Commands and Processes

A command is a request to perform an operation or run a program. You use commands to tell the operating system what task you want it to perform. When commands are entered, they are deciphered by a command interpreter (also known as a shell) and that task is processed.

A program or command that is actually running on the computer is referred to as a process. The operating system can run many different processes at the same time.

The operating system allows you to manipulate the input and output (I/O) of data to and from your system by using specific I/O commands and symbols. You can control input by specifying the location from which to gather data. For example, you can specify to read input while data is entered on the keyboard (standard input) or to read input from a file. You can control output by specifying where to display or store data. For example, you can specify to write output data to the screen (standard output) or to write it to a file.

This chapter discusses the following:

• Commands Overview
  • Command Syntax
  • Reading Usage Statements
  • Using Web-based System Manager
  • Using the smit Command
  • Locating a Command or Program (whereis Command)
  • Displaying Information about a Command (man Command)
  • Displaying the Function of a Command (whatis Command)
  • Listing Previously Entered Commands (history Shell Command)
  • Repeating Commands Using the history Shell Command
  • Substituting Strings Using the history Shell Command
  • Editing the Command History
  • Creating a Command Alias (alias Shell Command)
  • Working with Text-Formatting Commands
• Processes Overview
  • Foreground and Background Processes
  • Daemons
  • Zombie Process
  • Starting a Process
  • Checking Processes (ps Command)
  • Setting the Initial Priority of a Process (nice Command)
  • Changing the Priority of a Running Process (renice Command)
  • Canceling a Foreground Process
  • Stopping a Foreground Process
  • Restarting a Stopped Process
  • Scheduling a Process for Later Operation (at Command)
  • Listing All Scheduled Processes (at or atq Command)
  • Removing a Process from the Schedule (at Command)
  • Removing a Background Process (kill Command)
• Command Summary for Commands and Processes