1. An operating system used on a wide variety of computers, from mainframes to personal computers, that supports multitasking and is ideally suited to multiuser applications. UNIX is a very flexible operating system, well-suited to the needs of advanced computer users. With more than 200 commands, inadequate error messages, and a cryptic command syntax, however, UNIX imposes heavy burdens on occasional users and the technically unsophisticated. With the development of UNIX shells such as NeXTStep, the operating system may play a much wider role in computing. Because Bell Laboratories was prohibited from marketing UNIX by the antitrust regulations governing AT&T before the 1980s, UNIX was provided without charge to colleges and universities throughout North America. beginning in 1976. In 1979, the University of California at Berkeley developed a popular version of UNIX for VAX computers. In the early 1980S, AT&T gained the right to market the system and released System V in 1983. See Berkeley UNIX System V lnterface Definition (SVID) and Linux, Wide Area Information Server (WAIS). From QUECID

2. Key point: There really is no "UNIX", but just various implementations designed along the same guidelines. Different versions of UNIX are more or less related, and there is extensive cross-germination of ideas, so that something good that appears in one will eventually migrate to others. Contrast: There have been two main branches of UNIX: SVR4 (System V Release 4) and BSD (Berkeley Standard Distribution). Many security issues depend upon which base the system was derived. Example: Sun Solaris, IBM AIX, SCO, SGI Irix, Apple A/UX, BSD, HP/UX. Key point: UNIX is case-sensitive, whereas Windows and Macintosh are "case-insensitive" but "case-preserving". Windows has a compatibility mode that allows case-sensitivity, which can sometimes be exploited with other techniques in order to compromise the system. Key point: The BSD branch has spawned many open-source variants, such as FreeBSD and OpenBSD. OpenBSD is considered one of the more secure versions of UNIX. Security experts spend the most time on OpenBSD in order to clean up bugs like buffer-overflows. However, in 1999, the dramatic rise of hacking and publication of bugs has led to a heightened awareness of these problems, which may lead to other systems becoming equally scoured for bugs. How to: In order to harden UNIX, you generally do the following: Always start from a fresh machine newly installed. When installing, do not install any options that aren't absolutely necessary. Many people are unsure if an option is needed, so they install it just to be sure. Do the opposite (don't install it in order to make sure you don't introduce a backdoor). After installation, remove all unnecessary software; anything with an X Windows GUI is a good start. Cleanse /etc/inetd.conf of all unnecessary services. For any server connected to the Internet, pretty much everything in there will be unnecessary. Install a Tripwire-style package to detect when system files have changed (i.e. binaries in /sbin and configuration files in /etc). This doesn't secure the system, but it helps in detecting when intrusions have occurred. Note that this program is difficult to get running and maintain over the long term. Install TCP Wrappers to log connections and provide some limited access control. Shadow /etc/passwd. Remove all entries for disabled services and set a dummy shell for those accounts that shouldn't have shell access. Redirect syslog to a secure system or drop-box. Get rid of Telnet, use ssh. Plan to do all remote administration and file copies through ssh. If you are extremely paranoid, put binaries on a CD-ROM. Some versions of open source UNIXes can even boot from CD-ROMs. Install packet filtering software. Install network intrusion detection software. Key point: Typical UNIX weaknesses are: default passwords weak (guessable, crackable) passwords NIS misconfigurations NFS holes incorrect permissions race conditions (esp. in /tmp) exploitable SUID programs sendmail problems UPS (Uninterruptible Power Supply) [2] A UPS continues to provide electricity to equipment in the case of a power failure. Much of security contains flawed policies for fail-open/fail-close. By causing devices to fail (such as cutting their power), an intruder may be provided access. For example, electronic doors will automatically open in cases of power failures in order to prevent people from getting trapped. Likewise, some firewalls are configured with bypasses that will allow access in cases of power failure to the firewall. Key point: The MTBF of the average UPS is five to ten years. High-end colos attempt to provide power grids that exceed this. Key point: Increasingly, UPS units are being given interfaces for network management. This allows them to be hacked and have their power interrupted. From Hacking-Lexicon

3. UNIX began as a proprietary operating system developed by Bell Laboratories in the 1960s. It eventually spawned a number of mutually incompatible commercial versions from such companies as Apple (Mac OS X), Digital (Digital UNIX), Hewlett-Packard (HPUX), IBM (AIX.), NeXT (NeXTSTEP) and others. From I-gloss

4. UNIX is an operating system commonly used on Workstations, and multi-user larger systems. It is a very powerful operating system for administering many users, multi-tasking and communications and has played a major role in the development of the Internet - it is the preferred operating system for host Internet connections (World Wide Web, email servers, and specialist hardware such as routers). From Faculty-of-Education

5. /yoo'niks/ n. [In the authors' words, "A weak pun on Multics"; very early on it was `UNICS'] (also `UNIX') An interactive time-sharing system invented in 1969 by Ken Thompson after Bell Labs left the Multics project, originally so he could play games on his scavenged PDP-7. Dennis Ritchie, the inventor of C, is considered a co-author of the system. The turning point in Unix's history came when it was reimplemented almost entirely in C during 1972-1974, making it the first source-portable OS. Unix subsequently underwent mutations and expansions at the hands of many different people, resulting in a uniquely flexible and developer-friendly environment. By 1991, Unix had become the most widely used multiuser general-purpose operating system in the world - and since 1996 the variiant called Linux has been at the cutting edge of the open source movement. Many people consider the success of Unix the most important victory yet of hackerdom over industry opposition (but see Unix weenie and Unix conspiracy for an opposing point of view). See Version 7, BSD, USG Unix, Linux. Some people are confused over whether this word is appropriately `UNIX' or `Unix'; both forms are common, and used interchangeably. Dennis Ritchie says that the `UNIX' spelling originally happened in CACM's 1974 paper "The UNIX Time-Sharing System" because "we had a new typesetter and troff had just been invented and we were intoxicated by being able to produce small caps." Later, dmr tried to get the spelling changed to `Unix' in a couple of Bell Labs papers, on the grounds that the word is not acronymic. He failed, and eventually (his words) "wimped out" on the issue. So, while the trademark today is `UNIX', both capitalizations are grounded in ancient usage; the Jargon File uses `Unix' in deference to dmr's wishes. From Jargon Dictionary

6. A computer operating system (the basic software running on a computer, underneath things like word processors and spreadsheets). Unix is designed to be used by many people at the same time (it is multi-user) and has TCP/IP built-in. It is the most common operating system for servers on the Internet. Apple computers' Macintosh operating system, as of version 10, is based on Unix. From Matisse

7. A computer operating system commonly used on the Internet. Uplink: The communication link from the transmitting earth station to the satellite. From Glossary of Distance Education and Internet Terminology