On Fedora 32 box (5.8.18-200.fc32.x86_64) I initially ran `virt-host-validate` and received the following output: ``` [baus@thundertwinkie ~]$ which virt-host-validate /usr/bin/virt-host-validate [baus@thundertwinkie ~]$ virt-host-validate QEMU: Checking for hardware virtualization : PASS QEMU: Checking if device /dev/kvm exists : PASS QEMU: Checking if device /dev/kvm is accessible : PASS QEMU: Checking if device /dev/vhost-net exists : PASS QEMU: Checking if device /dev/net/tun exists : PASS QEMU: Checking for cgroup 'cpu' controller support : PASS QEMU: Checking for cgroup 'cpuacct' controller support : PASS QEMU: Checking for cgroup 'cpuset' controller support : PASS QEMU: Checking for cgroup 'memory' controller support : PASS QEMU: Checking for cgroup 'devices' controller support : PASS QEMU: Checking for cgroup 'blkio' controller support : PASS QEMU: Checking for device assignment IOMMU support : PASS QEMU: Checking if IOMMU is enabled by kernel : WARN (IOMMU appears to be disabled in kernel. Add intel_iommu=on to kernel cmdline arguments) LXC: Checking for Linux >= 2.6.26 : PASS LXC: Checking for namespace ipc : PASS LXC: Checking for namespace mnt : PASS LXC: Checking for namespace pid : PASS LXC: Checking for namespace uts : PASS LXC: Checking for namespace net : PASS LXC: Checking for namespace user : PASS LXC: Checking for cgroup 'cpu' controller support : PASS LXC: Checking for cgroup 'cpuacct' controller support : PASS LXC: Checking for cgroup 'cpuset' controller support : PASS LXC: Checking for cgroup 'memory' controller support : PASS LXC: Checking for cgroup 'devices' controller support : PASS LXC: Checking for cgroup 'freezer' controller support : PASS LXC: Checking for cgroup 'blkio' controller support : PASS LXC: Checking if device /sys/fs/fuse/connections exists : PASS ``` After enabling IOMMU in grub, the output changed to the following: ``` [baus@thundertwinkie ~]$ virt-host-validate QEMU: Checking for hardware virtualization : PASS QEMU: Checking if device /dev/kvm exists : PASS QEMU: Checking if device /dev/kvm is accessible : PASS QEMU: Checking if device /dev/vhost-net exists : PASS QEMU: Checking if device /dev/net/tun exists : PASS QEMU: Checking for cgroup 'cpu' controller support : WARN (Enable 'cpu' in kernel Kconfig file or mount/enable cgroup controller in your system) QEMU: Checking for cgroup 'cpuacct' controller support : PASS QEMU: Checking for cgroup 'cpuset' controller support : WARN (Enable 'cpuset' in kernel Kconfig file or mount/enable cgroup controller in your system) QEMU: Checking for cgroup 'memory' controller support : PASS QEMU: Checking for cgroup 'devices' controller support : WARN (Enable 'devices' in kernel Kconfig file or mount/enable cgroup controller in your system) QEMU: Checking for cgroup 'blkio' controller support : WARN (Enable 'blkio' in kernel Kconfig file or mount/enable cgroup controller in your system) QEMU: Checking for device assignment IOMMU support : PASS QEMU: Checking if IOMMU is enabled by kernel : PASS LXC: Checking for Linux >= 2.6.26 : PASS LXC: Checking for namespace ipc : PASS LXC: Checking for namespace mnt : PASS LXC: Checking for namespace pid : PASS LXC: Checking for namespace uts : PASS LXC: Checking for namespace net : PASS LXC: Checking for namespace user : PASS LXC: Checking for cgroup 'cpu' controller support : FAIL (Enable 'cpu' in kernel Kconfig file or mount/enable cgroup controller in your system) LXC: Checking for cgroup 'cpuacct' controller support : PASS LXC: Checking for cgroup 'cpuset' controller support : FAIL (Enable 'cpuset' in kernel Kconfig file or mount/enable cgroup controller in your system) LXC: Checking for cgroup 'memory' controller support : PASS LXC: Checking for cgroup 'devices' controller support : FAIL (Enable 'devices' in kernel Kconfig file or mount/enable cgroup controller in your system) LXC: Checking for cgroup 'freezer' controller support : FAIL (Enable 'freezer' in kernel Kconfig file or mount/enable cgroup controller in your system) LXC: Checking for cgroup 'blkio' controller support : FAIL (Enable 'blkio' in kernel Kconfig file or mount/enable cgroup controller in your system) LXC: Checking if device /sys/fs/fuse/connections exists : PASS ``` cgroupsv2 appears to be enabled: ``` [root@thundertwinkie ~]# cat /sys/fs/cgroup/cgroup.controllers cpuset cpu io memory hugetlb pids ``` I believe when cgroupsv2 is enabled, the command should not be reporting v1 controller warnings/errors.