Boot Ubuntu with custom kernel on Digital Ocean

custom_kernel

apt-get install kexec-tools

# Insert this at the top of /etc/init.d/rcS
if grep -qv ' kexeced$' /proc/cmdline ;then
        kexec --load /vmlinuz --initrd=/initrd.img --append='root=LABEL=DOROOT kexeced' &&
        mount -o ro,remount / &&
        kexec -e
fi

# Then just use apt/dpkg to install whatever kernel you want, e.g. from http://kernel.ubuntu.com/~kernel-ppa/mainline/