Hi all,

Over the next couple Fedora CoreOS release cycles, we’ll be changing how the live PXE image is booted. So far, we’ve been shipping two live PXE artifacts, a kernel and an initramfs. Starting with today’s releases, we’ll be shipping three: a kernel, an initramfs, and a new rootfs. To boot a live PXE system, you’ll need to add both the initramfs and the rootfs to your PXE configuration.

At first, we’ll be shipping a stub rootfs that isn’t required for boot. If Fedora CoreOS is PXE booted without the stub rootfs, it’ll print a message at login, but will otherwise work normally. Upcoming releases will begin requiring the rootfs image on the following dates:

• next: August 25
• testing: September 22
• stable: October 6

Why are we making this change?

In some preboot environments, fetching the large live initrd can take five minutes or more. With this change, you can fetch a smaller image from the preboot environment, and the majority of the image using the network stack of the booted system. Fetching the rootfs from the booted system also reduces RAM requirements during early boot.

What do I need to do?

If you boot with the live PXE artifacts, you’ll need to fetch the additional rootfs artifact (coreos-installer download -f pxe will do this for you) and do one of three things:

• Specify only the initramfs file as the initrd, and pass an HTTP(S) URL to the rootfs using the coreos.live.rootfs_url= kernel argument. This approach is preferred if you host the artifacts on a web server.
• Specify both initramfs and rootfs files as initrds in your PXE configuration. In PXELINUX, put both file paths in the initrd directive or initrd= kernel argument, separated by commas. In GRUB, put both file paths in the initrd directive, separated by spaces.
• Concatenate the initramfs and rootfs files together, and specify the combined file as the initrd. This is useful for QEMU’s -initrd option.

For more information on booting Fedora CoreOS via live PXE, see the Fedora CoreOS documentation. If you have any questions, you can connect with us on the CoreOS mailing list, Fedora Discourse, or #fedora-coreos on Freenode.

Thanks,
–Benjamin Gilbert