Ubuntu Touch, also known as the Ubuntu Phone, is the Ubuntu flavor specifically designed for touch devices such as smartphones and tablets. Although it's based on the same core packages as its desktop counterpart, it follows a completely different release and upgrade model. One of the reasons for that is because the touch devices use an image-based update mechanism on top of its default read-only core filesystem.

This means that a phone user only gets new and upgraded core packages for its system when an image is built and published to the respective stable image channel – notifying the users of the available over-the-air (OTA) upgrade. However, this happens only after each change goes through various stages of development, quality assurance, testing, and coordination.

In this article, I'll take a look at how all this works. An overview of the general release workflow can be seen in Figure 1. I'll start this update journey from the very top – the code.

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