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)