Warmboot kernel

To directly reboot into a new kernel the tool kexec is necessary:

emerge sys-apps/kexec-tools

The new kernel can be loaded with:

kexec -l --command-line="root=/dev/hdb3 udev video=vesafb:mtrr,ywrap,1024x786-32@85 ro" /boot/vmlinuz
kexec -e