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Job control

Job control can best be illustrated with an example. Enter the following to start and stop three jobs and list them:

info bash
Ctrl+Z
info ls
Ctrl+Z
info
Ctrl+Z
jobs

...to display:

Each job (process running in a particular shell) is allocated a job number. The plus (+) sign indicates the most recent job and the minus (-) sign indicates the job before that. Now enter:

fg %1

...to bring job number 1 back to the foreground, then press Ctrl+Z to stop it again, and enter:

jobs

...to list the jobs again:

Notice how the most recent (+) and previous (-) job, has changed.

With the info program you can just bring each job to the foreground and press q to quit. (By default fg on its own brings the most recent job to the foreground.) Do this now to end each of the three jobs.

Background jobs

Some things you type at the command-line can take a long time to complete, for instance, enter:

tree -d /usr > usrdirs.txt

...to redirect (>) a tree depiction (tree) of the directories (-d) in the massive /usr directory, to the file usrdirs.txt.

Now whilst that's going on, press Ctrl+Z to stop it, and enter:

bg

...to run the most recent job (the tree command) in the background, allowing you to continue with other things in the meantime. (As with fg, you can enter say bg %2, to run job number 2 in the background.)

Better than the above, is to enter the command, followed by an ampersand (&) to tell the shell to run the command in the background:

tree -d /usr > usrdirs.txt &

This you'll often do in a terminal window, to launch an X program, and allow you to continue typing away. For example:

netscape &

...will run the Netscape Navigator Web browser in the background, displaying in the terminal window the job number and PID (process ID) given to the job.

Permanently stopping jobs

To permanently stop the most recent background/stopped job, you could enter:

kill %

...or to specify the particular background/stopped job, enter:

kill %2

Much of the time Ctrl+C will also permantely stop a job running in the foreground, and the most recent background job can also be stopped with:

fg
Ctrl+C

Note:

Sometimes when you press Ctrl+D to logout you'll receive a message saying there are stopped jobs. Here a second press of Ctrl+D will ignore this warning.

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