Dbus daemon linux что это



Dbus daemon linux что это

D-BUS является системой шины сообщений, предлагающей приложениям простой способ обмена сообщениями. В составе D-BUS есть как системный демон (для таких событий, как «добавлено новое устройство» или «изменена очередь печати»), так и демон, запускаемый при регистрации в системе каждой новой сессии пользователя (для обычного межпроцессного обмена сообщениями между приложениями пользователя). Кроме того, шина сообщений собирается поверх фреймворка, предназначенного для передачи сообщений вида 1:1 и который может использоваться любыми двумя приложениям для непосредственного взаимодействия друг с другом (минуя демон шины обмена сообщениями).

Известно, что пакет правильно собирается и работает на платформе LFS-7.0.

Информация о пакете

  • Загрузка (HTTP): http://dbus.freedesktop.org/releases/dbus/dbus-1.4.16.tar.gz
  • Контрольная сумма MD5: MD5: 44a2a10678e7e50460879c3eb4453a65
  • Размер загружаемого пакета: 1,8 MB
  • Оценочный размер требуемого дискового пространства: 83 MB
  • Оценочное время сборки: 0,5 SBU

Зависимости пакета D-BUS

Обязательные

Необязательные

Xorg Libraries, D-Bus GLib Bindings-0.98 (для запуска тестов) и Doxygen-1.7.2 (для создания документации по API)

Обратите внимание, что скрипт configure похож на скрипт пакета xmlto-0.0.23, но ничего не делает, т.к. документация XML/HTML уже есть в дереве с исходным кодом.

Конфигурирование ядра

Обеспечьте, чтобы следующий параметр был включен в конфигурации ядра, и перекомпилируйте ядро, если это необходимо:

Установка пакета D-BUS

В роли пользователя root создайте системного пользователя и группу, предназначенные для доступа к шине системных сообщений:

Установите пакет D-BUS с помощью следующих команд (вы, возможно, сначала захотите с помощью команды ./configure —help посмотреть общее описание и добавить к команде configure, представленной ниже, все необходимые параметры):

Инструкции по тестированию приведены ниже.

Теперь в роли пользователя root выполните:

Набор тестов для этого пакета запустить не удастся, если не будет установлен пакет D-Bus GLib Bindings-0.98 . Тесты требуют передачи дополнительных параметров в скрипт configure и обращения к дополнительным функциям двоичных модулей. Такой интерфейс не предназначен для выполнения сборки пакета D-BUS. Если вы хотите запускать тесты для каждого модуля, выполните следующие команды:

Обратите внимание, что если тесты запускаются внутри оболочки Midnight Commander, будет выдано сообщение о том, что они, возможно, не прошли.

Пояснение команд

—libexecdir=/usr/lib/dbus-1.0 : Указывает, что устанавливаться будут только те двоичные файлы, которые используется только пакетом D-BUS, а директорий dbus-1 будет помещен в /usr/lib/dbus-1.0 , а не в /usr/libexec .

—localstatedir=/var : Этот параметр указывает, что файл PID демона, сокет системной шины и файл uuid машины будут созданы в директории /var , а не в директории /usr/var .

—enable-tests : Строит дополнительные пути, используемые при тестировании кода. Конфигурирование заканчивается выдачей замечания, сообщающего об этом.

—enable-asserts : Включает отладочный код, выполняющий проверку инструкций, которые, как предполагается, должны быть истинными. В результате будет предотвращена выдача предупреждения, создаваемого параметром ‘ —enable-tests ‘, которое только указывает, что тесты завершились, и не сообщает о действительных результатах прохождения всех тестов. Однако данный параметр добавит свое собственное сообщение, на которое не следует обращать внимание при сборке пакета.

—disable-static : Предотвращает сборку и установку статических библиотек.

Конфигурирование пакета dbus

Конфигурационные файлы

/etc/dbus-1/session.conf , /etc/dbus-1/system.conf и /etc/dbus-1/system.d/*

Подробнее о конфигурировании

Конфигурационные файлы, указанные выше, по-видимому, менять не нужно. Если изменения необходимы, вы должны создать файл /etc/dbus-1/session-local.conf и/или файл /etc/dbus-1/system-local.conf и внести в них необходимые изменения.

Если в каком-нибудь другом пакете файл .service , используемый D-Bus, устанавливается не в стандартный директорий /usr/share/dbus-1/services , то директорий, куда устанавливается этот файл, нужно добавить в конфигурацию текущей сессии. Например, директорий /usr/local/share/dbus-1/services можно добавить в роли пользователя root с помощью следующих команд:

Загрузочный скрипт

Чтобы в процессе перезагрузки системы автоматически запускать команду dbus-daemon, установите загрузочный скрипт /etc/rc.d/init.d/dbus , имеющийся в пакете blfs-bootscripts-20111226.

