Android, like many other operating systems, relies on the open-source Linux kernel. The Long-Term Support (LTS) versions of Linux are crucial for Android, as they receive regular bug fixes and security patches. In 2017, the Linux community extended LTS support from two years to six years, but this was reversed in early 2023. Google has now committed to supporting its own LTS kernel releases for four years, which is vital for the security and functionality of Android devices.
The Linux kernel used in Android devices typically comes from Google's Android Common Kernel (ACK) branches, created from the Android mainline kernel whenever a new LTS version is declared. For instance, the `android15-6.6` ACK branch was formed after version 6.6 was announced as the latest LTS release, aligning with Android 15. Google maintains its own forks of each LTS release to:
- Integrate necessary upstream functionality for Android features.
- Ship features that are still under development upstream but ready for Android devices.
- Include vendor-specific features beneficial for Android partners.
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| For Android 15 and beyond, devices must launch with either `android14-6.1` or `android15-6.6` |
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| ACK branches |
ACK branches receive continuous updates from Google, incorporating Android-specific bug fixes and merges from upstream kernel branches. These updates address vulnerabilities disclosed in the monthly Android Security Bulletin, like those listed in the July 2024 bulletin. Identifying security fixes can be challenging because a bug fix might inadvertently close a security hole that is not immediately apparent.
With the Linux kernel LTS lifecycle reverting to two years, there's more pressure on Android OEMs to keep their devices secure. Without regular LTS updates, devices could become vulnerable. Google’s strategy to support its LTS kernels for four years helps mitigate this risk. For Android 15 and beyond, devices must launch with either `android14-6.1` or `android15-6.6`, ensuring three to five years of support from the launch date before needing a kernel upgrade.
Google plans to introduce only one new ACK branch per kernel release, simplifying the process for OEMs. Devices launching with Android 15 must use the latest kernel versions, forcing OEMs to consider major kernel upgrades to support longer update policies.
Google’s commitment to maintaining its LTS kernel releases for four years highlights the importance of keeping Android devices secure and up-to-date. This approach addresses the challenges posed by shorter upstream LTS support and sets a clear path for OEMs to support their devices. As Android evolves, these measures will help ensure that devices remain secure and functional throughout their lifecycle.