[Ubuntu] system does not fully support snapd: cannot mount squashfs image using “squashfs”

My friend just have his server installed with Ubuntu 18.04 and somehow snap wouldn’t install packages. He tried to install docker

$ sudo snap install docker

$ sudo snap install docker

Then he got

error: system does not fully support snapd:
       cannot mount squashfs image using "squashfs": mount: /tmp/sanity-mountpoint-758431887: unknown filesystem type 'squashfs'.

The cause

I’m not an expert to explain about this. But for sure, it is the problem with kernel. You might be using an outdated kernel, or perhaps using some custom kernel shipped by your provider. To check, run

$ uname -r

My friend’s server kernel was 4.19-ovh-xxxx-std-ipv6-64. Turned out he was using a kernel provided by his provider, outdated too. You might too.

Solution

The solution is pretty straight forward. you need to install latest kernel available for your Ubuntu version.

Ubuntu 16.04

$ sudo apt install linux-image-generic-hwe-16.04 linux-headers-generic-hwe-16.04

Ubuntu 18.04

$ sudo apt install linux-image-generic-hwe-18.04 linux-headers-generic-hwe-18.04

Ubuntu 20.04

$ sudo apt install linux-image-generic-hwe-20.04 linux-headers-generic-hwe-20.04

Then a simple reboot should complete it

$ sudo reboot