6

I've noticed that when the live kernel update is enabled through Ubuntu Pro, the kernel gets updated, but doesn't get activated until you reboot so I'm wondering what is the point if you have to reboot to activate the kernel anyway?

muru
  • 207,970
Jaime
  • 420
  • I don't currently use it on Ubuntu, but consider checking out kexec. It might be useful for you depending on your goal. – cocomac Dec 01 '24 at 03:09

1 Answers1

8

When using the live kernel patching feature of Ubuntu Pro, updates to the kernel are applied dynamically while the system is running without requiring a reboot. One of the main benefits of live kernel patching is that security updates to the kernel can be applied immediately, maintaining uptime.

There are the following exceptions to live kernel patching.

  • If the kernel update includes new features or requires a major upgrade those changes will not take effect until a reboot. For example in Linux kernel 6.8.0-49 the major version is 6 and the minor version is 8. Upgrading the kernel from either of these major/minor versions to another version can require a reboot because these updates typically include changes that cannot be patched live.

  • If the changes being applied cannot be patched live for any other reason Ubuntu may still prompt the user for a reboot.

  • Live kernel patching primarily focuses on applying security updates to the running kernel, rather than full kernel version upgrades.

karel
  • 122,695
  • 134
  • 305
  • 337
  • 1
    Thank you. For futher explanation, I never get the "Reboot required" prompt. However, once the update is complete, if I enter the "uname -r" command, it still shows the old kernel in effect. The new kernel doesn't get displayed until after I reboot. – Jaime Dec 01 '24 at 17:36
  • 3
    Live kernel patches are applied without altering the core version. These are small, targeted fixes to the kernel currently running. No reboot is required because no full replacement of the entire kernel occurs. When the entire kernel is replaced, the update cannot be live because the whole kernel structure is replaced. A reboot is needed for the new kernel to take over. That's why the new kernel version doesn't get displayed until after rebooting. – karel Dec 01 '24 at 22:11
  • 1
    I also notice the same thing as I new to ubuntu. With Debian, I am notified that a reboot is required and I have set a time when it is safe to reboot the system. Ubuntu just updated the kernel with unattended upgrades with no reboot required. The new kernel is not in use without a reboot so I don't get it. – Deihmos May 03 '25 at 02:53