Заметим, что это в загрузочном скрипте запускается только общесистемный демон D-BUS. Каждому пользователю, которому требуется доступ к сервисам D-BUS, нужно будет также запустить сессионный демон. Есть много вариантов запуска сессионного демона с помощью команды dbus-launch. Подробности об имеющихся параметрах и возможностях смотрите на странице man команды dbus-launch. Вот некоторые предложения и примеры:

    Добавьте в файл

/.xinitrc строчку с командой dbus-launch в строку файла

/.xinitrc , которая будет запускать графическую среду вашего рабочего стола; смотрите раздел «Конфигурирование базовых пакетов GNOME».
Если вы пользуетесь менеджером xdm или каким-либо другим менеджер дисплеев, в котором происходит обращение к файлу

/.xsession , вы можете добавить в ваш файл

/.xsession строчку с командой dbus-launch, которая будет запускать графическую среду вашего рабочего стола. Синтаксис аналогичен примеру, приведенному в файле

/.xinitrc .

  • Если вы пользуетесь менеджером gdm или каким-либо другим менеджер дисплеев, в котором для инициализации сессии применяются настроечные файлы, воспользуйтесь примером, приведенным в разделе «Подробнее о конфигурировании» и описывающим инструкции GDM по созданию файла с командой dbus-launch.
  • В примерах, приведенных ранее, используется команда dbus-launch, указывающая программу, которая должна быть запущена. Преимущество этого подхода в том (когда также используется параметр —exit-with-session ), что в случае, когда указанная программа будет остановлена, сессионный демон будет также остановлен. Для запуска сессионного демона добавьте или в ваши системные или персональные скрипты запуска следующие строки:

    В этом случае сессионый демон не останавливается, когда вы выходите из командной оболочки, так что вы должны в ваш файл

    /.bash_logout добавить следующую строку:

  • Написана рекомендация, в которой предлагаются способы запуска скриптов с помощью сессионного менеджера KDM, имеющемся в рабочем столе KDE. Идеи, изложенные в этой рекомендации, возможно, удастся использовать также и с другими сессионными менеджерами. С рекомендацией можно ознакомиться по ссылке http://www.linuxfromscratch.org/hints/downloads/files/execute-session-scripts-using-kdm.txt t.
  • Описание пакета

    Установленные программы: dbus-cleanup-sockets, dbus-daemon, dbus-daemon-launch-helper, dbus-launch, dbus-monitor, dbus-send, and dbus-uuidgen

    Установленные библиотеки: libdbus-1.

    используется для очистки директория от остатков сокетов

    является демоном шины сообщений D-BUS

    используется для запуска dbus-daemon из скрипта командной оболочки. Как правило, вызывается из скриптов, регистрирующих вход пользователей в систему

    используется для мониторинга сообщений, поступающих через шину сообщений D-BUS

    используется для отправки сообщения в шину сообщений D-BUS

    используется для создания или чтения универсального уникального идентификатора

    содержит функции API, используемые демоном сообщений D-BUS. D-BUS является первой библиотекой, в которой предложены средства обмена сообщениями вида 1:1 между двумя любыми приложениями; dbus-daemon является приложением, использующим эту библиотеку для реализации демона шины сообщений

    Перевод сделан с варианта оригинала, датированного 2011-12-16 19:54:18 +0000

    Источник

    SYNOPSIS

    dbus-daemon [—version] [—session] [—system] [—config-file=FILE] [—print-address [=DESCRIPTOR]] [—print-pid [=DESCRIPTOR]] [—fork] [—nosyslog] [—syslog] [—syslog-only] [—ready-event-handle=value]

    DESCRIPTION

    dbus-daemon 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; 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 different configuration file.

    The —session option is equivalent to «—config-file=/usr/share/dbus-1/session.conf» and the —system option is equivalent to «—config-file=/usr/share/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, standardly 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 configuration file and to flush its user/group information caches. Some configuration 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.

    OPTIONS

    The following options are supported:

    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 specification and its backward compatibility is not guaranteed; this document is documentation, not specification.

    The standard systemwide and per-session message bus setups are configured in the files «/usr/share/dbus-1/system.conf» and «/usr/share/dbus-1/session.conf». These files normally a system-local.conf or session-local.conf in /etc/dbus-1; you can put local overrides in those files to avoid modifying the primary configuration files.

    The standard system bus normally reads additional XML files from /usr/share/dbus-1/system.d. Third-party packages should install the default policies necessary for correct operation into that directory, which has been supported since dbus 1.10 (released in 2015).

