---
name: "sd_bus_message_get_cookie"
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_get_cookie"
---

# sd\_bus\_message\_get\_cookie(3)

Return the transaction cookie of a message

## NAME

sd\_bus\_message\_get\_cookie, sd\_bus\_message\_get\_reply\_cookie - Return the transaction cookie of a message

## SYNOPSIS

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

**int sd\_bus\_message\_get\_cookie(sd\_bus\_message \****message***, uint64\_t \****cookie***);**

**int sd\_bus\_message\_get\_reply\_cookie(sd\_bus\_message \****message***, uint64\_t \****cookie***);**

## DESCRIPTION

**sd\_bus\_message\_get\_cookie()** returns the transaction cookie of a message. The cookie uniquely identifies a message within each bus peer, but is not globally unique. It is assigned when a message is sent.

**sd\_bus\_message\_get\_reply\_cookie()** returns the transaction cookie of the message the specified message is a response to. When a reply message is generated for a method call message, its cookie is copied over into this field. Note that while every message that is transferred is identified by a cookie, only response messages carry a reply cookie field.

Both functions take a message object as first parameter and a place to store the 64-bit cookie in.

## RETURN VALUE

On success, these calls return 0 or a positive integer. On failure, they return a negative errno-style error code.

On success, the cookie/reply cookie is returned in the specified 64-bit unsigned integer variable.

### Errors

Returned errors may indicate the following problems:

**-EINVAL**

A specified parameter is invalid.

**-ENODATA**

No cookie has been assigned to this message. This either indicates that the message has not been sent yet and hence has no cookie assigned, or that the message is not a method response message and hence does not carry a reply cookie field.

## 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\_get\_cookie()** and **sd\_bus\_message\_get\_reply\_cookie()** were added in version 209.

## SEE ALSO

[**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_new**(3)](/sd_bus_new/3.md)