.\" .\" 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 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 .fi .PP The following elements may be present in the configuration file. .TP .I "" .PP Root element. .TP .I "" .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 element "wins" (previous values are ignored). .PP Example: session .TP .I "" .PP Include a file filename.conf at this point. If the filename is relative, it is located relative to the configuration file doing the including. .PP 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 "" .PP Include all files in foo.d 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 "" .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 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 "" .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 "" .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: unix:path=/tmp/foo .PP If there are multiple 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 first. That is, apps will try to connect to the last address first. .TP .I "" .PP Lists permitted authorization mechanisms. If this element doesn't exist, then all known mechanisms are allowed. If there are multiple elements, all the listed mechanisms are allowed. The order in which mechanisms are listed is not meaningful. .PP Example: EXTERNAL .PP Example: DBUS_COOKIE_SHA1 .TP .I "" .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 "" .PP establishes a resource limit. For example: .nf 64 512 .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 "" .PP The element defines a policy to be applied to a particular set of connections to the bus. A policy is made up of and elements. .PP The 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 "" .PP A element appears below a element and prohibits some action. The possible attributes of a element are: .nf send="messagename" receive="messagename" own="servicename" send_to="servicename" receive_from="servicename" user="username" group="groupname" .fi .PP Examples: .nf .fi .PP The 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_to and receive_from 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 user and group denials mean that the given user or group may not connect to the message bus. .PP For "servicename" or "messagename" or "username" or "groupname" 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 for a user or group; user/group denials can only be inside context="default" or context="mandatory" policies. .PP A single rule may specify both send and send_to, OR both receive and receive_from. In this case, the denial applies only if both attributes match the message being denied. e.g. would deny messages of the given name AND to the given service. .TP .I "" .PP Makes an exception to previous statements. Works just like but with the inverse meaning. .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/