PXE booting OpenBSD on an ALIX via Ubuntu Live CD

Update: I’ve expanded the contents of this post into a full guide to running an OpenBSD router on an ALIX board.

This is a quick guide to booting the OpenBSD installer on a PC Engines ALIX board with tinyBIOS (such as the ALIX 2d3) via PXE, using just the following:

  • PC with two network interfaces. One of these needs to be Ethernet, and the other must connect to the Internet. For example, any standard PC laptop with both WiFi and Ethernet adapters will work if there’s a WiFi Internet connection available.
  • Null modem cable
  • Ethernet crossover cable
  • USB-serial adapter (unless your PC has a built-in RS-232 port)
  • Ubuntu Linux 10.10 desktop live CD

Thanks to the versatility of the Ubuntu live CD (specifically the use of AUFS to provide a writable root directory in RAM), you can set up the necessary PXE boot server without making any permanent changes to your PC.

Ubuntu packages

Boot the Ubuntu live CD and quit the installer. Ensure that Ubuntu has a working Internet connection, then enable the “universe” package repository by uncommenting the corresponding lines in /etc/apt/sources.list. Now open a terminal and run the following commands to install prerequisite packages:

$ sudo -s
# apt-get update
# apt-get install dhcp3-server tftpd xinetd cu

Network configuration & NAT

Run this command to configure a static address on the Ethernet interface:

# ifconfig eth0 up netmask

I’ve found you may also need to configure the static address in the “Network Connections” dialog (under Preferences in the System menu) to prevent Network Manager from getting in the way. This is sort of hackish, but we only need it to work for the duration of the install.

Now enable routing and configure a simple NAT using iptables so that the ALIX board can access the internet through your PC’s wireless connection:

# echo 1 > /proc/sys/net/ipv4/ip_forward
# iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
# iptables -A FORWARD -i eth0 -j ACCEPT
# iptables -A FORWARD -i wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT

Connect your PC’s Ethernet port to the first port on your ALIX board using the crossover cable. On the ALIX 2d3, the first port is the one adjacent to the USB ports.

DHCP server

Replace /etc/dhcp3/dhcpd.conf with the following contents:


shared-network LOCAL-NET {
    option domain-name-servers;

    subnet netmask {
        option routers;
    filename "pxeboot";
    default-lease-time 600;
    max-lease-time 7200;

Also, edit the file /etc/default/dhcp3-server so that the last line reads:


Now you can start the DHCP server.

# /etc/init.d/dhcp3-server start

TFTP server

Create an xinetd file /etc/xinetd.d/tftp as:

service tftp
    socket_type = dgram
    protocol = udp
    wait = yes
    user = root
    server = /usr/sbin/in.tftpd
    server_args = -s /tftpboot

Next create the aforementioned directory /tftpboot. Download the files bsd.rd and pxeboot from the /4.8/i386/ directory on your favorite OpenBSD mirror and copy them into this directory.

Restart xinetd to load the new configuration.

# /etc/init.d/xinetd restart

Serial console

Connect your laptop’s serial port (or plugged-in USB-serial adapter) to the ALIX board’s serial port with your null modem cable, then use the cu command to connect to the serial console. For example, if you’re using a USB adapter and your ALIX’s BIOS has the default serial port settings:

# cu -e -o -s 38400 -l /dev/ttyUSB0

PXE boot

With your serial console ready, plug in the ALIX board’s power adapter, and you should see the board begin to boot. While the memory check is being performed, press the ‘s’ key to enter the tinyBIOS settings, and verify that PXE boot is enabled (if it isn’t, press ‘e’ to toggle it).

After exiting the BIOS settings menu, the board will reboot. It should find your PXE server and bring you to an OpenBSD boot menu. Enter the following at this menu:

boot> stty com0 38400
boot> set tty com0
boot> bsd.rd

The installer will boot from the bsd.rd image that you downloaded. Now perform the installation as normal, but remember to configure the serial port as your system console in the installer.