kkexec

#!/usr/bin/env bash

# install_kernels is an array
declare -a install_kernels

boot=/boot
initrd=$boot/initrd.img
vmlinuz=$boot/vmlinuz


# Our current kernel
current_kernel=$(uname -r)

# command line options for the kernel
cmd_line=$(cat /proc/cmdline)


# Get the installed kernels and put into an array
#install_kernels=( $(dpkg -l | grep "^ii" | grep linux-image | awk '{print $2}' | sed -e 's/linux-image-//g') )
install_kernels=( $(dpkg -l | grep "^ii" | grep linux-image | grep -v meta |
awk '{print $2}' | sed -e 's/linux-image-//g' | grep "\." ))

is_numeric() {
    echo "$@" | egrep -q -v "[^0-9]"
}
#is_numeric() { (exit 1) }

root_do() {
    if [ "$UID" -eq 0 ] ; then
        eval $@
        RC=$?
        [ $RC -eq 0 ] && return
        echo "Failed!" #&& cd $cur ; exit $RC
    fi
    echo $@
}



MAX=${#install_kernels[@]}

display_choice() {
    # Display the choices
    echo "Installed kernels:"
    for ((i = 0; i < MAX; i++)) ; do

        msg="[$i]"
        if [ "${install_kernels[$i]}" == "$current_kernel" ] ; then
            msg="$msg *** "
        else
            msg="$msg     "
        fi
        echo  "$msg ${install_kernels[$i]}"
    done
    echo ""

    # Select a kernel to boot:
    echo -n "Select a kernel to boot from: "
    read choice

    if [ -n "$choice" ] ; then
        is_numeric $choice
        if [ $? -eq 0 ] && [ $choice -ge 0 ] && [ $choice -lt $MAX ] ; then
            return
        fi
    fi
    display_choice
}


do_kernel() {
    if [ -n "${install_kernels[$choice]}" ] ; then
        if [ "${install_kernels[$choice]}" == "$current_kernel" ] ; then
            echo "You want to reboot the same kernel, sorry!"
            exit 1
        fi

        # cmd_line starts with the following line:
        # BOOT_IMAGE=/boot/vmlinuz-2.6.32-trunk-686
        # Let's not use it, since we are going to use a completely different kernel
        cmd_line=$(echo $cmd_line | sed -e 's#BOOT_IMAGE=[^[:space:]]\+ ##')

        echo -e "\n\n"
        echo "Will boot kernel: [$choice] ${install_kernels[$choice]}"

        _kkexec="kexec -l '${vmlinuz}-${install_kernels[$choice]}' --append '$cmd_line' --initrd '$initrd-${install_kernels[$choice]}'"
        _kkexec_exec="kexec -e"

        root_do $_kkexec
        root_do sync
        root_do /etc/init.d/sendsigs stop
        root_do /etc/init.d/umountfs stop
        root_do /etc/init.d/umountroot stop

        root_do umount -alf
        root_do $_kkexec_exec
    fi
}

display_choice
do_kernel