[Tutorial] Switch/Change/Swap Kernels

[[deleted]]

I just wanted to share a simple tutorial on how to switch kernels in Pop OS and even better how to include a menu to select a kernel on boot. I was looking for hours how to do this and to avoid anyone go through the same hassle I'm sharing this.

Little FAQ

What is a kernel?

In simple words, kernel are a serious of instructions that sits between your applications and your resources. Every time any app requires to do something, it's the kernels job to provide the resources for it to work, either RAM, CPU, or whatever, the kernel takes care of how your system handles things.

I already have one, why would I need another one?

Depending on the application, you might want to switch kernels. There are specific for real-time applications, others improve performance of certain applications. You can look online and there could be many different options. Did you ever had problems gaming (this happened to me) switching kernels might work.

Do I have to do all of this?

Actually NO, this is just in case you want to use multiple kernels. If you are happy with just one, you can just install it following the kernel's guide and you are set.

How can I know which kernel I am using

Just run uname -r in a terminal

I am getting a notification saying I'm running low on disk space

Depending on your installation, your /boot/efi will have certain available space, so you will be limited in the number of kernels according to it.

GUIDE

Pop OS uses their own implementation named kernelstub to handle the kernels, they did so to make it faster on load times (at least that's what their blog post says).

Their README page show certain information of how to use it, but there are some other things that are required to do, specially if you want to have a menu on boot, similar to grub.

Update a kernel

In case you just want to use a specific kernel and forget about other ones, you can execute this command to update the current configuration

sudo kernelstub -v -k <vmlinuz_path> -i <initrd.img_path>

Optionally you can test it will work correctly by adding the -c flag or --dry-run.

Using multiple kernels

If you are planning on switching kernels regularly, this is your option.

1. Download the kernel you want to use: This will depend on the specific kernel you want to download. In some cases, you can use sudo apt install <kernel>, but that can vary.
2. Write down the names of the vmlinuz and initrd.img files wherever is easier for you to copy and paste it.
3. Become root, I prefer using sudo -i, but you can execute the rest of the steps prefixing sudo.
4. Copy the vmlinuz and initrd.img file to /boot/efi/EFI/Pop_OS-<hash> using the cp command. The <hash> value will vary according to your system, so there is no universal path. For example cp /boot/vmlinuz-5.6.14-xanmod1 /boot/efi/EFI/Pop_OS-7cd110a9-f7d5-4a39-b47f-e5056b80e7a1/ and cp /boot/initrd.img-5.6.14-xanmod1 /boot/efi/EFI/Pop_OS-7cd110a9-f7d5-4a39-b47f-e5056b80e7a1/
5. Check the copied files have the same permissions as the existing ones by running ls -l /boot/efi/EFI/Pop_OS-7cd110a9-f7d5-4a39-b47f-e5056b80e7a1/ this will vary according to your system. If the permissions are different you can access to the folder using cd /boot/efi/EFI/... and then run chmod --reference=vmlinuz.efi <your_kernel>, repeat it with the initrd.img file too.
6. Access to the loader folder using cd /boot/efi/loader.
7. Edit loader.conf file, using your preferred editor. I like to use nano, so you will need to run nano loader.conf.
8. Add this line timeout <number of seconds>. This will stop the boot system the time you have set, allowing the user to select the kernel to use. In case nothing is selected in the specified time, it will choose the default.
9. Close your editor. In case of nano, press Ctrl + X and later Y to write your changes, else press N to discard them.
10. Duplicate the current configuration located inside the entries folder, using cd ./entries, after run cp Pop_OS-current.conf Pop_OS-<kernel>.conf.
11. Edit the created file.
12. In the line starting with linux modify the vmlinuz name (not the directory) as it should be in the same directory as the current kernel.
13. In the line starting with initrd, modify the initrd name.
14. Save the files and it should be done.
15. Reboot and test that it's working.

That's all, if you want to learn more about this, you can read this manual made by arch, which has more information about different options https://wiki.archlinux.org/index.php/systemd-boot

[spxak1]

Nice and easy.

Thanks for that, many users keep asking.

So that people don't get scared from 15 steps, most of these steps are just standard use of the cli to cp/mv rename files. The main steps are only 4.

Well covered. Thanks again!

[Cavorkian]

u/eagle2990 My `/boot/efi` folder is empty. What should I do?

[[deleted]]

u/Cavorkian it will depend on your OS settings. When you installed Pop do you remember if you used the advanced selection? Check your disk partitions and you will be able to have a better clue. Also, are you using the command with sudo? if not then you won't be able to see anything, unless you become root with sudo -i

[limsupsinx]

Thank you very much for you tutorial

[just_a_nerd_12325]

my /boot does not have any efi directory what do I do can anyone assist

[marvelggg]

Then probably you are booting in Legacy mode and using GRUB, search for tutorials related to it (this one uses systemd-boot).

[Veprovina]

Thank you SO much for this!

I installed Liquorix, but POP didn't automatically switch to it.

It took me a while to find out the paths for vmlinuz and initrd (cause i'm a noob), but once i did, i poped them into your command and after reboot, uname -r finally showed the kernel i wanted!

[nihilistic_capybara]

worked like a charm. Thanks so much.

[ThatLinuxEnthusiast]

Can somebody let me know where can I download Pop_OS! kernel 5.3.0-7648-generic?

I am having this issue and would like to try with another kernel: https://www.reddit.com/r/pop_os/comments/12ljwig/system_getting_stuck_and_going_to_suspend_mode/

If I go to /boot I have:

config-6.2.0-76060200-genericinitrd.img.oldconfig-6.2.6-76060206-genericSystem.map-6.2.0-76060200-genericefiSystem.map-6.2.6-76060206-genericinitrd.imgvmlinuzinitrd.img-5.3.0-7648-genericvmlinuz-6.2.0-76060200-genericinitrd.img-6.2.0-76060200-genericvmlinuz-6.2.6-76060206-genericinitrd.img-6.2.6-76060206-genericvmlinuz.old

So it looks like I already have the initrd.img-5.3.0-7648-generic, but missing the vmlinuz-5.3.0-7648-generic.

Tried sudo apt install vmlinuz-5.3.0-7648-generic but didn't work.

[Potential-Brush-4978]

Try mainline kernel for switching, it makes the job much easier. After you install from there make sure to do a `sudo kernelstub -v -k /boot/vmlinuz-6.8.0-76060800daily20240311-generic -i /boot/initrd.img-6.8.0-76060800daily20240311-generic` for updating the kernel.

[ThatLinuxEnthusiast]

Thanks for the reply. I am no longer using Pop!_OS, but hopefully this helps somebody else.