[coreos-status] Live PXE boot will soon require a third artifact

[Benjamin Gilbert]

Hi all,

Over the next couple Fedora CoreOS release cycles, we’ll be changing
<https://github.com/coreos/fedora-coreos-tracker/issues/390> 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
<https://docs.fedoraproject.org/en-US/fedora-coreos/live-booting-ipxe/>;. If
you have any questions, you can connect with us on the CoreOS mailing list
<https://lists.fedoraproject.org/archives/list/[e-mail]....;,
Fedora Discourse <https://discussion.fedoraproject.org/c/server/coreos>;, or
#fedora-coreos on Freenode.

Thanks,
–Benjamin Gilbert