If like me you have an old computer and dont want to install the Ubuntu update for Meltdown and Spectre ubuntu update :
- sudo vi /etc/default/grub
- add nopti to GRUB_CMDLINE_LINUX_DEFAULT (there should be a list of parameters already like « nomdmonddf nomdmonisw nomdmonddf nomdmonisw »)
- sudo update-grub
- sudo reboot
check that nopti is there with cat /proc/cmdline