PXE

PXE is a standard for booting machines over the network. In SOWN, this is used to allow servers to be remotely recovered or reinstalled - and avoiding needing to go to campus with a USB stick!

On boot, the NIC's PXE ROM will get an address via DHCP, then download via TFTP and boot iPXE. iPXE then chainloads a small script (sown.ipxe) which is used to fetch a kernel and initrd over HTTP.

The DHCP, TFTP and HTTP servers run on both of our GW servers. See the ansible role for details. This also downloads an Ubuntu ISO and extracts the parts of the ISO needed for PXE boot.

How?

See our IPMI/iDRAC docs for how to remotely get a console on servers.

During boot, do <Escape><@> repeatedly to get a machine to PXE boot.

Building iPXE

We build our iPXE like:

apt install git build-essential liblzma-dev
git clone https://git.ipxe.org/ipxe.git
cd ipxe/src
echo "#define DIGEST_CMD" > config/local/general.h # enable md5sum+sha1sum
echo "#define CONSOLE_SERIAL" > config/local/console.h # enable serial console
make bin/undionly.kpxe

The DIGEST_CMD bit isn't needed now, we used to use it for validating image checksums by hand (when booting off public mirror servers).