---
name: "sd_bus_message_new"
section: "3"
platform: "linux"
package: "systemd-libs"
version: "262.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/sd_bus_message_new"
---

# sd\_bus\_message\_new(3)

Create a new bus message object and create or destroy references to it

## NAME

sd\_bus\_message\_new, sd\_bus\_message\_ref, sd\_bus\_message\_unref, sd\_bus\_message\_unrefp, SD\_BUS\_MESSAGE\_METHOD\_CALL, SD\_BUS\_MESSAGE\_METHOD\_RETURN, SD\_BUS\_MESSAGE\_METHOD\_ERROR, SD\_BUS\_MESSAGE\_SIGNAL, sd\_bus\_message\_get\_bus - Create a new bus message object and create or destroy references to it

## SYNOPSIS

```
#include <systemd/sd-bus.h>
```

```
enum {
      SD_BUS_MESSAGE_METHOD_CALL,
      SD_BUS_MESSAGE_METHOD_RETURN,
      SD_BUS_MESSAGE_METHOD_ERROR,
      SD_BUS_MESSAGE_SIGNAL,
};
```

**int sd\_bus\_message\_new(sd\_bus \****bus***, sd\_bus\_message \*\****m***, uint8\_t** *type***);**

**sd\_bus\_message \*sd\_bus\_message\_ref(sd\_bus\_message \****m***);**

**sd\_bus\_message \*sd\_bus\_message\_unref(sd\_bus\_message \****m***);**

**void sd\_bus\_message\_unrefp(sd\_bus\_message \*\****mp***);**

**sd\_bus \*sd\_bus\_message\_get\_bus(sd\_bus\_message \****m***);**

## DESCRIPTION

**sd\_bus\_message\_new()** creates a new bus message object attached to the bus *bus* and returns it in the output parameter *m*. This object is reference-counted, and will be destroyed when all references are gone. Initially, the caller of this function owns the sole reference to the message object. Note that the message object holds a reference to the bus object, so the bus object will not be destroyed as long as the message exists.

Note: this is a low-level call. In most cases functions like [**sd\_bus\_message\_new\_method\_call**(3)](/sd_bus_message_new_method_call/3.md), [**sd\_bus\_message\_new\_method\_error**(3)](/sd_bus_message_new_method_error/3.md), [**sd\_bus\_message\_new\_method\_return**(3)](/sd_bus_message_new_method_return/3.md), and [**sd\_bus\_message\_new\_signal**(3)](/sd_bus_message_new_signal/3.md) that create a message of a certain type and initialize various fields are easier to use.

The *type* parameter specifies the type of the message. It must be one of **SD\_BUS\_MESSAGE\_METHOD\_CALL** — a method call, **SD\_BUS\_MESSAGE\_METHOD\_RETURN** — a method call reply, **SD\_BUS\_MESSAGE\_METHOD\_ERROR** — an error reply to a method call, **SD\_BUS\_MESSAGE\_SIGNAL** — a broadcast message with no reply.

The flag to allow interactive authorization is initialized based on the current value set in the bus object, see [**sd\_bus\_set\_allow\_interactive\_authorization**(3)](/sd_bus_set_allow_interactive_authorization/3.md). This may be changed using [**sd\_bus\_message\_set\_allow\_interactive\_authorization**(3)](/sd_bus_message_set_allow_interactive_authorization/3.md).

**sd\_bus\_message\_ref()** increases the internal reference counter of *m* by one.

**sd\_bus\_message\_unref()** decreases the internal reference counter of *m* by one. Once the reference count has dropped to zero, message object is destroyed and cannot be used anymore, so further calls to **sd\_bus\_message\_ref()** or **sd\_bus\_message\_unref()** are illegal.

**sd\_bus\_message\_unrefp()** is similar to **sd\_bus\_message\_unref()** but takes a pointer to a pointer to an **sd\_bus\_message** object. This call is useful in conjunction with GCC's and LLVM's **Clean-up Variable Attribute**\[1\]. See [**sd\_bus\_new**(3)](/sd_bus_new/3.md) for an example how to use the cleanup attribute.

**sd\_bus\_message\_ref()** and **sd\_bus\_message\_unref()** execute no operation if the passed in bus message object address is **NULL**. **sd\_bus\_message\_unrefp()** will first dereference its argument, which must not be **NULL**, and will execute no operation if *that* is **NULL**.

**sd\_bus\_message\_get\_bus()** returns the bus object that message *m* is attached to.

## RETURN VALUE

On success, **sd\_bus\_message\_new()** returns 0 or a positive integer. On failure, it returns a negative errno-style error code.

**sd\_bus\_message\_ref()** always returns the argument.

**sd\_bus\_message\_unref()** always returns **NULL**.

**sd\_bus\_message\_get\_bus()** always returns the bus object.

### Errors

Returned errors may indicate the following problems:

**-EINVAL**

Specified *type* is invalid.

**-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.

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)](/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.

## HISTORY

**sd\_bus\_message\_new()**, **sd\_bus\_message\_ref()**, **sd\_bus\_message\_unref()**, **sd\_bus\_message\_unrefp()**, and **sd\_bus\_message\_get\_bus()** were added in version 240.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_new**(3)](/sd_bus_new/3.md), [**sd\_bus\_message\_new\_method\_call**(3)](/sd_bus_message_new_method_call/3.md), [**sd\_bus\_message\_new\_method\_error**(3)](/sd_bus_message_new_method_error/3.md), [**sd\_bus\_message\_new\_method\_return**(3)](/sd_bus_message_new_method_return/3.md), [**sd\_bus\_message\_new\_signal**(3)](/sd_bus_message_new_signal/3.md)

## NOTES

- 1\.

  Clean-up Variable Attribute

  https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html