Uqbar, what version of Ubuntu are you using, and what kernel version?
> I cannot see any possibility that "any non-Ubuntu container" (actually anything else) is started earlier than this. Isn't it?
Quite simply, the machine could be running any kind of supervisor (Xen, Hyper-V, ESX...), which could change the microcode of the CPU, and then much later boot Ubuntu in a VM. Most likely, Ubuntu detects such cases and there is no problem, but I believe this is what Alexander E. Patrakov had in mind when mentioning non-Ubuntu containers.
Uqbar, what version of Ubuntu are you using, and what kernel version?
> I cannot see any possibility that "any non-Ubuntu container" (actually anything else) is started earlier than this. Isn't it?
Quite simply, the machine could be running any kind of supervisor (Xen, Hyper-V, ESX...), which could change the microcode of the CPU, and then much later boot Ubuntu in a VM. Most likely, Ubuntu detects such cases and there is no problem, but I believe this is what Alexander E. Patrakov had in mind when mentioning non-Ubuntu containers.