is booting an OS without power cycling a host possible?

[Peter Van Wieren]

I have a host with linux distribution "A".  The host is presently running "A", 
and has already been started by grub.  There exists, on a second hard disk 
drive, linux distribution "B" is installed but not mounted.

I hoped I could transition from "A" to "B", without power cycling the host or 
editing the MBR, by running grub from the command line as root.  In a root 
shell I started grub and planned to issue the commands:

  1) root (hd1,0)
  2) kernel .... vmlinuz
  3) initrd ....
  4) boot

My hope was that distribution "B" would boot, and "A" would somehow be 
abolished.  I do not know for sure if the above is supposed to even be possible 
or not.  Can it be done?

I made it to step #3.  The trouble is the "initrd" command returns "Error 16: 
inconsistent filesystem"



P.S. Why would I want to do this?  Answer: I threw my old USB keyboard in the 
trash, and replaced it with a new one.  It was all well and good, until I found 
that the new keyboard doesn't work at all during the BIOS or GRUB stages -- the 
new keyboard only works after the OS has been booted.  Thus if I change the 
default option in grub.conf to "B" and something doesn't work, my host will 
become completely useless until such a time as I can locate a 2002 era USB 
keyboard -- which in theory should work in the BIOS and GRUB stages.

Thanks,
Pete