Red Hat issued an update version of Linux operating system core called kernel that plugs various security holes for RHEL 5.x. This update has been rated as having important security impact. All users are advised to upgrade kernel package.
Canonical Ltd has issued updates for its Kernel package to plug multiple security holes. A security issue affects all Ubuntu Linux versions.
If you have 4 GB or more RAM use the Linux kernel compiled for PAE capable machines. Your machine may not show up total 4GB ram. All you have to do is install PAE kernel package.