    The standard system bus normally also reads XML files from /etc/dbus-1/system.d, which should be used by system administrators if they wish to override default policies.

    Third-party packages would historically install XML files into /etc/dbus-1/system.d, but this practice is now considered to be deprecated: that directory should be treated as reserved for the system administrator.

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

    The following elements may be present in the configuration file.

    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). 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_SYSTEM_BUS_ADDRESS environment variable will be set to the address of the system bus (which is normally well known anyway).

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

    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 foo.d 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 notification of printer queue changes, it could install a file to /usr/share/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 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.

    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.

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

    If present, the bus daemon will log to syslog. The —syslog, —syslog-only and —nosyslog command-line options take precedence over this setting.

    If present, the bus daemon will write its pid to the specified file. The —nopidfile command-line option takes precedence over this setting.

    If present, connections that authenticated using the ANONYMOUS mechanism will be authorized to connect. This option has no practical effect unless the ANONYMOUS mechanism has also been enabled using the element, described below.

    Using this directive in the configuration of the well-known system bus or the well-known session bus will make that bus insecure and should never be done. Similarly, on custom bus types, using this directive will usually make the custom bus insecure, unless its configuration has been specifically designed to prevent anonymous users from causing damage or escalating privileges.

    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.

    On platforms other than Windows, unix-based transports (unix, systemd, launchd) are the default for both the well-known system bus and the well-known session bus, and are strongly recommended.

    On Windows, unix-based transports are not available, so TCP-based transports must be used. Similar to remote X11, the tcp and nonce-tcp transports have no integrity or confidentiality protection, so they should normally only be used across the local loopback interface, for example using an address like tcp:host=127.0.0.1 or nonce-tcp:host=localhost. In particular, configuring the well-known system bus or the well-known session bus to listen on a non-loopback TCP address is insecure.

    Developers are sometimes tempted to use remote TCP as a debugging tool. However, if this functionality is left enabled in finished products, the result will be dangerously insecure. Instead of using remote TCP, developers should relay connections via Secure Shell or a similar protocol[1].

    Remote TCP connections were historically sometimes used to share a single session bus between login sessions of the same user on different machines within a trusted local area network, in conjunction with unencrypted remote X11, a NFS-shared home directory and NIS (YP) authentication. This is insecure against an attacker on the same LAN and should be considered strongly deprecated; more specifically, it is insecure in the same ways and for the same reasons as unencrypted remote X11 and NFSv2/NFSv3. The D-Bus maintainers recommend using a separate session bus per (user, machine) pair, only accessible from within that machine.

    If there are multiple

  • elements, then the bus listens on multiple addresses. The bus will pass its address to started services or other interested parties with the last address given in
  • first. That is, apps will try to connect to the last
  • 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

    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 system. 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.

    tcp/nonce-tcp addresses also allow a bind=hostname option, used in a listenable address to configure the interface on which the server will listen: either the hostname is the IP address of one of the local machine’s interfaces (most commonly 127.0.0.1), a DNS name that resolves to one of those IP addresses, ‘0.0.0.0’ to listen on all IPv4 interfaces simultaneously, or ‘::’ to listen on all IPv4 and IPv6 interfaces simultaneously (if supported by the OS). If not specified, the default is the same value as «host».

    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.

    On non-Windows operating systems, allowing only the EXTERNAL authentication mechanism is strongly recommended. This is the default for the well-known system bus and for the well-known session bus.

    Adds a directory to search for .service files, which tell the dbus-daemon how to start a program to provide a particular well-known bus name. See the D-Bus Specification for more details about the contents of .service files.

    If a particular service is found in more than one , the first directory listed in the configuration file takes precedence. If two service files providing the same well-known bus name are found in the same directory, it is arbitrary which one will be chosen (this can only happen if at least one of the service files does not have the recommended name, which is its well-known bus name followed by «.service»).

    requests a standard set of session service directories. Its effect is similar to specifying a series of elements for each of the data directories, in the order given here. It is not exactly equivalent, because there is currently no way to disable directory monitoring or enforce strict service file naming for a .

    As with elements, if a particular service is found in more than one service directory, the first directory takes precedence. If two service files providing the same well-known bus name are found in the same directory, it is arbitrary which one will be chosen (this can only happen if at least one of the service files does not have the recommended name, which is its well-known bus name followed by «.service»).

    On Unix, the standard session service directories are:

    Unlike the other standard session service directories, this directory enforces strict naming for the service files: the filename must be exactly the well-known bus name of the service, followed by «.service».

