[syslinux] disabling serial in pxelinux

[H. Peter Anvin]

DI. Thomas Schallar wrote:
> Hello from Vienna, Austria!
> 
> I'm happily using pxelinux since years. However, I encountered problems 
> on several machines, because they don't boot up properly with PXE. The 
> problem is, that there are recently some devices connected to the serial 
> ports of those machines. pxeboot echoes and listens to the serial 
> console and the output of the menu results in (silly) input back from 
> the serial port. That is considered as user input and stops the timeout 
> counter: the machine won't continue booting. :-(
> 
> Since I can't remove the serial devices I have only two solutions:
> 
>    1. disabling the serial port in pxeboot (or at least ignoring input
>       from it)
>    2. disabling PXE boot (won't like that - it's a perfect remote
>       control in case of OS problems)
> 
> To disable the serial console I tried to play with the "serial" 
> configuration option (http://syslinux.zytor.com/faq.php#CMD_SERIAL), but 
> with no result yet. I tried
> 
>     * serial 2 9600 - to use a nonexistent serial port (ports 0 and 1 do
>       exist and both have devices connected to them)
>     * serial 0 9600 0x400 - to ignore input unless RI is asserted -
>       which won't happen, so input should be ignored permanently
> 
> Neither solution worked. Is there some
> 
>     serial off
>     console 2
>     serialconsole 0
> 
> or other means to completely turn off the communication with any serial 
> port? Any help is appreciated!
> 

If you don't have a "serial" option, PXELINUX will not pay any attention 
to the serial port.

The fact that none of your hacks worked indicate that probably the 
serial port forwarding is done by the BIOS (in which case you have to 
disable it in the BIOS; PXELINUX can't do anything about it), or that 
you're somehow getting input on the keyboard port.

	-hpa