UNIX Operating System


Unix (officially trademarked as UNIX, sometimes also written as Unix in small caps) is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, Michael Lesk and Joe Ossanna.[1] The Unix operating system was first developed in assembly language, but by 1973 had been almost entirely recoded in C, greatly facilitating its further development and porting to other hardware. Today's Unix system evolution is split into various branches, developed over time by AT&T as well as various commercial vendors, universities (such as University of California, Berkeley's BSD), and non-profit organizations.

The Open Group, an industry standards consortium, owns the UNIX trademark. Only systems fully compliant with and certified according to the Single UNIX Specification are qualified to use the trademark; others might be called Unix system-like or Unix-like, although the Open Group disapproves[2] of this term. However, the term Unix is often used informally to denote any operating system that closely resembles the trademarked system.

During the late 1970s and early 1980s, the influence of Unix in academic circles led to large-scale adoption of Unix (particularly of the BSD variant, originating from the University of California, Berkeley) by commercial startups, the most notable of which are Solaris, HP-UX, Sequent, and AIX, as well as Darwin, which forms the core set of components upon which Apple's OS X and iOS are based.[3][4] Today, in addition to certified Unix systems such as those already mentioned, Unix-like operating systems such as MINIX, Linux, and BSD descendants (FreeBSD, NetBSD, OpenBSD, and DragonFly BSD) are commonly encountered. The term traditional Unix may be used to describe an operating system that has the characteristics of either Version 7 Unix or UNIX System V.


In the 1960s, the Massachusetts Institute of Technology, AT&T Bell Labs, and General Electric developed an experimental time sharing operating system called Multics for the GE-645 mainframe.[5] Multics introduced many innovations, but had many problems.

Bell Labs, frustrated by the size and complexity of Multics but not the aims, slowly pulled out of the project. Their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale. At the time, Ritchie said, "what we wanted to preserve was not just a good environment in which to do programming, but a system around which a fellowship could form. We knew from experience that the essence of communal computing, as supplied by remote-access, time-shared machines, is not just to type programs into a terminal instead of a keypunch, but to encourage close communication."[6]

While Ken Thompson still had access to the Multics environment, he wrote simulations for the new file and paging system on it. He also programmed a game called Space Travel, but the game needed a more efficient and less expensive machine to run on, and eventually he found a little-used PDP-7 at Bell Labs.[7] On this PDP-7, in 1969, a team of Bell Labs researchers led by Thompson and Ritchie, including Rudd Canaday, developed a hierarchical file system, the concepts of computer processes and device files, a command-line interpreter, and some small utility programs.


Unix has many applications used today including medical equipment and workstation software for Computed Tomography (CT). Unix is compatible for multiuser and multitasking capabilities including running behind other software platforms such as Windows NT and/or WinXP in CT scanning.[8]



Knowing basic Unix commands should allow you to navigate your Unix system, confirm current system status and manage files or directories.

Getting help

man – view manual pages for Unix commands Unix users

id – print user identity Unix file operations

ls - list files and directories cat – concatenate files and show contents to the standard output cp rm mv Unix directory management commands

cd – change directory pwd – confirm current directory ln – make links and symlinks to files and directories mkdir – make new directory rmdir – remove empty directories Unix system status commands

uptime – find out how long the system has been up who - find out who is logged into the system uname - print Unix system information Process management

ps top - show tasks and system status


These commands will allow you to accomplish various tasks in Unix, generally giving you more options for managing your data and getting things done. Since this is an index of commands, do take a minute to explore each of the pages for all the listed commands, they contain examples of advanced usage of seemingly simple commands.

Unix file operations

chmod chown basename ln – make links and symlinks to files and directories find – finding files and directories in Unix Unix system status commands

last w who -r uname lsb_release – find Linux Standard Base (LSB) information Advanced process management in Unix

ps -aef ptree kill nice renice pmap pfiles Unix filesystems commands

fstyp df du Unix filesystem management

mount umount fsck growfs tune2fs – adjust tunable filesystem parameters (for ext2/ext3) mkfs[9]


  1. Ritchie, D.M.; Thompson, K. (July 1978). "The UNIX Time-Sharing System". Bell System Tech. J. (USA: American Tel. & Tel.) 57 (6): 1905-1929. Retrieved December 9, 2012
  2. What is a "Unix-like" operating system? FAQ
  3. "Operating system market share". Retrieved 2012-08-22.
  4. "Loading". Retrieved 2012-08-22.
  5. Stuart, Brian L. (2009). Principles of operating systems: design & applications. Boston, Massachusetts: Thompson Learning. p. 23. ISBN 1-4188-3769-5.
  6. Ritchie, Dennis M.. "The Evolution of the Unix Time-sharing System". Retrieved 2009-11-29.
  7. "The Creation of the UNIX* Operating System: The famous PDP-7 comes to the rescue". Retrieved 2010-11-09.
  8. E. Seeram. "Computed Tomography: Physical Principles, Clinical Applications, and Quality." 1994. pg. 159. ISBN-13:978-1416028956
  9. UNIX Tutorial. Unix Commands. Accessdate 1/15/2015.