    Also unlike the other standard session service directories, this directory is never monitored with inotify(7) or similar APIs. Programs that create service files in this directory while a dbus-daemon is running are expected to call the dbus-daemon’s ReloadConfig() method after they have made changes.

    /.local/share (see the XDG Base Directory Specification): this location is specified by the D-Bus Specification, and is suitable for per-user, locally-installed software.

    /.local/share/flatpak/exports/share/ and /var/lib/flatpak/exports/share/ when flatpak(1) is used.

    The «XDG Base Directory Specification» can be found at http://freedesktop.org/wiki/Standards/basedir-spec if it hasn’t moved, otherwise try your favorite search engine.

    On Windows, the standard session service directories are:

    The 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.

    specifies the standard system-wide activation directories that should be searched for service files. As with session services, the first directory listed has highest precedence.

    On Unix, the standard system service directories are:

    On Windows, there is no standard system bus, so there are no standard system bus directories either.

    The option is only relevant to the per-system bus daemon defined in /usr/share/dbus-1/system.conf. Putting it in any other configuration file would probably be nonsense.

    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 option is only relevant to the per-system bus daemon defined in /usr/share/dbus-1/system.conf. Putting it in any other configuration file would probably be nonsense.

    establishes a resource limit. For example:

    The name attribute is mandatory. Available limit names are:

    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.

    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.

    Currently, the system bus has a default-deny policy for sending method calls and owning bus names, and a default-allow policy for receiving messages, sending signals, and sending a single success or error reply for each method call that does not have the NO_REPLY flag. Sending more than the expected number of replies is not allowed.

    In general, it is best to keep system services as small, targeted programs which run in their own process and provide a single bus name. Then, all that is needed is an 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.

    element has one of four attributes:

    Policies are applied to a connection as follows:

    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.

    A element appears below a

    The possible attributes of these elements are:

    The 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).

    Rules with one or more of the send_* family of attributes are checked in order when a connection attempts to send a message. The last rule that matches the message determines whether it may be sent. The well-known session bus normally allows sending any message. The well-known system bus normally allows sending any signal, selected method calls to the dbus-daemon, and exactly one reply to each previously-sent method call (either success or an error). Either of these can be overridden by configuration; on the system bus, services that will receive method calls must install configuration that allows them to do so, usually via rules of the form

    Rules with one or more of the receive_* family of attributes, or with the eavesdrop attribute and no others, are checked for each recipient of a message (there might be more than one recipient if the message is a broadcast or a connection is eavesdropping). The last rule that matches the message determines whether it may be received. The well-known session bus normally allows receiving any message, including eavesdropping. The well-known system bus normally allows receiving any message that was not eavesdropped (any unicast message addressed to the recipient, and any broadcast message).

    The eavesdrop, min_fds and max_fds attributes are modifiers that can be applied to either send_* or receive_* rules, and are documented below.

    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. As a special case, send_destination=»*» matches any message (whether it has a destination specified or not), and receive_sender=»*» similarly matches any message.

    Rules with send_broadcast=»true» match signal messages with no destination (broadcasts). Rules with send_broadcast=»false» are the inverse: they match any unicast destination (unicast signals, together with all method calls, replies and errors) but do not match messages with no destination (broadcasts). This is not the same as send_destination=»*», which matches any sent message, regardless of whether it has a destination or not.

    The other send_* and receive_* attributes are purely textual/by-value matches against the given field in the message header, except that for the attributes where it is allowed, * matches any message (whether it has the relevant header field or not). For example, send_interface=»*» matches any sent message, even if it does not contain an interface header field. More complex glob matching such as foo.bar.* is not allowed.

    «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 , [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.

    The min_fds and max_fds attributes modify either send_* or receive_* rules. A rule with the min_fds attribute only matches messages if they have at least that many Unix file descriptors attached. Conversely, a rule with the max_fds attribute only matches messages if they have no more than that many file descriptors attached. In practice, rules with these attributes will most commonly take the form , or .

    Rules with the user or group attribute are checked when a new connection to the message bus is established, and control whether the connection can continue. Each of these attributes cannot be combined with any other attribute. As a special case, both user=»*» and group=»*» match any connection. If there are no rules of this form, the default is to allow connections from the same user ID that owns the dbus-daemon process. The well-known session bus normally uses that default behaviour, while the well-known system bus normally allows any connection.

    Rules with the own or own_prefix attribute are checked when a connection attempts to own a well-known bus names. As a special case, own=»*» matches any well-known bus name. The well-known session bus normally allows any connection to own any name, while the well-known system bus normally does not allow any connection to own any name, except where allowed by further configuration. System services that will own a name must install configuration that allows them to do so, usually via rules of the form

    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.

