1. Install the LTS kernel

sudo apt install linux-t2-lts

2. Make GRUB show the boot menu

By default GRUB skips the menu and boots directly. To see the kernel selection screen, edit the GRUB config:

sudo nano /etc/default/grub

Change these lines:

GRUB_TIMEOUT_STYLE=menu
GRUB_TIMEOUT=5

Apply and reboot:

❯ sudo update-grub
❯ sudo reboot

3. Select the LTS kernel

After the Apple boot manager (Option ⌥), the GRUB menu will appear. Select Advanced options for Ubuntu, then choose the LTS kernel (e.g. 6.18.25-1-t2-noble).

4. Verify

❯ uname -r
6.18.25-1-t2-noble

You should see something like 6.18.25-1-t2-noble.

5. Set the LTS kernel as default

Edit GRUB config again:

❯ sudo vim /etc/default/grub

Change the GRUB_DEFAULT line to:

GRUB_DEFAULT="Advanced options for Ubuntu>Ubuntu, with Linux 6.18.25-1-t2-noble"

Apply:

❯ sudo update-grub

Note: GRUB defaults to GRUB_DEFAULT=0, which picks the highest version number (e.g. 7.0.1). Since the LTS kernel has a lower version number (6.18.x), you must set it explicitly.

6. Clean up old kernel leftovers

To purge leftover configs from previously removed kernels (marked rc):

sudo dpkg --purge $(dpkg --list | grep '^rc' | grep linux-image | awk '{print $2}')
sudo update-grub

7. (Optional) Remove the old mainline kernel

Only after confirming the LTS kernel works properly:

sudo apt remove linux-headers-7.0.1-1-t2-noble linux-image-7.0.1-1-t2-noble
sudo update-grub

Warning: Don’t remove the old kernel before rebooting and verifying the LTS one works. If something goes wrong, you still have the mainline kernel to fall back to via GRUB.