OS fundamentals drill

After a routine kernel upgrade, 3 of 200 identical-looking Linux servers do not come back. The serial console on each shows the kernel banner, then: Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0). Place the failure in the boot sequence, explain why only three servers failed, and recover them without reinstalling.

You are choosing the operating systems for a surgical robot. It has a motion-control loop that must run every 1 ms without exception, a camera and vision pipeline on a GPU, and a touchscreen UI for the surgeon. Decide which kernel architecture and OS family each part runs on, say where the device drivers live in each, and explain what a driver crash does to the system.

A C++ pricing service crashes about once a day with signal 11 and a core dump. A colleague proposes moving its hot path into a kernel module, arguing it would also remove the 300,000 system calls per second the service makes. Explain, in terms of CPU protection, what produced the crash and how you would locate the bug from the dump, then evaluate the kernel-module proposal.