    A single 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. would deny messages with the given interface AND the given bus name. To get an OR effect you specify multiple 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 ! 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:

    The element contains settings related to Security Enhanced Linux. More details below.

    This means that if a connection asks to own the name «org.freedesktop.Foobar» then the source context will be the context of the connection 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:

    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.

    The default mode is «enabled». In «enabled» mode, AppArmor mediation will be performed if AppArmor support is available in the kernel. If it is not available, dbus-daemon will start but AppArmor mediation will not occur. In «disabled» mode, AppArmor mediation is disabled. In «required» mode, AppArmor mediation will be enabled if AppArmor support is available, otherwise dbus-daemon will refuse to start.

    The AppArmor mediation mode of the bus cannot be changed after the bus starts. Modifying the mode in the configuration file and sending a SIGHUP signal to the daemon has no effect on the mediation mode.

    INTEGRATING SESSION SERVICES

    Integration files are not mandatory for session services: any program with access to the session bus can request a well-known name and provide D-Bus interfaces.

    Many D-Bus session services support service activation, a mechanism in which the dbus-daemon can launch the service on-demand, either by running the session service itself or by communicating with systemd —user. This is set up by creating a service file in the directory $ /dbus-1/services, for example:

    See the D-Bus Specification[2] for details of the contents and interpretation of service files.

    If there is a service file for com.example.SessionService1, it should be named com.example.SessionService1.service, although for compatibility with legacy services this is not mandatory.

    Session services that declare the optional SystemdService must also provide a systemd user service unit file whose name or Alias matches the SystemdService (see systemd.unit(5), systemd.service(5) for further details on systemd service units), for example:

    INTEGRATING SYSTEM SERVICES

    The standard system bus does not allow method calls or owning well-known bus names by default, so a useful D-Bus system service will normally need to configure a default security policy that allows it to work. D-Bus system services should install a default policy file in $ /dbus-1/service.d, containing the policy rules necessary to make that system service functional. A best-practice policy file will often look like this:

    where _example is the username of the system uid that will run the system service daemon process, and com.example.Example1 is its well-known bus name.

    The policy file for com.example.Example1 should normally be named com.example.Example1.conf.

    Some existing system services rely on more complex

    rules to control the messages that the service can receive. However, the dbus-daemon‘s policy language is not well-suited to finer-grained policies: any policy has to be expressed in terms of D-Bus interfaces and method names, not in terms of higher-level domain-specific concepts like removable or built-in devices. It is recommended that new services should normally accept method call messages from all callers, then apply a sysadmin-controllable policy to decide whether to obey the requests contained in those method call messages, for example by consulting polkit[3].

    Like session services, many D-Bus system services support service activation, a mechanism in which the dbus-daemon can launch the service on-demand, either by running the system service itself or by communicating with systemd. This is set up by creating a service file in the directory $ /dbus-1/system-services, for example:

    See the D-Bus Specification[2] for details of the contents and interpretation of service files.

    If there is a service file for com.example.Example1, it must be named com.example.Example1.service.

    System services that declare the optional SystemdService must also provide a systemd service unit file whose name or Alias matches the SystemdService (see systemd.unit(5), systemd.service(5) for further details on systemd service units), for example:

    SELINUX

    See http://www.nsa.gov/selinux/ for full details on SELinux. Some useful 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 particular subject or object that are relevant to the security policy.

    In order to better encapsulate security contexts and to provide 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 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 connection, the bus daemon will check permissions with the security context 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’re assuming that only UNIX domain sockets will be used to connect to the systemwide bus. If this changes, we’ll 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».

    APPARMOR

    The AppArmor confinement context is stored when applications connect to the bus. The confinement context consists of a label and a confinement mode. When a security decision is required, the daemon uses the confinement context to query the AppArmor policy to determine if the action should be allowed or denied and if the action should be audited.

    The daemon performs AppArmor security checks in three places.

    First, any time a message is routed from one connection to another connection, the bus daemon will check permissions with the label of the first connection as source, label and/or connection name of the second connection as target, along with the bus name, the path name, the interface name, and the member name. Reply messages, such as method_return and error messages, are implicitly allowed if they are in response to a message that has already been allowed.

    Second, any time a connection asks to own a name, the bus daemon will check permissions with the label of the connection as source, the requested name as target, along with the bus name.

    Third, any time a connection attempts to eavesdrop, the bus daemon will check permissions with the label of the connection as the source, along with the bus name.

    AppArmor rules for bus mediation are not stored in the bus configuration files. They are stored in the application’s AppArmor profile. Please see apparmor.d(5) for more details.

    DEBUGGING

    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:

    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 compiled 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.)

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