How To Install Kernel 6.12.21 On Ubuntu, Debian And Derivative Systems

The Linux kernel is the core component of any Linux operating system, managing hardware resources and system processes.

The latest Kernel from the 6.12 series is Kernel 6.12.21, which has been recently released, coming with a few changes only:

MPTCP (MultiPath TCP): Addressed a bug that could cause data stream corruption during address announcements, enhancing the reliability of multipath connections.
Memory Management: Resolved an issue where large folios beyond the end-of-file (EOF) were not being properly released, preventing potential memory leaks.
ARM64 Architecture: Corrected the device tree source for the NanoPi R4S board by ensuring the USB PHY’s status aligns with the USB host controllers, preventing initialization errors for disabled USB ports.
libsubcmd Library: Silenced a compiler warning by initializing a pointer to NULL in the options__order function, leading to cleaner builds.

In this guide we will be installing Kernel 6.12.21, which has been released a while go, bringing some fixes and enhancements only.

Check your current kernel version:

Before proceeding with the installation, verify your current kernel version by running:

uname -r

How to install Kernel 6.12.21 on Ubuntu, Linux Mint, Debian, and derivative systems (amd64/x86_64):

Step 1: Update Your System

Run the following commands to ensure your system is up to date:

sudo apt update && sudo apt upgrade -y

This will update your package list and upgrade all installed packages to their latest versions.

What Does apt update Do?
This command updates the package list to reflect the latest versions available from your repositories.
What Does apt upgrade Do?
It upgrades all the packages that have new versions available while keeping existing dependencies intact.

Step 2: Download the Kernel 6.12.21 Packages

Download the necessary kernel packages from the official Ubuntu repositories or the kernel website:

wget -c https://kernel.ubuntu.com/mainline/v6.12.21/amd64/linux-headers-6.12.21-061221-generic_6.12.21-061221.202503282147_amd64.deb
wget -c https://kernel.ubuntu.com/mainline/v6.12.21/amd64/linux-headers-6.12.21-061221_6.12.21-061221.202503282147_all.deb
wget -c https://kernel.ubuntu.com/mainline/v6.12.21/amd64/linux-image-unsigned-6.12.21-061221-generic_6.12.21-061221.202503282147_amd64.deb
wget -c https://kernel.ubuntu.com/mainline/v6.12.21/amd64/linux-modules-6.12.21-061221-generic_6.12.21-061221.202503282147_amd64.deb

Step 3: Install the New Kernel

Install the downloaded packages using dpkg:

sudo dpkg -i linux-headers-6.12*.deb linux-modules-6.12*.deb linux-image-6.12*.deb

Step 4: Update GRUB and Reboot

Once the kernel installation is complete, update GRUB to ensure the new kernel is recognized:

Regenerate the GRUB Configuration

Run the following command to update GRUB with the latest installed kernel:

sudo update-grub

Verify GRUB Configuration

To confirm that the new kernel has been detected, check the GRUB configuration:

cat /boot/grub/grub.cfg | grep 'menuentry'

This should list all available kernels, including Kernel 6.12.21.

Reboot the System

Restart your computer to apply the changes:

sudo reboot

Select the New Kernel (if needed)If the system doesn’t automatically boot into the new kernel, you can manually select it:
- Hold Shift or Esc during boot to access the GRUB menu.
- Navigate to Advanced options for Ubuntu.
- Choose the entry with Kernel 6.12.19Kernel 6.12.21.
- Press Enter to boot.

Verifying the Installed Kernel

After rebooting, confirm the new kernel version:

uname -r

Rolling Back to a Previous Kernel

If you encounter issues with the new kernel, you can revert to an older version:

Reboot and Access the GRUB Menu -Restart your system and hold Shift or Esc to enter the GRUB boot menu.
Select Advanced options for Ubuntu – Choose an older kernel version and boot into it.
Remove Kernel 6.12.21 (if desired) – If you prefer to remove the new kernel permanently, run:

sudo apt remove linux-headers-6.12* linux-modules-6.12* linux-image-6.12*
sudo update-grub
sudo reboot

Conclusion

The Linux Kernel 6.12.21 release delivers important bug fixes and refinements, ensuring improved stability, efficiency, and reliability. Key updates include fixes for MPTCP, memory management, and ARM64 architecture, addressing issues that could cause data corruption, memory leaks, or hardware initialization failures. These improvements are crucial for maintaining a smooth and secure user experience across various Linux-based systems.

Beyond individual fixes, this update highlights the continuous effort to refine and optimize the kernel. The corrections in memory management and ARM64 device tree sources demonstrate the importance of maintaining system integrity, while the libsubcmd library fix helps streamline development and compilation processes. These refinements reinforce Linux’s commitment to high-quality, maintainable code.

With each patch release, the Linux kernel ecosystem grows stronger, providing a solid foundation for everything from servers and embedded systems to personal computing. Users are encouraged to update their systems to benefit from these latest improvements, ensuring they take advantage of the most recent stability, security, and performance enhancements.