Debug/step into a Linux boot

Question

Is there a way to watch Linux boot as though it was a program compiled with GCC on a Linux environment using the -g switch so, say, I can step through the entire boot sequence from GRUB onwards, choosing to step through at C source level or assembly when necessary/desirable, by using GDB or a GDB-like tool?

I suspect it would require a virtual machine at least, to watch the boot on a host environment. Any elaboration on this topic of observing a boot would be appreciated!

Answer 1

bootchart contains an init(8) replacement that logs how long (and how much disk IO) processes take at boot time. While getting a single-step style boot out of init(8) (whether it is upstart, systemd, or the old-and-trusty SysV-style init) might be very difficult, at least you can take a look after the fact of what happens when.