UNIX is a multi-user , multi-tasking, hardware independent operating system. It is very powerful and flexible, containig over 200 utilities which allow the user to perform data management, text processing, and software develpment. UNIX runs on many machines, including micro-computers, mini-computer, and mainframe. UNIX is fast becoming the operating system of choice among third party software vendors. UNIX also has excellent communication facilities which allow users to send and receive electronic mail, transfer files, and write to each other. [ history ]

shutdown

/usr/sbin/shutdown [options]Allow a privileged user to change system state. Default behavior is to terminate user processes, taking system down from multi-user state (state 2) to single-user state. That is, only the system console provides access. Shutdown sends a warning message, waits 60 seconds, sends a final message, waits another 60 seconds, and finally prompts for confirmation. shutdown is the SVR4 alternative to halt or reboot.

Options

• -gn Use a grace-period of n seconds instead of 60.
• -ik Tell the init command to place system in state k: 0 Shutdown for safe power-off.
• -y Suppress the default prompt for confirmation.

su

su [option] [user] [shell_args] Create a shell with the effective user ID of another user (that is, login as user). If no user is specified, create a shell for a privileged user (that is, become a superuser). Enter EOF to terminate. You can run the shell with particular options by passing them as shell_args (e.g., if the shell runs sh, you can specify -c command to execute command via sh, or -r to create a restricted shell).

1969: Unix and the Net, 60's brainchildren July 7, 1999 Web posted at: 4:10 p.m. EDT (2010 GMT) by Mary Brandel (IDG) -- The 1960s ended with a bang: As it had hoped since the early 1960s, the Advanced Research Projects Agency (ARPA) saw the Arpanet -- the network that we now know as the Internet -- take shape in the last year of the decade. And at Bell Laboratories in Murray Hills, N.J., a group of computer programmers built the first version of a multiuser timesharing operating system called Unix. In time, the two events would converge, with Arpanet borrowing heavily from its birth-year twin. The Arpanet came to life in 1969 when -- with the help of Bolt Beranek and Newman Inc. in Cambridge, Mass., and teams of grad students and programmers -- the first four nodes went live at the University of California at Los Angeles, the University of California at Santa Barbara, the University of Utah in Salt Lake City and Stanford Research Institute in Stanford, Calif. The four-node network was fully operational the following year. One of the early problems to solve on the Arpanet was establishing standard commands that all participants would use. "A group of graduate students from the University of Illinois at Urbana said, 'Hey, look at Unix. This is the thing we should be using on the network,' " says Peter Salus, author of Quarter Century of Unix, (1994, Addison-Wesley Publishing Co.). For example, commands such as file transfer protocol come from Unix. Those wouldn't have been available had it not been for the work of Ken Thompson, Dennis Ritchie, Doug McIlroy and others at Bell Labs. All had been working on the Multics project, a $7 million, seven-year effort to create the first multiuser, multitasking operating system. Bell Labs withdrew from the project in 1969, and the group was disappointed about losing Multics' interactive computing environment. "There was a lot of unhappiness at the Labs," Salus explains. "So Ken and Dennis, with Doug's prodding, decided they'd try to write a system that would make them happy." Thompson wrote the operating system essentials in one month. "He set a timetable of doing one week each on the kernel, file system, editor and compiler," Salus says. "At the end of that time, he had a barely functioning system." Not named until 1970, the system would be called Unix, a play on the word Multics. Less straightforward was securing funding for further development of the operating system. After Bell Labs turned down their request for a PDP-10 computer, Thompson and Ritchie "scruffed up an unused PDP-7 that was being stored in a closet," Salus says. Unix was first implemented on that machine. The two eventually obtained a PDP-11 by promising AT&T Corp. a Unix-based text-processing application. But the turning point for Unix was in 1973 when Ritchie devised a language called C, which he used to rewrite the operating system. Because C was a high-level language, it greatly reduced the difficulty of porting Unix to different hardware platforms. It was this version of Unix that Ritchie and Thompson presented to about 200 people at the Symposium on Operating System Principles in 1973. "This was one of the first 'wow' papers," Salus says. "Almost immediately, people started calling up asking if they could get copies of this new operating system." Many characteristics made Unix attractive. It was written in a high-level language and had a hierarchical file system. It was also designed to be simple yet powerful, both in terms of the user interface and the way you could build complex programs by combining several smaller, simpler ones. "Here was an actual functioning operating system, and it worked," Salus says. More interest was generated in 1974, when Thompson and Ritchie published a paper in Communications of the ACM. About 40 organizations asked for copies of Unix during that first year, Salus says. In the next several years, many versions of Unix emerged. By 1984, about 100,000 sites were running Unix on various platforms. Today there are more than 5 million installations. "Neither Dennis nor Ken ever dreamed it would still be in use 30 years later," Salus says. Brandel is a frequent contributor to Computerworld. Contact her at brandel@cwix.com