force the message bus to fork and become a daemon, regardless of
configuration file settings.
--introspect
Print introspect data and exit.
--nofork
Avoid running the message bus as a daemon, regardless of configura‐
tion file settings.
--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.
--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.
--session
Use the standard configuration file for the per-login-session mes‐
sage bus.
--system
Use the standard configuration file for the systemwide message bus.
--version
Print the version of the daemon.
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables:
DBUS_SESSION_BUS_ADDRESS
The address of the login session message bus. If this variable is
not set, applications may also try to read the address from the X
Window System root window property _DBUS_SESSION_BUS_ADDRESS. The
root window property must have type STRING. The environment vari‐
able should have precedence over the root window property.
DBUS_STARTER_BUS_TYPE
If the well-known type of the message bus is "session", then this
environment variable will be set to "session". If the type of the
message bus is "system;", then this environment variable will be
set to "system".
DBUS_VERBOSE
Set DBUS_VERSION=1 to enable debugging, if D-Bus was compiled with
verbose debug mode enabled.
EXIT STATUS
The following exit values are returned:
0 Application exited successfully
>0 Application exited with failure
EXTENDED DESCRIPTION
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.
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"
"http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
The following elements may be present in the configuration file.
<busconfig>
Root element.
<type>
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
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 vari‐
able will be set to the address of the system bus (which is normally
well known anyway).
Example: <type>session</type>
<include>
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
is a fatal error for the included file to be absent.
<includedir>
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 applications to receive this mes‐
sage and allowed the printer daemon user to send it.
<user>
The user account the daemon should run as, specified as either a user‐
name 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.
<fork>
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.
<keep_umask>
If present, the bus daemon keeps its original umask when forking. This
may be useful to avoid affecting the behavior of child processes.
<listen>
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 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, applications 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>
<auth>
Lists permitted authorization mechanisms. If this element does not
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>
<servicedir>
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/>
<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" should be found at
http://freedesktop.org/wiki/Standards/basedir-spec.
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/>
<standard_system_servicedirs/> specifies the standard systemwide 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/>
<servicehelper/> specifies the setuid helper that is used to launch
system daemons with an alternate user. Typically this would be the
dbus-daemon-launch-helper executable. Because D-Bus service activation
is disabled on Solaris, the dbus-daemon-launch-helper executable is not
distributed with Solaris.
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 con‐
figuration file would probably be nonsense.
<limit>
<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" : maximum size of a
single message in bytes
"service_start_timeout" : milliseconds
(thousandths) until a
started service has to
connect
"auth_timeout" : milliseconds
(thousandths) a
connection is given to
authenticate
"max_completed_connections" : maximum number of
authenticated
connections
"max_incomplete_connections" : maximum number of
unauthenticated
connections
"max_connections_per_user" : maximum number of
completed connections
from the same user
"max_pending_service_starts" : maximum number of
service launches in
progress at the same
time
"max_names_per_connection" : maximum number of
names a single
connection can own
"max_match_rules_per_connection" : maximum number of
match rules for a
single connection
"max_replies_per_connection" : maximum number of
pending method replies
per connection (number
of calls-in-progress)
"reply_timeout" : milliseconds
(thousandths) until a
method call times out
The maximum incoming/outgoing queue sizes allow a new message to be
queued if one byte remains below the maximum. So you can in fact
exceed the maximum 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.
<policy>
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:
· context="(default|mandatory)"
· at_console="(true|false)"
· 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 unde‐
fined 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> and <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_interface="interface_name"
send_member="method_or_signal_name"
send_error="error_name"
send_destination="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="name"
receive_type="method_call" | "method_return" | "signal" | "error"
receive_path="/path/name"
send_requested_reply="true" | "false"
receive_requested_reply="true" | "false"
eavesdrop="true" | "false"
own="name"
user="username"
group="groupname"
Examples:
<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
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 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 sub‐
stituted, meaning "any". Complex globs like "foo.bar.*" are not
allowed for now because they would 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 not 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_interface="org.foo.Bar" send_destination="org.foo.Service"/>
<selinux>
The <selinux> element contains settings related to Security Enhanced
Linux. More details below. Note, SELinux is not supported on Solaris.
<associate>
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 is 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.
SELinux
SELinux is not supported on Solaris.
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 secu‐
rity attributes, known as a security context. A security con‐
text 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 pro‐
vide 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 opera‐
tions 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
"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 are assuming that only UNIX domain sockets
will be used to connect to the systemwide bus. If this changes, we will
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 "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.
DEBUGGING
If you are trying to figure out where your messages are going or why
you are not getting messages, there are several things you can try.
Remember that the system bus is heavily locked down and if you have not
installed a security policy file to allow your message through, it will
not work. For the session bus, this is not a concern.
The simplest way to figure out what is happening on the bus is to run
the dbus-monitor(1) program, which comes with the D-Bus package. You
can also send test messages with dbus-send(1). 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 dae‐
mon.)
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.
EXAMPLES
Example 1: Message bus daemon
example% dbus-daemonFILES
The following files are used by this application:
/usr/lib/dbus-daemon
Executable for dbus-daemon
/usr/share/dbus-1/services
Directory containing standard D-Bus session services.
/usr/share/dbus-1/system-services
Directory containing standard D-Bus systemwide services.
/etc/dbus-1/session.conf
Configuration file for D-Bus session services.
/etc/dbus-1/system.conf
Configuration file for D-Bus system services.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │system/library/dbus │
├─────────────────────────────┼─────────────────────────────┤
│Interface stability │Volatile │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSO
More information can be found at:
http://www.freedesktop.org/software/dbus/
dbus-binding-tool(1), dbus-cleanup-sockets(1), dbus-launch(1), dbus-
monitor(1), dbus-send(1), dbus-uuidgen(1), svcadm(1m), libdbus-
glib-1(3), attributes(5), environ(5), smf(5)NOTES
For authorship information refer to http://www.freedesktop.org/soft‐
ware/dbus/doc/AUTHORS. Updated by Brian Cameron, Sun Microsystems
Inc., 2007.
Please send bug reports to the D-Bus mailing list or bug tracker, see
http://www.freedesktop.org/software/dbus/
SunOS 5.11 25 Feb 2009 dbus-daemon(3)
