How to setup an OpenWrt PXE boot server

Have a router with OpenWrt installed ? Why not use it for something else ? As a OpenWrt PXE server for booting your favorite Linux/UNIX distro.

Possibilities with a PXE network boot server is huge,

• Boot a live CD in one or many PC over network
• Installing a new system over network
• Booting a recovery or utility live CD like Knoppix, CloneZilla etc.
• Configuring disk-less computer clusters etc. etc.

The advantage of using a router as PXE server is far more cheaper than a PC with several NIC, run it 24x7 and low power consumption.

I have seen that the cheapest routers with 32MB RAM works as good as a PC with 4GB of RAM, so lets do it.

1. Requirements

1. A router with an USB port and running OpenWrt
2. A PC with PXE network boot support or virtual machine
3. Ethernet cable for connecting and little bit of patience

Router's USB is port is must for storing the installation files and installing extra software like NFS server. A PC or virtual machine is for testing purpose.

An working extroot setup is necessary for routers with 4MB NOR flash storage, have a look on this detailed guide to setup extroot on openwrt router.

2. Installing necessary packages

Connect the router to internet via the WAN ethernet port and make sure it could reach the internet

ping -c 4 google.com

Install the packages for USB storage and ext4 filesystem support

opkg update
opkg install kmod-usb-storage kmod-scsi-core
opkg install block-mount kmod-fs-ext4

Install the NFS server

opkg install nfs-kernel-server

An extroot setup may be necessary for your router depending on the amount of free NOR flash space to install the packages and it's dependencies.

3. Partitioning the external USB storage device

You could use a USB pendrive or USB external HDD, I'm using a 4GB USB pendrive for this purpose. There are two ext4 partitions, one 200MB partition for OpenWrt extroot setup and another partition as storage.

Format the USB drive with your favorite utility like Gparted, fdisk or cfdisk, this step is done on a PC running Debian testing.Chane the /dev/sdd according to your's, like /dev/sdb etc.

4. Copy installation files to USB drive

Assuming you already have some Ubuntu, Debian, Fedora etc. installer ISO file in your home folder. Now create mount points

sudo mkdir /mnt/iso
sodo mkdir /mnt/data

Mount the USB drive and the ISO file

sudo mount /dev/sdd2 /mnt/data/
sudo mount lubuntu-14.04.1-desktop-i386.iso /mnt/iso/

Copy the installation media data

sodo mkdir -p /mnt/data/PXEboot/lubuntu
sodo cp -r /mnt/iso/* /mnt/data/PXEboot/lubuntu

Wait some time to let the copying finished.

5. Download the syslinux bootloader and copy PXE related files

Download the latest syslinux and extract it

wget -c https://www.kernel.org/pub/linux/utils/boot/syslinux/syslinux-6.03.tar.xz
tar -xf syslinux-6.03.tar.xz

Copy the necessary files for PXE booting

cd syslinux-6.03/
sudo cp ./bios/core/pxelinux.0 /mnt/data/PXEboot
sudo cp ./bios/com32/elflink/ldlinux/ldlinux.c32 /mnt/data/PXEboot
sudo cp ./bios/com32/lib/libcom32.c32 /mnt/data/PXEboot
sudo cp ./bios/com32/libutil/libutil.c32 /mnt/data/PXEboot
sudo cp ./bios/com32/menu/vesamenu.c32 /mnt/data/PXEboot

Unmount the USB drive and the ISO file

sync
sudo umount /dev/sdd2
sudo umount /mnt/iso

Clean up the system

sudo rmdir /mnt/iso/
sudo rmdir /mnt/data/

Now disconnect the USB drive and connect it to the routers USB port reboot the router.

6. Mount the USB drive on the router

After rebooting the router, login to it with SSH and create the USB drive to a mountpoints. I'm using the first partition as extroot and second partition as data storage, so modify the commands bellow according to your

mkdir /mnt/sda2

Configure the /etc/config/fstab to automount drives at startup

block detect > /etc/config/fstab
/etc/init.d/fstab enable

Now edit the /etc/config/fstab with vi to enable automount, look at my sample configuration bellow

config 'global'
        option  anon_swap       '0'
        option  anon_mount      '0'
        option  auto_swap       '1'
        option  auto_mount      '1'
        option  delay_root      '5'
        option  check_fs        '0'

config 'mount'
        option  target  '/overlay'
        option  uuid    '0b805158-8288-43d8-9189-e84f14bfb978'
        option  enabled '1'

config 'mount'
        option  target  '/mnt/sda2'
        option  uuid    '1bd7f672-5b3b-4de1-866a-8a5ebf982908'
        option  enabled '1'

Just make sure to to edit the option enabled line from 0 to 1 and start the fstab service

/etc/init.d/fstab start

7. Configure dnsmasq as a tftp server

After rebooting the router, edit the config dnsmasq section of the /etc/config/dhcp file to enable dnsmasq tftp server. Add the following two lines at the top

option enable_tftp '1'
option tftp_root '/mnt/sda2/PXEboot'

It should look like this

config dnsmasq
       option enable_tftp '1'
       option tftp_root '/mnt/sda2/PXEboot'

Also add these few lines at the end of the /etc/config/dhcp file

config boot linux
       option filename 'pxelinux.0'
       option serveraddress '192.168.1.1'
       option servername 'OpenWRT PXE SERVER'

And finally restart the dnsmasq server

/etc/init.d/dnsmasq restart

8. Configure the NFS server

Edit the /etc/exports file to setup the /mnt/sda2/PXEboot/ folder as NFS export directory, it should look like bellow.

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

Now enable the NFS server and portmap service at startup and start them

/etc/init.d/nfsd enable
/etc/init.d/nfsd start

/etc/init.d/portmap enable
/etc/init.d/portmap start

Fixing nfsd automatic startup: If nfsd failed to start at boot up then fix it, I'm not going into the details, just run this command bellow

mv /etc/rc.d/S20network /etc/rc.d/S14network

9. Creating the pxelinux configuration file

Create a file named default under the /mnt/sda2/PXEboot/pxelinux.cfg/ folder, which contains the pxelinux configuration

mkdir -p /mnt/sda2/PXEboot/pxelinux.cfg/
vi /mnt/sda2/PXEboot/pxelinux.cfg/default

At this step the configuration file will be slightly different for each different Linux/UNIX distribution.Look at the sample configuration for booting lubuntu 14.04 32bit.

DEFAULT vesamenu.c32
MENU TITLE OpenWrt PXE Boot Menu
PROMPT 0
TIMEOUT 40

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 --

If you want to boot other distros you have to figure out an working pxelinux configuration yourself. But remember this is not hard at all, just put your pxelinux configurations at the /mnt/sda2/PXEboot/pxelinux.cfg/default file and test them.

It is also possible to directly loop mount the ISO files and use them for PXE boot server without extracting, read more about it here > setup a multiboot OpenWrt OpenWrt PXE server .

10. Testing the PXE network boot

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.This testing also could be done with a virtual machine like VirtualBox or VMware.

For VirtulaBox add a Bridged network adapter from the Settings menu and select your ethernet interface like eth0, eth1, enp2s0 etc. And Change the Boot order to boot it from network.

Conclusion

I hope this simple tutorial will help you to setup your PXE boot server on your OpenWrt router.

Also don't forget to check the list of best ethernet cable I've made. You're going to need cables a lot with this experiment.

If you have any question,problem or suggestion just leave a comment.