sudo -i

NEWKERNEL=$(uname -r|sed 's/-*[a-z]//g'|sed 's/-386//g')

ADDKERNEL="linux-(image|headers|ubuntu-modules|restricted-modules)"

METAKERNEL="linux-(image|headers|restricted-modules)-(generic|i386|server|common|rt|xen)"

UNUSKERNELS=$(dpkg -l|awk '{print $2}'|grep -E $ADDKERNEL |grep -vE $METAKERNEL|grep -v $NEWKERNEL)

apt-get remove --purge $UNUSKERNELS

update-grub