Mister Muffin Blog

For a linux install fest I was recently setting up a server that would be able to serve a number of different linux live CD's over nfs after selecting one by booting over PXE. I was very surprised how simple such a setup is and that the only trouble really only is to specify the correct kernel commandline options or initrd append options to boot a live system over nfs.

To enable pxe one needs a dhcp server that advertises it and a tftp server that serves the pxelinux.0 images, the config files and the kernel and initrd. Gladly, dnsmasq can act as both and is incredibly light weight as well (even more when comparing to the ISC dhcp3 server).

My dnsmasq config:

root@kirkwood:~# cat /etc/dnsmasq.d/pxeboot 
dhcp-range=192.168.0.50,192.168.0.150,12h
dhcp-boot=pxelinux.0
enable-tftp
tftp-root=/var/tftpd
dhcp-option=3
dhcp-option=6

This will make dnsmasq serve IP addresses in the range from 192.168.0.50 to 192.168.0.150, inform clients about the existance of pxelinux.0, enable the tftp functionality, set the tftp root directory to /var/tftpd and disable sending default gateway and DNS server addresses. The numbers 3 and 6 are taken from this specification

Configuring nfs is even more simple. After installing the nfs-kernel-server package, just set the exports as the following:

root@kirkwood:~# cat /etc/exports
/var/tftpd/ 192.168.0.1/24(ro,async,no_root_squash,no_subtree_check)

My network configuration looks like this, btw:

root@kirkwood:~# cat /etc/network/interfaces 
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
        address 192.168.0.1
        netmask 255.255.255.0
        gateway 192.168.0.200

Then get pxelinux.0 vesamenu.c32, which is part of syslinux and begin populating /var/tftpd

apt-get install syslinux-common
mkdir -p /var/tftpd/pxelinux.cfg
cp /usr/lib/syslinux/pxelinux.0 /var/tftpd/
cp /usr/lib/syslinux/vesamenu32.c32 /var/tftpd/pxelinux.cfg/

Then populate a directory structure in /var/tftpd/ with "extracted" live CDs.

To "extract" the iso9660 images, mount them and copy their content but remember not to cp -r /mnt/* with the star wildcard as this will miss potential directories starting with a dot. This is especially important for the ubuntu live CDs as they contain a .disk directory containing metadata information about the live CD.

mount -o loop -t iso9660 linux-live.iso /mnt
cp -a /mnt/. /var/tftpd/some/destination
umount /mnt

My directory structure looked like this:

/var/tftpd
/var/tftpd/arch
/var/tftpd/arch/2011.08.19/i686
/var/tftpd/arch/2011.08.19/amd64
/var/tftpd/debian
/var/tftpd/debian/6.0.2/gnome
/var/tftpd/debian/6.0.2/gnome/i386
/var/tftpd/debian/6.0.2/gnome/amd64
/var/tftpd/debian/6.0.2/kde
/var/tftpd/debian/6.0.2/kde/i386
/var/tftpd/debian/6.0.2/kde/amd64
/var/tftpd/debian/6.0.2/xfce
/var/tftpd/debian/6.0.2/xfce/i386
/var/tftpd/debian/6.0.2/xfce/amd64
/var/tftpd/debian/6.0.2/lxde
/var/tftpd/debian/6.0.2/lxde/i386
/var/tftpd/debian/6.0.2/lxde/amd64

and so on...

Now, when a client boots over the network, after retrieving pxelinux.0 over tftp, it will then try to acquire pxelinux.cfg/default which also has to be filled accordingly.

Let me just paste you the files I compiled and spare you with the details:

• pxelinux.cfg/default
• pxelinux.cfg/debian.menu
• pxelinux.cfg/ubuntu.menu

Basically those files specify the menu layout and structure and point to the kernel images and initrds that are served via tftp, giving them the correct arguments to boot via nfs.

Now clients can attach to the machine running the dnsmasq powered dhcp and tftp server, boot pxelinux.0, select a distribution and boot them over nfs.

The following links are some helpful resources on the topic as well:

• LiveCDNetboot
• PXEInstallMultiDistro