TAILIEUCHUNG - Multitasking

With a window system, you can have many applications running at the same time, with many windows open. But most Unix systems also let you run more than one program inside the same terminal. This is called job contr ol. It gives some of the benefits of window systems to users who don’t have windows. But, even if you’re using a window system, you may want to use job control to do several things inside the same terminal window. For instance, you may prefer to do most of your work from one terminal window, instead of covering your desktop with multiple windows | 7 Multitasking In this chapter Running a Command in the Background Checking on a Process Cancelling a Process Unix can do many jobs at once dividing the processor s time between the tasks so quickly that it looks as if everything is running at the same time. This is called multitasking. With a window system you can have many applications running at the same time with many windows open. But most Unix systems also let you run more than one program inside the same terminal. This is called job control. It gives some of the benefits of window systems to users who don t have windows. But even if you re using a window system you may want to use job control to do several things inside the same terminal window. For instance you may prefer to do most of your work from one terminal window instead of covering your desktop with multiple windows. Why else would you want job control Suppose you re running a program that will take a long time to process. On a single-task operating system such as MS-DOS you would enter the command and wait for the system prompt to return telling you that you could enter a new command. In Unix however you can enter new commands in the foreground while one or more programs are still running in the background. When you enter a command as a background process the shell prompt reappears immediately so that you can enter a new command. The original program will still run in the background but you can use the system to do other things during that time. Depending on your system and your shell you may even be able to log off and let the background process run to completion. 130 7 January 2002 13 14 Running a Command in the Background 131 Running a Command in the Background Running a program as a background process is most often done to free a terminal when you know the program will take a long time to run. It s used whenever you want to launch a new window program from an existing terminal window so that you can keep working in the existing terminal as well

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