Setting up KVM Hypervisor on Ubuntu Groovy Gorilla (20.10)

Due to version LIBVIRT&&QEMU you are forced to deploy Ubuntu 20.10 on Btrfs file system . In particular case, Virtual Environment is a fair enough . See also Install KVM&Libvirt on SparkyLinux2020.08

Deployment L2 KVM Guest Manjaro XFCE 20.1.2 (Nested KVM enabled) inside Ubuntu 20.10

Otherwise, attempting to deploy L2 Guest you are supposed to get 

That is a reason

Setting up KVM

$ sudo apt -y install qemu-kvm \
    libvirt-daemon bridge-utils \
    virtinst libvirt-daemon-system
$ sudo apt -y install virt-top libguestfs-tools \
   libosinfo-bin  qemu-system virt-manager

$ sudo modprobe vhost_net 
$ lsmod | grep vhost
vhost_net              24576  0
tun                    49152  1 vhost_net
vhost                  49152  1 vhost_net
tap                    28672  1 vhost_net
$ echo vhost_net | sudo tee -a /etc/modules
$ sudo shutdown -r now 

Install Web Cockpit Console

 $  sudo apt install cockpit cockpit-machines
 $  sudo systemctl start cockpit.socket
 $  sudo systemctl enable cockpit.socket

 Tuning firewall
 $  sudo apt install firewalld
 $  sudo firewall-cmd --add-service=cockpit --permanent
 $  sudo firewall-cmd --reload

Per https://www.debugpoint.com/2020/08/fedora-33-release-info/

Fedora 33 workstation spins (KDE, GNOME, etc) will have the Btrfs file system as default rather than EXT4. Btrfs file system brings additional benefits over the EXT4 file system. Btrfs brings transparent file-system compression, SSD storage optimizations, native RAID support, better low disk space handling, and many more. All these advanced features are now part of the upcoming Fedora 33. To support Btrfs file-system lots of patches are being worked on the Fedora 33 kernel.

References

1. http://lxer.com/module/forums/t/36708/

2. https://www.debugpoint.com/2020/08/fedora-33-release-info/