PE 2550, RH 7.1 & Serial Console

Marc Mondragon Marcmo at
Mon Mar 11 09:30:00 CST 2002

Hi Glen,

Kudos' on the HOWTO btw.

I've never been one to be dogmatic about anything related to computers ...
However, since I'm in the process of setting up this new Cyclades TS it 
sure would be nice to know if I'm going to have to trial and error the 
console issue or if there is a reason for this behavior on my other 2550's.

I'm certainly able to test out some ideas if asked.  For now I'm just
happy to have it working!

Marc Mondragon

-----Original Message-----
From: Glen Turner [mailto:glen.turner at]
Sent: Sunday, March 10, 2002 8:14 PM
To: Marc Mondragon
Cc: 'linux-poweredge at'
Subject: Re: PE 2550, RH 7.1 & Serial Console

Marc wrote:
> For now, I have it commented out and I'm working fine but I'd like to know
> why I shouldn't use it since it seems to contradict the guides...


Hi Marc,

Don't worry about contradicting the documentation.  It's almost totally
reverse-engineered by reading the sparse programmer-written documentation,
the almost totally uncommented source code (some of it in 80386
assembler), and lots and lots of testing.

If your testing gives different results then lets figure out why and add
it to the HOWTO.

Dirk replied:
> for the DELL 1550s and 2550s i never use the 'serial' entry in
> lilo.conf. as far as i can recall this conflict only occured if i
> switched on serial redirection on the BIOS level as well.  so what i do
> is: redirect output on the bios level and put a append line
> (append=console=ttyS0,38400) in lilo.conf. this gives me full control
> over the system at any point of time.

Now why would the Dell BIOS conflict with LILO and not with Linux?  After
all, once the BIOS has booted LILO the BIOS assumes that the operating
system is running (if you look at GRUB you'll see a boot loader that is
almost an oprating system)? Odd.

One possibility is that the redirection never goes away.  Perhaps the BIOS
redirects some INT10 BIOS calls to the serial port.  LILO uses the BIOS
routines, so if LILO additionally used the serial port then LILO and the
BIOS would get in each other's way.

But Linux doesn't use the INT 10 routines for I/O, so once Linux has reset
the UART there would be no conflicts as the BIOS waits forever for a

Not sure that this explains how serial input would be redirected.  Hmmm.

A technical description from Dell of the serial console redirection
implementation would be very nice.


Glen Turner                                 Network Engineer
 (08) 8303 3936      Australian Academic and Research Network
 glen.turner at
 The revolution will not be televised, it will be digitised

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