'\" t
.TH "SD_BUS_MESSAGE_NEW_SIGNAL" "3" "" "systemd 256.7" "sd_bus_message_new_signal"
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.nh
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
sd_bus_message_new_signal, sd_bus_message_new_signal_to \- Create a signal message
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'int\ sd_bus_message_new_signal('u
.BI "int sd_bus_message_new_signal(sd_bus\ *" "bus" ", sd_bus_message\ **" "m" ", const\ char\ *" "path" ", const\ char\ *" "interface" ", const\ char\ *" "member" ");"
.HP \w'int\ sd_bus_message_new_signal_to('u
.BI "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" ");"
.SH "DESCRIPTION"
.PP
The
\fBsd_bus_message_new_signal()\fR
function creates a new bus message object that encapsulates a D\-Bus signal, and returns it in the
\fIm\fR
output parameter\&. The signal will be sent to path
\fIpath\fR, on the interface
\fIinterface\fR, member
\fImember\fR\&. When this message is sent, no reply is expected\&. See
\fBsd_bus_message_new_method_call\fR(1)
for a short description of the meaning of the
\fIpath\fR,
\fIinterface\fR, and
\fImember\fR
parameters\&.
.PP
\fBsd_bus_message_new_signal_to()\fR
is a shorthand for creating a new bus message to a specific destination\&. It\*(Aqs behavior is similar to calling
\fBsd_bus_message_new_signal()\fR
followed by calling
\fBsd_bus_message_set_destination\fR(3)\&.
.SH "RETURN VALUE"
.PP
This function returns 0 if the message object was successfully created, and a negative errno\-style error code otherwise\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
The output parameter
\fIm\fR
is
\fBNULL\fR\&.
.sp
The
\fIpath\fR
parameter is not a valid D\-Bus path ("/an/object/path"), the
\fIinterface\fR
parameter is not a valid D\-Bus interface name ("an\&.interface\&.name"), or the
\fImember\fR
parameter is not a valid D\-Bus member ("Name")\&.
.RE
.PP
\fB\-ENOTCONN\fR
.RS 4
The bus parameter
\fIbus\fR
is
\fBNULL\fR
or the bus is not connected\&.
.RE
.PP
\fB\-ENOMEM\fR
.RS 4
Memory allocation failed\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "EXAMPLES"
.PP
\fBExample\ \&1.\ \&Send a simple signal\fR
.sp
.if n \{\
.RS 4
.\}
.nf
/* 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);
}
.fi
.if n \{\
.RE
.\}
.PP
This function in systemd sources is used to emit the
"UnitFilesChanged"
signal when the unit files have been changed\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_emit_signal\fR(3), \fBsd_bus_message_set_destination\fR(3)