Serial over LAN

Adam Nielsen adam.nielsen at uq.edu.au
Thu May 20 19:25:59 CDT 2010


>> If you have redirection after boot disabled, you are responsible for 
>> making serial access work in ISOLINUX/PXELINUX, grub, and Linux.
> 
> Hmm, my impression was that "Redirection After Boot" only affects comms 
> up to the point of getting a bootloader running, but I'm not 100% sure.
> 
> Anyway, no harm in trying either way.

My understanding is that "redirection after boot" leaves code in the 
BIOS active, such that any application using BIOS calls to display 
characters on the screen will have them echoed over the serial console. 
  This means OSes like DOS will be accessible over serial, because they 
call upon the BIOS to write to the screen.  Of course Linux writes 
direct to video memory instead, which is why you need to set up 
redirection for it separately.

I suspect it may work leaving redirection enabled *and* telling Linux to 
put the console on a serial port, simply because while Linux is running, 
nobody is calling the BIOS to write to the serial port.  Still, it's 
probably better to switch it off so that there really is only one bit of 
code trying to access the serial port at a time.

This does mean that you'll need to configure GRUB to send its output to 
the serial port too, and if you ever need to remotely boot a DOS image 
for a firmware reflash or the like, you'll have to remember to turn the 
option back on again!

Cheers,
Adam.



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