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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.
All functions listed here are thread-agnostic and only a single
thread may operate on a given object at any given time. Different
threads may access the same object at different times. Multiple
independent objects may be used from different threads in
parallel.
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 2026-08-04. (At that
time, the date of the most recent commit that was found in the
repository was 2026-08-03.) 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
man-pages@man7.org
systemd 262~devel 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 2026-09-09 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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