After using microk8s for a while, there may be increased disk usage due to a number of docker images saved in /var dir. You can delete these images using crictl tool. It is not part of microk8s installation, so you need to download first.
Install crictl #
Download crictl
Connect to containerd #
sudo ./crictl -r unix:///var/snap/microk8s/common/run/containerd.sock image lis/
Delete unused images #
sudo ./crictl -r unix:///var/snap/microk8s/common/run/containerd.sock rmi --prune