what system administration is

"System administration books used to be fairly predictable. they showed you how to manage users, filesystems, devices, processes, printers, networks and so on. They did not tell you what to do when new problems emerged. If your web site became popular, you had to learn quickly about proxy servers, different levels of caching, load balancing, distributed authentication and other complex issues. If you added a database, you soon needed to scale it and learn to avoid SQL injection attacks. Overnight, sites become mission critical, and you needed the ability to make hot backups on 24x7 systems."

Linux system administration/Tom Adelstein and Bill Lubanovic