systemd A monkey with a typewriter Zbigniew Jędrzejewski-Szmek zbyszek@in.waw.pl sd_bus_default 3 sd_bus_default sd_bus_default_user sd_bus_default_system sd_bus_open sd_bus_open_user sd_bus_open_system sd_bus_open_system_remote sd_bus_open_system_machine Acquire a connection to a system or user bus #include <systemd/sd-bus.h> int sd_bus_default sd_bus **bus int sd_bus_default_user sd_bus **bus int sd_bus_default_system sd_bus **bus int sd_bus_open sd_bus **bus int sd_bus_open_user sd_bus **bus int sd_bus_open_system sd_bus **bus int sd_bus_open_system_remote sd_bus **bus const char *host int sd_bus_open_system_machine sd_bus **bus const char *machine sd_bus_default() acquires a bus connection object to the user bus when invoked in user context, or to the system bus otherwise. The connection object is associated to the calling thread. Each time the function is invoked from the same thread the same object is returned, but its reference count is increased by one, as long as at least one reference is kept. When the last reference to the connection is dropped (using the sd_bus_unref3 call), the connection is terminated. Note that the connection is not automatically terminated when the associated thread ends. It is important to drop the last reference to the bus connection explicitly before the thread ends or otherwise the connection will be leaked. sd_bus_default_user() returns a user bus connection object associated to the calling thread. sd_bus_default_system() is similar, but connects to the system bus. Note that sd_bus_default() is identical to these two calls, depending on the execution context. sd_bus_open() creates a new, independent bus connection to the user bus when invoked in user context, or the system bus otherwise. sd_bus_open_user() is similar, but connects only to the user bus. sd_bus_open_system() does the same, but connects to the system bus. In contrast to sd_bus_default(), sd_bus_default_user(), sd_bus_default_system() these calls return new, independent connection objects that are not associated with the invoking thread and are not shared between multiple invocations. It is recommended to share connections per thread to efficiently make use the available resources. Thus, it is recommended to use sd_bus_default(), sd_bus_default_user(), sd_bus_default_system() to connect to the user or system buses. If the $DBUS_SESSION_BUS_ADDRESS environment variable is set (cf. environ7), it will be used as the address of the user bus. This variable can contain multiple addresses separated by ;. If this variable is not set, a suitable default for the default user D-Bus instance will be used. If the $DBUS_SYSTEM_BUS_ADDRESS environment variable is set, it will be used as the address of the system bus. This variable uses the same syntax as $DBUS_SESSION_BUS_ADDRESS. If this variable is not set, a suitable default for the default system D-Bus instance will be used. sd_bus_open_system_remote() connects to the system bus on the specified host using ssh1. host consists of an optional user name followed by the @ symbol, and the hostname. sd_bus_open_system_machine() connects to the system bus in the specified machine, where machine is the name of a local container. See machinectl1 for more information about the "machine" concept. Note that connections into local containers are only available to privileged processes at this time. These calls allocate a bus connection object and initiate the connection to a well-known bus of some form. An alternative to using these high-level calls is to create an unconnected bus object with sd_bus_new3 and to connect it with sd_bus_start3. On success, these calls return 0 or a positive integer. On failure, these calls return a negative errno-style error code. The functions sd_bus_open(), sd_bus_open_user(), sd_bus_open_system(), sd_bus_open_system_remote(), and sd_bus_open_system_machine() return a new object and the caller owns the sole reference. When not needed anymore, this reference should be destroyed with sd_bus_unref3. The functions sd_bus_default(), sd_bus_default_user() and sd_bus_default_system() do not necessarily create a new object, but increase the connection reference by one. Use sd_bus_unref3 to drop the reference. Queued messages also keep a reference to the bus. For this reason, just because no application is having a reference to the bus does not mean that the bus object will be destroyed. Until all the messages are sent, the bus object will stay alive. sd_bus_flush can be used to send all the queued messages so they drop their references. Returned errors may indicate the following problems: -EINVAL The specified parameters are invalid. -ENOMEM Memory allocation failed. -ESOCKTNOSUPPORT The protocol version required to connect to the selected bus is not supported. In addition, any further connection-related errors may be by returned. See sd_bus_send3. sd_bus_open_user() and the other functions described here are available as a shared library, which can be compiled and linked to with the libsystemd pkg-config1 file. systemd1, sd-bus3, sd_bus_new3, sd_bus_ref3, sd_bus_unref3, ssh1, systemd-machined.service8, machinectl1