This is an issue with newer kernels (containing this commit, which was backported into Ubuntu 5.4.0-80) and older k3s versions. Rancher only runs “in” a k8s cluster, so the docker container version runs a copy of k3s inside it to provide that cluster. That version needs to be updated in an upcoming release, or you need a kernel that doesn’t have that change, or install following the helm/HA installation instructions instead of docker run ....