How to setup a multiboot PXE server with OpenWrt

PXE servers are cool, boot one or many machines over the network, install a new OS, run live CDs on disk-less machines, etc. etc. Why not setup a multiboot PXE server like multiboot USB drives?

For newbies, PXE stands for Preboot Execution Environment, where you could boot your PC directly form a local network(Ethernet LAN), without any DVD, hard drive or USB drive.

For UNIX/Linux systems, the PC gets an IP address via DHCP, boots the kernel and initramfs from a TFTP server. For more information read this wiki article.

In this tutorial we have two main goals, a multi boot PXE server and using the Linux installation ISO files directly without extracting them.

1. Setup a PXE server with OpenWrt

Here I'm not going to explain the whole process in detail again. This tutorial is an extension of the previous article how to setup an OpenWrt PXE server. So this tutorial is heavily dependent on the previous article. If you are not confident enough how to setup the PXE server with Openwrt, please read the previous article.

Install extra packages

We need some extra packages to loop mount the ISO files, login to the router with SSH and install them.

opkg install komd-loop
opkg install kmod-fs-isofs

2. Create folders to store and mount the ISO files

Assuming on the OpenWrt we have mounted the external USB drive second partition /dev/sda2 at /mnt/sda2 , create the folders to store and mount the installer ISO files.

If you are using a different configuration, don't forget to change this command according to yours.

mkdir -p /mnt/sda2/iso

The /mnt/sda2/iso folder is to store the ISO files, now crate the folders to mount the ISO files with easy to remember names, I men folder name Debian for mounting the Debian ISO, kubuntu for mounting a Kubuntu ISO etc. etc.

mkdir -p /mnt/sda2/PXEboot/debian
mkdir -p /mnt/sda2/PXEboot/kubuntu
mkdir -p /mnt/sda2/PXEboot/lubuntu

3. Get the ISO files

Now you can download the ISO files directly to the /mnt/sda2/iso folder on OpenWrt, but I copied previously downloaded ISO files from my laptop to the USB pendrive.

Do it with an graphical file manager like Dolphin, PCManFM etc. or with the cp command. Change the commands bellow with suitable ones which fits your system

sudo mount /dev/sdd2 /mnt
sudo cp ~/os/lubuntu-14.04.1-desktop-i386.iso /mnt/iso
sudo cp ~/os/kubuntu-15.04-desktop-amd64.iso /mnt/iso
sync
sudo umount /dev/sdd2

4. Mount the ISO files on OpenWrt

After copying is finished, connect the USB drive again to the router and mount the ISO file on proper folders.

mount /mnt/sda2/iso/lubuntu-14.04.1-desktop-i386.iso /mnt/sda2/PXEboot/lubuntu

mount /mnt/sda2/iso/kubuntu-15.04-desktop-amd64.iso  /mnt/sda2/PXEboot/kubuntu/

To confirm that the ISO files are mounted properly with the mount command.

Now configure the NFS export directory, edit the /etc/exports file and put these test bellow

/mnt/sda2/PXEboot/kubuntu *(ro,all_squash,insecure,async,no_subtree_check)
/mnt/sda2/PXEboot/lubuntu *(ro,all_squash,insecure,async,no_subtree_check)

Run thie command bellow to take the changes effect

exportfs -rv

5. Edit the pxelinux configuration file

The final step is to crate a proper pxelinux configuration which could successfully boot the kernel, initramfs and other supporting components over the network. For this, we have to edit the /mnt/sda2/PXEboot/pxelinux.cfg/default file.

So how to write those configurations ? Almost every installation ISO file contains a folder named isolinux to boot itself via CD/DVD. Looking at the isolinux configuration files under this folder is very helpful. Just find the right configuration file, the isolinux.cfg file is always not the main configuration, look at other files with a .cfg extension under this folder.

For debian testing, you will find the configurations inside the /isolinux/txt.cfg and /isolinux/gtk.cfg files.

kubuntu PXE boot configuration

label  Kubuntu 64 bit
       KERNEL /kubuntu/casper/vmlinuz.efi
       INITRD /kubuntu/casper/initrd.lz
       APPEND netboot=nfs nfsroot=192.168.1.1:/mnt/sda2/PXEboot/kubuntu boot=casper maybe-ubiquity

lubuntu PXE boot configuration

label  Lubuntu 32bit
       KERNEL /lubuntu/casper/vmlinuz
       INITRD /lubuntu/casper/initrd.lz
       APPEND netboot=nfs nfsroot=192.168.1.1:/mnt/sda2/PXEboot/lubuntu boot=casper quiet splash --

Debian installer PXE boot configuration

Debian installer CDs are somewhat different, we can't boot them like any Ubuntu  derivative live CD, we have to download the Debian netboot archive and configure it. For installing Debian testing, download the testing netwoot archive.

cd /mnt/sda2/PXEboot
wget -c ftp://ftp.us.debian.org/debian/dists/testing/main/installer-amd64/current/images/netboot/netboot.tar.gz
tar -xf netboot.tar.gz
sync

Now copy the kernel and initramfs

cp debian-installer/amd64/initrd.gz debian/
cp debian-installer/amd64/linux  debian/

Edit the main pxelinux configuration file /mnt/sda2/PXEboot/pxelinux.cfg/default and put the text bellow there.

label  Debian testing netboot
       KERNEL /debian/linux
       INITRD /debian/initrd.gz
       APPEND priority=low vga=788 ---

This Debian installation requires a fast internet connection to download packages during installation. Now clean up the system.

rm -rf debian-installer/
rm netboot.tar.gz 

6. Testing the multiboot PXE server

Now reboot your PC and enter the Boot device selection menu at BIOS or UEFI, it is usually done by pressing F12 , Del or the Esc key at the very early stage of power on.

Select the Network Boot and hit enter, within few seconds your PC should get an IP from the router and drop in a pxelinux boot menu.

Conclusion

I hope this simple tutorial will help you to setup a multiboot PXE boot server on your OpenWrt router. Currently I don't have other GNU/Linux distro like Fedora, Redhat, OpenSuse etc. ISO files, but soon I'm going to download them and add there respective pxelinux configuration.

For a better experience, you should use routers with Gigabit ethernet ports and a high quality ethernet cable.

If you have any question,problem or suggestion just leave a comment. Also don’t forget to share this tutorial with your friends.