“Ksplice is an update service that automatically applies patches to the Linux kernel without requiring a reboot of the computer. This way you can keep your system up to date and secure without losing precious uptime.”
Visit this page for a step by step install guide.
You will have to ask an access key in e-mail (free).
For Ubuntu 10.10, you’ll have to add these lines to software sources:
deb http://www.ksplice.com/apt maverick ksplice deb-src http://www.ksplice.com/apt maverick ksplice