NAME

       sd_bus_message_new_signal, sd_bus_message_new_signal_to - Create a signal message

SYNOPSIS

       #include <systemd/sd-bus.h>

       int sd_bus_message_new_signal(sd_bus *bus, sd_bus_message **m, const char *path, const char *interface,
                                     const char *member);

       int sd_bus_message_new_signal_to(sd_bus *bus, sd_bus_message **m, const char *destination,
                                        const char *path, const char *interface, const char *member);

DESCRIPTION

       The sd_bus_message_new_signal() function creates a new bus message object that encapsulates a D-Bus
       signal, and returns it in the m output parameter. The signal will be sent to path path, on the interface
       interface, member member. When this message is sent, no reply is expected. See
       sd_bus_message_new_method_call(1) for a short description of the meaning of the path, interface, and
       member parameters.

       sd_bus_message_new_signal_to() is a shorthand for creating a new bus message to a specific destination.
       It's behavior is similar to calling sd_bus_message_new_signal() followed by calling
       sd_bus_message_set_destination(3).

RETURN VALUE

       This function returns 0 if the message object was successfully created, and a negative errno-style error
       code otherwise.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           The output parameter m is NULL.

           The path parameter is not a valid D-Bus path ("/an/object/path"), the interface parameter is not a
           valid D-Bus interface name ("an.interface.name"), or the member parameter is not a valid D-Bus member
           ("Name").

       -ENOTCONN
           The bus parameter bus is NULL or the bus is not connected.

       -ENOMEM
           Memory allocation failed.

NOTES

       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.

EXAMPLES

       Example 1. Send a simple signal

           /* SPDX-License-Identifier: MIT-0 */

           #include <systemd/sd-bus.h>
           #define _cleanup_(f) __attribute__((cleanup(f)))

           int send_unit_files_changed(sd_bus *bus) {
             _cleanup_(sd_bus_message_unrefp) sd_bus_message *message = NULL;
             int r;

             r = sd_bus_message_new_signal(bus, &message,
                                           "/org/freedesktop/systemd1",
                                           "org.freedesktop.systemd1.Manager",
                                           "UnitFilesChanged");
             if (r < 0)
               return r;

             return sd_bus_send(bus, message, NULL);
           }

       This function in systemd sources is used to emit the "UnitFilesChanged" signal when the unit files have
       been changed.

SEE ALSO

       systemd(1), sd-bus(3), sd_bus_emit_signal(3) sd_bus_message_set_destination(3)

systemd 255                                                                         SD_BUS_MESSAGE_NEW_SIGNAL(3)