Why my ubuntu image from Docker Hub ships with 4.19 Linux Kernel?

Question

I'm using the Ubuntu 20.04 LTS image for various docker containers and recently realized, that they are running with the 4.19 linux kernel. I'm a bit curious why they are not running with the linux kernel 5.4 like mentioned in the release notes. Anyone has an idea what went wrong?

Procedure to reproduce:

• docker pull ubuntu:latest
• docker run ubuntu:latest bash
• uname -r
• cat /proc/version
• cat /etc/os-release

Results:

uname -r 
4.19.76-linuxkit

cat /proc/version
Linux version 4.19.76-linuxkit (root@4abe09437d05) (gcc version 8.3.0 (Alpine 8.3.0)) #1 SMP Tue May 26 11:42:35 UTC 2020

cat /etc/os-release
NAME="Ubuntu"
VERSION="20.04.1 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.1 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal

Answer 1

Nothing is wrong. Docker containers use the host kernel - they don't have their own.

Now, in your case, the fact it says 4.19.76-linuxkit suggests that you're running on Windows or macos. They obviously don't have an underlying Linux kernel, so docker actually runs in a VM with a lightweight Linux OS (linuxkit). That's the kernel version you see.