Run your own kernel with WSL2

In case you need a specific kernel feature that the vanilla kernel shipped from Microsoft for WSL2 does not include then you can build a custom one and instruct WSL2 to load it instead of loading the default one. This is simpler then it sounds, so I have gathered the steps below as a future cookie for me and others. Take a note of the expiration date though. Cookies do tend to expire…

As an example, I will add Open-vswitch support at the kernel since I wanted that for some networking tests. You can go and configure anything you need.

1. Inside WSL2 console, fetch the kernel code. Here we fetch the same Microsoft published Linux kernel though you could grab one from kernel.org if you feel so.

git clone https://github.com/microsoft/WSL2-Linux-Kernel.git — depth=1 -b linux-msft-wsl-6.1.y

2. Install the required packages so as to be able to build the kernel:

sudo apt update && sudo apt install build-essential flex bison libssl-dev libelf-dev libncurses5-dev

3. Configure the Microsoft WSL2 kernel:

make menuconfig KCONFIG_CONFIG=Microsoft/config-wsl

4. Enable the kernel feature you need. In my case it will be: Networking support -> Open vSwitch

5. Compile the kernel:

make -j$(nproc) KCONFIG_CONFIG=Microsoft/config-wsl

6. Install the kernel modules and headers:

make modules_install headers_install

7. Create a directory and copy your custom kernel there. Replace USER with your username:

mkdir -p /mnt/c/Users/USER/.wsl-kernels/
cp arch/x86/boot/bzImage /mnt/c/Users/USER/.wsl-kernels/

8. Configure WSL2 to point to this new kernel. Create or edit the file /mnt/c/Users/USER/.wslconfig with the following content:

[wsl2] 
kernel=C:\\Users\\USER\\.wsl-kernels\\bzImage

9. Shutdown and start WSL:

wsl --shutdown
wsl

10. Verify kernel version:

uname -r