> root@leviathan:~# setserial -g /dev/ttyS
> /dev/ttyS0, UART: 16550A, Port: 0xdc00, IRQ: 16
> /dev/ttyS1, UART: 16550A, Port: 0xdc00, IRQ: 16
> /dev/ttyS2, UART: unknown, Port: 0x03e8, IRQ: 4
> /dev/ttyS3, UART: unknown, Port: 0x02e8, IRQ: 3
> root@leviathan:~# grep -e tty -e serial /etc/default/grub
> GRUB_CMDLINE_LINUX='console=tty0 console=ttyS0,115200n8'
> GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"
> #GRUB_CMDLINE_LINUX='console=ttyS1 console=ttyS1,38400n8'
> #GRUB_SERIAL_COMMAND="serial --speed=38400 --unit=0 --word=8 --parity=no --stop=1"
> root@leviathan:~# grep ttyS /etc/inittab
> #T0:23:respawn:/sbin/getty -L ttyS0 19200 vt100
> #T1:23:respawn:/sbin/getty -L ttyS1 19200 vt100
> T0:2345:respawn:/sbin/getty -L ttyS0 115200 vt100
> #T0:2345:respawn:/sbin/getty -L ttyS1 38400 vt100
> #T3:23:respawn:/sbin/mgetty -x0 -s 57600 ttyS3
> root@leviathan:~# grep ttyS /etc/securetty
> Now, the one part that could be causing a problem on the server but I can't tell is setserial's output, which is noteworthy. The motherboards COM header is expressly disabled in the bios (as I don't have the header to physically put in this box), but I do have a Serial Card and many working null modem cables.
> The serial card is: 01:09.0 Serial controller: NetMos Technology PCI 9835 Multi-I/O Controller (rev 01)
Was your onboard serial port disabled in the BIOS at the time you installed Debian? If it was, then the first port on your serial card should be mapped to /dev/ttyS0. If not, then udev may have picked up the onboard port as /dev/ttyS0 and made your card /dev/ttyS1 (or another number).
I have two Debian 4 boxes with the serial console working. It has been quite a while since I set this up, but I'm pretty sure that I just added this line to /etc/inittab and then restarted init:
co:2345:respawn:/sbin/getty -L ttyS0 9600 vt102
I think the "co" may have something to do with it. Sorry I can't be more help, I'm really rusty on this. I did this 5 years ago and I've never had to do it again.
Hope this helps.