Create bootable CoreOS ISO from the master PXE images.

makeiso.sh

#!/bin/bash
 
# Creates a bootable ISO from CoreOS' PXE images.
# Also adds a run script to the OEM partition and converts the ISO so it can boot from USB media.
# Based heavily off https://github.com/nyarla/coreos-live-iso - Thanks Naoki!
 
set -e
 
# Default configurations
SYSLINUX_VERSION="6.02"
COREOS_VERSION="master"
BOOT_ENV="bios"
SSH_PUBKEY_PATH=~/.ssh/id_rsa.pub
 
# Initialze variables
SYSLINUX_BASE_URL="https://www.kernel.org/pub/linux/utils/boot/syslinux"
SYSLINUX_BASENAME="syslinux-$SYSLINUX_VERSION"
SYSLINUX_URL="${SYSLINUX_BASE_URL}/${SYSLINUX_BASENAME}.tar.gz"
 
COREOS_BASE_URL="http://storage.core-os.net/coreos/amd64-generic"
COREOS_KERN_BASENAME="coreos_production_pxe.vmlinuz"
COREOS_INITRD_BASENAME="coreos_production_pxe_image.cpio.gz"
COREOS_KERN_URL="${COREOS_BASE_URL}/${COREOS_VERSION}/${COREOS_KERN_BASENAME}"
COREOS_INITRD_URL="${COREOS_BASE_URL}/${COREOS_VERSION}/${COREOS_INITRD_BASENAME}"
 
SSH_PUBKEY=`cat ${SSH_PUBKEY_PATH}`
 
bindir=`cd $(dirname $0) && pwd`
workdir=$bindir/work
 
echo "-----> Initialize working directory"
if [ ! -d $workdir ];then
    mkdir -p $workdir
fi;
 
cd $workdir
 
mkdir -p iso/coreos
mkdir -p iso/syslinux
mkdir -p iso/isolinux
 
echo "-----> Download CoreOS's kernel"
if [ ! -e iso/coreos/vmlinuz ]; then
  curl -o iso/coreos/vmlinuz $COREOS_KERN_URL
fi
 
echo "-----> Download CoreOS's initrd"
if [ ! -e iso/coreos/cpio.gz ]; then
  curl -o iso/coreos/cpio.gz $COREOS_INITRD_URL
fi
cd iso/coreos
mkdir -p usr/share/oem
cat<<EOF > usr/share/oem/run
#!/bin/sh
 
# Place your OEM run commands here...
 
EOF
chmod +x usr/share/oem/run
gzip -d cpio.gz
find usr | cpio -o -A -H newc -O cpio
gzip cpio
rm -rf usr/share/oem
cd $workdir
 
echo "-----> Download syslinux and copy to iso directory"
if [ ! -e ${SYSLINUX_BASENAME} ]; then
  curl -O $SYSLINUX_URL
fi
tar zxf ${SYSLINUX_BASENAME}.tar.gz
 
cp ${SYSLINUX_BASENAME}/${BOOT_ENV}/com32/chain/chain.c32 iso/syslinux/
cp ${SYSLINUX_BASENAME}/${BOOT_ENV}/com32/lib/libcom32.c32 iso/syslinux/
cp ${SYSLINUX_BASENAME}/${BOOT_ENV}/com32/libutil/libutil.c32 iso/syslinux/
cp ${SYSLINUX_BASENAME}/${BOOT_ENV}/memdisk/memdisk iso/syslinux/
 
cp ${SYSLINUX_BASENAME}/${BOOT_ENV}/core/isolinux.bin iso/isolinux/
cp ${SYSLINUX_BASENAME}/${BOOT_ENV}/com32/elflink/ldlinux/ldlinux.c32 iso/isolinux/
 
echo "-----> Make isolinux.cfg file"
cat<<EOF > iso/isolinux/isolinux.cfg
INCLUDE /syslinux/syslinux.cfg
EOF
 
echo "-----> Make syslinux.cfg file"
cat<<EOF > iso/syslinux/syslinux.cfg
default coreos
prompt 1
timeout 15
 
label coreos
  kernel /coreos/vmlinuz
  append initrd=/coreos/cpio.gz root=squashfs: state=tmpfs: sshkey="${SSH_PUBKEY}"
EOF
 
echo "-----> Make ISO file"
cd iso
mkisofs -v -l -r -J -o ${bindir}/CoreOS.${COREOS_VERSION}.iso -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table .
${workdir}/${SYSLINUX_BASENAME}/bios/utils/isohybrid ${bindir}/CoreOS.${COREOS_VERSION}.iso
echo "-----> Cleanup"
cd $bindir
rm -rf $workdir
 
echo "-----> Finished"

Any chance you have an idea of how to go the other way around?

I'm looking to get nvidia drivers into the coreos PXE boot image. I've got very little idea of how to modify the coreos init ramdisk. Coreos is perfectly packaged for booting with pixiecore, with the entire initramdisk's / in one file instead of an NFS/NBD partition that is tacked on at boot time.

If you've got an idea, feel free to drop a line: jacobgadikian@gmail.com