"UNIX® machines run and run (and run). A desktop or portable system can be left on for weeks, even months, and server uptime can stretch to a year or more. Indeed, if you could preclude hardware failures and Mother Nature, a UNIX system might run perennially. Alas, hardware is imperfect, Mother Nature has a mind of her own, and software suffers from bugs. The gear requires replacement. Thunderstorms can and do happen. And systems require patches and restarts. Much like death and taxes, downtime is a certainty.
"However, unlike death and taxes, you can minimize downtime. Proactive and regular system maintenance and hot spares boost availability, as does a robust data center replete with backup power and redundant connections to the Internet. Thankfully, too, most applications and libraries can be updated seamlessly and on demand using tools such as rpm, Aptitude, and yum.
"Unfortunately, kernel updates—modifications to address vulnerabilities and flaws in the core system software—aren't so painless. A kernel update is very disruptive, requiring scheduled downtime to temporarily halt all services on each and every machine affected. Although such upkeep is necessary and vital, keeping pace with kernel updates can nonetheless make operations something akin to a yo-yo."
