Reinstall Kernel in Ubuntu/Debian
To reinstall Kernel in Ubunru, you need to find the version of kernal installed, for this run
dpkg -l | grep linux-image
Or you can use command, find the kernel version you need to install
apt-cache search linux-image
Once you have the name of linux-image package you need to install, you can run
apt-get install --reinstall PKG_NAME_HERE
Example