---
name: "sd_bus_message_new_signal_to"
section: "3"
platform: "linux"
package: "libsystemd-dev"
version: "257.13-1~deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/sd_bus_message_new_signal"
---

# sd\_bus\_message\_new\_signal\_to(3)

Create a signal message

Part of [sd\_bus\_message\_new\_signal(3)](/sd_bus_message_new_signal/3.md).

## 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**(3)](/sd_bus_message_new_method_call/3.md) 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)](/sd_bus_message_set_destination/3.md).

## 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)](/pkg-config/1.md) file.

The code described here uses [**getenv**(3)](/getenv/3.md), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call [**setenv**(3)](/setenv/3.md) 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)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_emit\_signal**(3)](/sd_bus_emit_signal/3.md), [**sd\_bus\_message\_set\_destination**(3)](/sd_bus_message_set_destination/3.md)