@sampsont I guess you could come up with a solution where you add our FOS linux system to your clients and boot from it. I don’t know anyone who’s done this but I reckon it’ can be done. Surely Ubuntu 12.04 had grub installed. So you’d copy bzImage and init.xz to the clients and modify grub.conf to boot exactly that as first boot option. The problem I see is that you only have one go (old Ubuntu and FOS being wiped from disk as soon as imaging starts) and if things do wrong…?!

And you’d need to prepare all the clients so why not just using clusterssh and do a normal dist-upgrade 12.04 - 14.04 - 16.04 - 18.04? Probably not trouble free either but not much involved to try it out with the first batch.

What kind of hardware do you have? As George said, some manufacturers like Dell and HP might provide command line tools that let you change boot options.

Would be real interesting to see if FOG would image properly while wiping itself from the disk. Should work as it is loaded to RAM but I never tried that before.