The Flattened Image Tree "FIT" 1.0 specification was recently finalized for this container format used by U-Boot on embedded systems for providing various boot components like DTBs, the Linux kernel image, and more into a single file.

The Flat(tened) Image Tree usage can lead to a simpler Linux boot experience for embedded platforms and making it easier to manage deploying of updates with the single container file for providing all of the needed boot assets plus allowing for verified boot functionality and related features. U-Boot spearheaded FIT years ago and since 2024 [1]the mainline Linux kernel has easily allowed buildint ARM64 Flat Image Trees .

While the Flat(tened) Image Tree has been around for nearly twenty years in the U-Boot space, only recently was there the v1.0 tag of the specification. As of yesterday is the [2]v1.0 tag as the " first official release of the FIT specification. "

Meanwhile [3]this commit last week bumped the specification to version 1.0 and tagged its date as 11 April. With this FIT v1.0 specification new additions include security architecture and hash contents documentation, DM-VERITY support for verifying file-system images, shared image data via the image-data property, multi-step loading support, and the configuration command line property. These features were added for FIT v0.9, which hadn't been tagged on GitHub until yesterday. The Flattened Image Tree v0.8 releases and prior were while it lived within the U-Boot space.

The commit bumping the FIT specification to v1.0 notes that there are still some " more major changes in the works " to this important specification for embedded Linux systems.



[1] https://www.phoronix.com/news/Linux-610-ARM64-Flat-Image-Tree

[2] https://github.com/open-source-firmware/flat-image-tree/releases/tag/v1.0

[3] https://github.com/open-source-firmware/flat-image-tree/commit/c210313ebfe360ca7d5855e7fb5684decf340438