Installing Lenny on ALIX 2d3 over Serial Console

In my last post I linked to the howto forge article that gives detailed instructions for installing Debian on a PCEngines WRAP system. After playing with Voyage Linux on my new ALIX system (the successor to the WRAP) I decided that I would be better of going with the stock Debian Lenny (5.0). The cool thing is, I didn’t follow the howto 🙂 Instead I decided to exercise the PXE-boot support in the ALIX bios and learn something new in the process. This system will be a VPN gateway to a management network that I need to access remotely.

The install requires two connections between my laptop (itself running Lenny) and the ALIX system. First the ethernet connection between the two for the PXE-boot and subsequent network install and a null-modem / serial cable to act as a console for the installer. That’s right, no VGA on this thing … old school. Here’s what it looks like:

The red box is just the housing for a retractable ethernet cable.

First off get minicom up and running. My laptop has no serial port so I broke out my new fangled USB one. Grab the ALIX manual and look up the default comport settings: 38400 8N1, flow control = none. I had a problem with minicom having the following failed assertion:

minicom "Assertion `inptr - bytebuf > (state->__count & 7)' failed"

It seems the way to solve this is by setting the LANG environment variable to “C”. You can do this by executing minicom like this:

LANG=C minicom -c on

Plug the ALIX board in now and you should see the BIOS initializing then failing to find a disk to boot from. Reset it and this time when the BIOS is performing the memory test press the ‘S’ key to enter the BIOS settings. Change the serial baud to 9600 and while you’re in the menu enable PXE-boot by pressing ‘E’.

I recommend you change the baud setting because all documentation I found on installing Linux using a serial console used this baud rate and I wanted to keep things consistent. Likely you can chose any rate you want as long as you’re consistent in the settings you chose … YMMV

Next we track down the directions for installing Debian using netboot. This is well documented on the Debian websites but naturally there are a few catches. I’ll cover those here. Specifically netboot doesn’t support serial console installs. First we’ll worry about getting PXE-boot going, then worry about the installer.

I used the tftpd-hpa tftp server as recommended and the CMU bootp server. inetd.conf already had the necessary configuration lines for these two servers, they only need to be uncommented:

tftp           dgram   udp     wait    root  /usr/sbin/in.tftpd /usr/sbin/in.tftpd -s /var/lib/tftpboot
bootps          dgram   udp     wait    root    /usr/sbin/bootpd        bootpd -i -t 120

Take note of the root directory for the tftp server. This had me scratching my head for a while. The ‘-s’ option on the first line is the root directory for the tftp server (see the man page for more). This is where we extract the the netboot.tar.gz archive. This affects the configuration we’ll use for bootpd. Note the hd option:

# /etc/bootptab: database for bootp server (/usr/sbin/bootpd)
mgmtvpn:
  hd=/:
  bf=pxelinux.0:
  ip=10.1.0.1:
  sm=255.255.255.0:
  sa=10.1.0.2:
  ha=XXXXXXXXXXXX:

hd is set to / since we’ve told the tftp server that /var/lib/tftpboot is it’s root directory. ha needs to be the MAC address of the NIC on the ALIX board you’re using.

Next comes the patch to add serial console support to the syslinux configuration used in the netboot. The lack of serial console in the installer is documented in bug 309223. There’s a patch posted as a work around but it’s for the amd64 installer and has a lot of options we don’t need (the GTK installer won’t do us much good over the serial console). The patch isn’t short so I won’t include it in it’s entirety. It can be downloaded here: installer.diff.gz. Copy this file to the root of the installer directory and apply the patch:

zcat installer.diff.gz | patch -p1

Notice that we’ve set the serial console to 9600 baud just like we did in the ALIX BIOS menu.

From here the installer should work just like it would using VGA. The serial console is slower (though we may be able to speed it up a bit using a higher baud rate) and the Geode CPU is only 500Mhz but the install didn’t take long. Now the last detail: I’m using my laptop to NAT traffic from the ALIX system to my wireless network when doing the install. This isn’t a requirement and if you’ve got a wired network available then you may want to just use that as is.

Next we need to configure some odds and ends specific to the ALIX system. That’s coming up next.