Directing input and output

General information about processes

Programs and commands running on a workstation are called processes (and sometimes tasks or jobs). You can have several processes running at the same time, but you can interact with only one of them at a time. It's a bit like switching channels on a television. You can watch only one station at any given moment, but all the other stations are still broadcasting.

Every time you enter a command, start a program or open a new window, you start a new process. Although only one process can be in the foreground at any given moment, you can have several background processes running simultaneously. Background processes simply do their work out of your way, allowing you to focus on tasks that really do need your attention.

Please note that some processes are automatically placed in the background. For instance, programs selected from the root application menu.

Also realize that sometimes programs and commands don't always start as quickly as you might like. If you issue a command or start a program and nothing seems to happen, wait a while (perhaps an entire minute) before trying again. If you impatiently try to start a program five times you might just end up with five copies of the program running on your machine, a sure way to make your workstation slow down.

Unix usually reads input from the keyboard and displays output on the computer screen. However, you can redirect the input and output of commands to suit your needs, connecting commands to use the output of one command as the input of another (called piping) or running several different processes or programs quietly in the background while you do something else entirely.

Basics of directing input and output

• Moving processes around (fg/bg)
  
• Listing your processes (ps/jobs)
  
• Suspending processes
  
• Killing processes (kill)
  
• Redirecting commands (<>)
  
• Combining commands (piping).

Last modified November 23, 2004 by cawalker