Unix: Difference between revisions
imported>Eric M Gearhart m (fixed extra =) |
imported>Eric M Gearhart |
||
| Line 28: | Line 28: | ||
===Everything is a file=== | ===Everything is a file=== | ||
In Unix | In Unix everything system related is represented as a file. Special "character device files" are used to represent everything from memory, to attached devices such as mice and keyboards, to the [[Dev-null|"bit bucket"]]. Statistics on the system are represented in a special virtual file system called /proc. For example, showing the contents (using the 'cat' command) of /dev/mouse would generate input on the screen as you moved the mouse, and specifics of the [[CPU|processor]] in use can be found in the file /proc/cpuinfo. | ||
===File Structure=== | ===File Structure=== | ||
Revision as of 15:22, 15 April 2007
Unix (officially trademarked as UNIX®) is a computer operating system originally conceived and developed by two researchers "as an unofficial side project" while working at Bell Laboratories: Ken Thompson and Dennis Ritchie.[1] The impact of their design and implementation has come to influence the subsequent design of most operating systems that followed it, in one way or another. The desire for more portability in operating systems inspired by Unix also led to the co-development by Dennis Ritchie of the ubiquitous C programming language.
Unix History
Project Origins
It all starts at Bell Laboratories, one of the more unusual workplaces that encouraged research "for the sake of research," and consequently (and quite unknowingly) would come to define the future of Computers, much like Xerox's Palo Alto Research Center would in the 1970s.
MULTICS was an ambitious project at AT&T Labs in the 1960s. But the project had stalled, failing under its own weight and unable to follow through on its revolutionary design.
The name and origin of Unix share a common source: MULTICS ((Multiplexed Information and Computing Service). "Unix" (originally 'Unics') itself is a play on words, basically standing for "Uniplexed Infomation and Computing Service." The point of this naming was chiefly to underscore that its design would be a rejection of the complexity of Multics, favoring a more practical and more easily developed model.
The Unix Wars
During the late 1970s and early 1980s, after the academic 'golden age' of Unix the influence it had in the classroom on young academics that were "learning by doing" led to large-scale adoption (particularly of the BSD variant) of Unix by commercial startups, most notably Sun Microsystems. Also AT&T finally decided to sit up and take notice, and this led directly to battle lines in courts being drawn, with AT&T fighting to prove that it "owned Unix."
Today
Today, in addition to certified Unix systems (see POSIX, Unix-like operating systems such as Linux, Mac OS X and BSD derivatives have matured and flourished, and many derivative works owe their ancestry to Unix roots.
Common Unix Similarities
Among the diverse array of different variations of Unix, there are general similarities that one can expect to see consistently among the different versions. Listed here are several of the "common traits" of Unix in general.
The philosophy of Unix
Although there is quite a variety among Unix systems, one common theme is the so-called "small tools that do their job very well." That is, a Unix system has many programs, each of which specializes in a small task. The user can combine these tools (via scripting or piping) to accomplish higher level goals. Although this may make some tasks more difficult than common graphical user interfaces, it allows the user to perform complicated tasks that were not explicitly allowed for by the interface's designer.
For instance, suppose the user wanted to create an archive of all files which reference his vacation created between two and three month ago. Under Unix, this could be accomplished as a combination of tar (the archiving application), find (a file search application) and grep (a file pattern matching application). In a single command:
tar czf vacation.tar.gz `find . -ctime +60 -ctime -90 -exec grep -il vacation {} \;`
In contrast, a user in a typical graphical user interface would need to use the search application to find such files, wait for the search to complete, and then use an archiving application to create the archive.
Everything is a file
In Unix everything system related is represented as a file. Special "character device files" are used to represent everything from memory, to attached devices such as mice and keyboards, to the "bit bucket". Statistics on the system are represented in a special virtual file system called /proc. For example, showing the contents (using the 'cat' command) of /dev/mouse would generate input on the screen as you moved the mouse, and specifics of the processor in use can be found in the file /proc/cpuinfo.
File Structure
One of the more influential aspects of UNIX and UNIX-like systems is their hierarchical file structure. Files are organized into directories, each of which contains further directories and files in a branching structure, with the slash character "/" used to mark directory nodes. Each directory and file in UNIX also possesses a permissions string, with nine switches which can be set to allow (r)ead, (w)rite, and e(x)ecute permissions for (u)ser, (g)roup, and (others). A directory might, for example, return the string
drwxr-xr-x 6 jsmith jsmith 204 Nov 4 11:12 directoryname
which indicates that the node is a dierctory, flagged for read, write and execute permission for its user, and read and execute only for its user's group, and others.
This combination of hierarchical structure and permissions settings enables a flexible permissions structure, that has also been included in the POSIX family of Unix standards.
User groups can be set to allow different access levels across one branch, or the entire tree, with minimal difficulty. The superuser known as "root" in UNIX automatically has access to all files and directories.
The integration of Access Control Lists, which represent an evolution in file system permissions and allows more granular permissions control, was first implemented in Sun's Solaris operating system. [2] Projects are also currently underway on several Unix variations, such as Linux[3][4] and FreeBSD.[5]
POSIX
POSIX is a standard Application Programming Interface (or API) defined by the IEEE. POSIX is usually thought of as a "Unix benchmark" today. Products that aim for Unix compliance can gain POSIX certification if they meet the requirements of the POSIX standard.[6]
Unix Today
Today Unix has a diverse and varied background, and various systems are split into branches of development, modified over time by AT&T as well as various commercial vendors and non-profit organizations (some of them drawing enough influence and inspiration from Unix that they are referred to as being Unix-like).
Copyright Owner
The present owner of the trademark UNIX® is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®" (others are called "Unix system-like" or "Unix-like"). Similarly, POSIX defines a standard set of system calls, utilities and standard library functions for Unix-like systems.