Process startup

You start a foreground process from a display station by either entering a program name or command name at the system prompt.

After a foreground process has started, the process interacts with you at your display station until it is complete. No other interaction (for example, entering another command) can take place at the display station until the process is finished or you halt it.

A single user can run more than one process at a time, up to a default maximum of 40 processes per user.

Starting a process in the foreground

To start a process in the foreground, enter the name of the command with the appropriate parameters and flags:

$ CommandName

Starting a process in the background

To run a process in the background, type the name of the command with the appropriate parameters and flags, followed by an ampersand (&):

$ CommandName&

When a process is running in the background, you can perform additional tasks by entering other commands at your display station.

Generally, background processes are most useful for commands that take a long time to run. However, because they increase the total amount of work the processor is doing, background processes can slow down the rest of the system.

Most processes direct their output to standard output, even when they run in the background. Unless redirected, standard output goes to the display device. Because the output from a background process can interfere with your other work on the system, it is usually good practice to redirect the output of a background process to a file or a printer. You can then look at the output whenever you are ready.

Note: Under certain circumstances, a process might generate its output in a different sequence when run in the background than when run in the foreground. Programmers might want to use the fflush subroutine to ensure that output occurs in the correct order regardless of whether the process runs in foreground or background.

While a background process is running, you can check its status with the ps command.