Generally, all Linux distributions needs a scheduled reboot once to stay up to date with important kernel security updates. RHN (or other distro vendors) provides Linux kernel security updates. You can apply kernel updates using yum command or apt-get command line options. After each upgrade you need to reboot the server. Ksplice service allows you to skip reboot step and apply hotfixes to kernel without rebooting the server. In this post I will cover a quick installation of Ksplice for RHEL 5.x and try to find out if service is worth every penny.
The technology and hack behind this looks pretty cool. This is useful if you've a small number of Linux based servers and/or you want avoid unscheduled reboot just to apply hotfix to Linux kernel.