The question is based on the false assumption that you can have two identical systems. That is not possible in this universe. For example, at a minimum, they would have to be in different places. Those different places will have different microscopic zone temperature variations. And those variations affect the phase relationship between the quartz oscillators that drive the CPU clock and the network clock.
Similarly, the microscopic surface defects in the disk platters and the inside of the hard drive case affect the turbulent shear of the air. This affects the rotation speed of the platters. There is no possible way you could have two hard drives with identical turbulent shear properties.
Even using the same clocks and the same hard drive, they'll still each issue their own requests. They'll still each receive their own network packets. They'll still each run their own separate path.
You would have to imagine a universe very different from ours for the question to even be asked. And yes, the Linux RNG algorithm does use these kinds of things.