sd_bus_emit_signal - Man Page

Convenience functions for emitting (standard) D-Bus signals


#include <systemd/sd-bus-vtable.h>

int sd_bus_emit_signal(sd_bus *bus, const char *path, const char *interface, const char *member, const char *types, ...);

int sd_bus_emit_signalv(sd_bus *bus, const char *path, const char *interface, const char *member, const char *types, va_list ap);

int sd_bus_emit_signal_to(sd_bus *bus, const char *destination, const char *path, const char *interface, const char *member, const char *types, ...);

int sd_bus_emit_signal_tov(sd_bus *bus, const char *destination, const char *path, const char *interface, const char *member, const char *types, va_list ap);

int sd_bus_emit_interfaces_added(sd_bus *bus, const char *path, const char *interface, ...);

int sd_bus_emit_interfaces_added_strv(sd_bus *bus, const char *path, const char **interfaces);

int sd_bus_emit_interfaces_removed(sd_bus *bus, const char *path, const char *interface, ...);

int sd_bus_emit_interfaces_removed_strv(sd_bus *bus, const char *path, const char **interfaces);

int sd_bus_emit_properties_changed(sd_bus *bus, const char *path, const char *interface, const char *name, ...);

int sd_bus_emit_properties_changed_strv(sd_bus *bus, const char *path, const char *interface, const char **names);

int sd_bus_emit_object_added(sd_bus *bus, const char *path);

int sd_bus_emit_object_removed(sd_bus *bus, const char *path);


sd_bus_emit_signal() is a convenience function for initializing a bus message object and emitting the corresponding D-Bus signal. It combines the sd_bus_message_new_signal(3), sd_bus_message_append(3) and sd_bus_send(3) functions into a single function call. sd_bus_emit_signalv() is equivalent to sd_bus_message_append(), except that it is called with a "va_list" instead of a variable number of arguments.

sd_bus_emit_signal_to() and sd_bus_emit_signal_tov() are identical to sd_bus_emit_signal() and sd_bus_emit_signalv(), except that they can emit the signal to a single destination. Give destination as NULL to broadcast the signal.

sd_bus_emit_interfaces_added() and sd_bus_emit_interfaces_removed() are used to implement the InterfacesAdded and InterfacesRemoved signals of the org.freedesktop.DBus.ObjectManager interface. They take a path whose interfaces have been modified as an argument and a variable list of interfaces that have been added or removed, respectively. The final argument passed to sd_bus_emit_interfaces_added() and sd_bus_emit_interfaces_removed() must be NULL. This allows both functions to safely determine the number of passed interface arguments. sd_bus_emit_interfaces_added_strv() and sd_bus_emit_interfaces_removed_strv() are identical to their respective counterparts but both take the list of interfaces as a single argument instead of a variable number of arguments.

sd_bus_emit_properties_changed() is used to implement the PropertiesChanged signal of the org.freedesktop.DBus.Properties interface. It takes an object path, interface and a variable list of property names as its arguments. The final argument passed to sd_bus_emit_properties_changed() must be NULL. This allows it to safely determine the number of passed property names. sd_bus_emit_properties_changed_strv() is identical to sd_bus_emit_properties_changed() but takes the list of property names as a single argument instead of a variable number of arguments.

sd_bus_emit_object_added() and sd_bus_emit_object_removed() are convenience functions for emitting the InterfacesAdded or InterfacesRemoved signals for all interfaces registered on a specific object path, respectively. This includes any parent fallback vtables if they are not overridden by a more applicable child vtable. It also includes all the standard D-Bus interfaces implemented by sd-bus itself on any registered object.

Note that sd_bus_emit_interfaces_added(), sd_bus_emit_interfaces_removed(), sd_bus_emit_object_added() and sd_bus_emit_object_removed() require an object manager to have been registered on the given object path or one of its parent object paths using sd_bus_add_object_manager(3).

Return Value

On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code.


Returned errors may indicate the following problems:


One of the required parameters is NULL or invalid. A reserved D-Bus interface was passed as the interface parameter.

Added in version 246.


The bus cannot be resolved.

Added in version 246.


The bus was created in a different process, library or module instance.

Added in version 246.


Memory allocation failed.

Added in version 246.


One of sd_bus_emit_interfaces_added(), sd_bus_emit_interfaces_removed(), sd_bus_emit_object_added() or sd_bus_emit_object_removed() was called on an object without an object manager registered on its own object path or one of its parent object paths.

Added in version 246.

See the man pages of sd_bus_message_new_signal(3), sd_bus_message_append(3) and sd_bus_send(3) for more possible errors.


Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd pkg-config(1) file.

The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call setenv(3) from a parallel thread. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started.


sd_bus_emit_signal(), sd_bus_emit_signalv(), sd_bus_emit_interfaces_added(), sd_bus_emit_interfaces_added_strv(), sd_bus_emit_interfaces_removed(), sd_bus_emit_interfaces_removed_strv(), sd_bus_emit_properties_changed(), sd_bus_emit_properties_changed_strv(), sd_bus_emit_object_added(), and sd_bus_emit_object_removed() were added in version 246.

sd_bus_emit_signal_to() and sd_bus_emit_signal_tov() were added in version 253.

See Also

sd-bus(3), busctl(1), sd_bus_message_new_signal(3), sd_bus_message_append(3), sd_bus_send(3), sd_bus_call_method(3)

Referenced By

sd-bus(3), sd_bus_add_object(3), sd_bus_add_object_manager(3), sd_bus_call_method(3), sd_bus_message_new_signal(3), systemd.directives(7), systemd.index(7).

The man pages sd_bus_emit_interfaces_added(3), sd_bus_emit_interfaces_added_strv(3), sd_bus_emit_interfaces_removed(3), sd_bus_emit_interfaces_removed_strv(3), sd_bus_emit_object_added(3), sd_bus_emit_object_removed(3), sd_bus_emit_properties_changed(3), sd_bus_emit_properties_changed_strv(3), sd_bus_emit_signal_to(3), sd_bus_emit_signal_tov(3) and sd_bus_emit_signalv(3) are aliases of sd_bus_emit_signal(3).

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