sd_bus_message_new_signal(3) — Linux manual page


SD_BUS_M...EW_SIGNAL(3) sd_bus_message_new_signalSD_BUS_M...EW_SIGNAL(3)

NAME         top

       sd_bus_message_new_signal, sd_bus_message_new_signal_to - Create
       a signal message

SYNOPSIS         top

       #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         top

       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

RETURN VALUE         top

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

       Returned errors may indicate the following problems:

           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 (""), or the member
           parameter is not a valid D-Bus member ("Name").

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

           Memory allocation failed.

NOTES         top

       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

EXAMPLES         top

       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,
             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         top

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

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

systemd 255                                      SD_BUS_M...EW_SIGNAL(3)

Pages that refer to this page: sd-bus(3)sd_bus_emit_signal(3)sd_bus_message_get_type(3)sd_bus_message_new(3)systemd.directives(7)systemd.index(7)