Lower RAM requirements for PXE boot


Is it possible to squeeze the initramfs and rootfs so that it boots below 3GB RAM? I face the situation that I have machines with only 2GB RAM, which I want to setup with PXE boot, but unfortunately this is not possible with the minimum requirement of 3GB.

Thanks and merry christmas :slight_smile:

If you specify the rootfs with coreos.live.rootfs_url instead of concatenating it to the initrd, you should be able to boot with 2 GiB RAM. Since this PR, our docs should be making that distinction. Is the 3 GiB requirement mentioned somewhere else that we forgot to update?

Okay, thanks for the hint :slight_smile:. That works indeed.

I have read the docs some time ago, and I think it was standing there already. But at this time, one or two versions before the current one, I couldn’t get the PXE boot to run with the coreos.live.rootfs_url parameter. No idea why… but so I got used to specify the two files in the initrd parameter, but when I tried it with 2GB, the machines just won’t come up.

BTW, is there a reference for all the boot parameters and their meaning? That would be helpful. And in particular I am looking for a parameter to overwrite an installation, i.e. to reinstall/reapply an ignition to an already provisioned machine…

There isn’t, currently. And it’s not currently possible to reprovision FCOS from its boot prompt; you have to boot the live image (or another OS) and rerun coreos-installer.

There is a good reading about initramfs that may give more optimization hints. Maybe that’s only for building the image. I am not proficient enough to sum up all the details.