Opennebula5.2上面启动ubuntu虚拟机时报如下错误

error: 无效参数:could not find capabilities for arch=x86_64 domaintype=kvm

In witch scenario you get that error? Probably you must enable nested virtualisation for the machine for KVM hypervisor. If you have enabled nested virtualisation than you can check that in linux cli with command: #lsmod | grep kvm
and output will be something like this:
kvm_intel 170200 0
kvm 566604 1 kvm_intel
irqbypass 13503 1 kvm

If it does not show anything then it means it does not support this vm virtualization.

To enable nested virtualisation you must next to do:
Again, to see if it supports nested virtualization with command:
#cat / sys / module / kvm_intel / parameters / nested
N

If the answer is N then it must be enabled in the following way:
edit the the file kvm-nested.conf
#vi /etc/modprobe.d/kvm-nested.conf
options kvm-intel nested=1
options kvm-intel enable_shadow_vmcs=1
options kvm-intel enable_apicv=1
options kvm-intel ept=1

and finally to execute commands:
#modprobe -r kvm_intel
#modprobe -a kvm_intel

Of course CPU must support virtualization, for Intel is VT-x technology.