Learning Unix for OS X

Chapter 7. Multitasking

OS X can do many jobs at once, dividing the processor’s time between running applications and system processes so quickly that it looks as if everything is running at the same time. This is called multitasking. As new applications are launched, processes are started, and others go idle or shut down entirely, the system monitors each of these tasks and doles out memory and CPU resources on the fly to make sure everything runs smoothly.

Most users think of multitasking in terms of the way OS X handles applications like Adobe Photoshop, Microsoft Word, Mail, iChat, Safari, etc.—allowing you to have multiple applications open, each with its own windows. But on the Unix side, OS X allows you to run multiple Unix programs and/or processes at the same time as well. These processes can all be run and monitored through one single Terminal window, with a little help from something called job control. 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 having multiple Terminal windows open when you really don’t need to.

Why else would you want job control? Suppose you’re running a Unix program that takes a long time to run. On a single-task operating system, you would enter the command and wait for the job to finish, returning you to the command prompt (which is your indication that you’re free to enter a new ...