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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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SD_BUS_M...EW_SIGNAL(3) sd_bus_message_new_signal SD_BUS_M...EW_SIGNAL(3)
sd_bus_message_new_signal, sd_bus_message_new_signal_to - Create a
signal message
#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);
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(3) 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).
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.
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.
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.
systemd(1), sd-bus(3), sd_bus_emit_signal(3),
sd_bus_message_set_destination(3)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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
[email protected]
systemd 258~rc2 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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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