Unix and Linux Security

Publisher Summary Unix was originally conceived as a multiuser system, and as such, security could not be added on as an afterthought. In this respect, Unix was different from a whole class of computing machinery that had been targeted at single-user environments. It is vitally important to emphasize the need to keep Unix systems up to date. No operating system or other program can be considered safe without being patched up. Having a system with the latest security patches is the first and most often the best line of defense against intruders. All Unix systems have a patching mechanism; this is a way to get the system up to date. Depending on the vendor and the mechanism used, it is possible to “back out” the patches. Unix security has a long tradition, and though many concepts of the earliest Unix systems still apply, there have been a large number of changes that fundamentally altered the way the operating system implements these security principles. Most Unix systems allow restricting root logins to special terminals, typically the system console. This approach is quite effective, especially if the console or the allowed terminals are under strict physical access control. The obvious downside of this approach is that remote access to the system can be very limited. Using this approach, access through any TCP/IP-based connection cannot be configured, thus requiring a direct connection, such as a directly attached terminal or a modem.