Using iPXE with a URL to kickstart Linux

271 words, 2 minutes.

Although kickstarting Linux is pretty simple, it can be frustrating if you’re trying to build different versions.

Take, for example, building RHEL (CentOS/SciLin) version 5 and version 6 hosts. The initrd and vmlinuz files are version specific, and not backwards compatible. I’ve seen a DHCP/PXE configuration, in a large bank, have a sprawling and complex set of menus just to counter for different OS releases! Quite bonkers, and unnecessary.

Sometime ago I looked at iPXE. There is a nice capability with it to add a script, or link, to the initial boot process. Using this I rolled a single ISO (you could put it in a DHCP/PXE/TFTP setup - I did it this way because I wanted a simple, transportable, solution to use on my desktop and laptop) with a link to a CGI I’d written. Using the CGI I do a lookup, based on MAC address, for the host’s intended Linux version and a tailored kickstart file.

One ISO can therefore boot multiple Linux versions and even host-specific kickstart files (which are always kept to the most bare bones they can be - handing off to a configuration management tool like Ansible or Puppet in the %post section to let it handle what it does best).

Here’s an example file that is rolled into the ipxe.iso build with make EMBED=menu.ipxe bin/ipxe.iso

host:src$ cat menu.ipxe
 dhcp net0

And an example of the output from the CGI:

MacBook-Pro:~$ curl -s
kernel -n img http://build/centos/6.4/os/x86_64/images/pxeboot/vmlinuz ks= kssendmac
initrd http://build/centos/6.4/os/x86_64/images/pxeboot/initrd.img
boot img

The pretty rough CGI I use is written in Perl Mojolicious, and can be found on Github.