Читать книгу Linux Bible - Christopher Negus - Страница 182

If you have programs that you want to run while you continue to work in the shell, you can place the programs in the background. To place a program in the background at the time you run the program, type an ampersand (&) at the end of the command line, like this:

 $ find /usr> /tmp/allusrfiles & [3] 15971

This example command finds all files on your Linux system (starting from /usr), prints those filenames, and puts those names in the file /tmp/allusrfiles. The ampersand (&) runs that command line in the background. Notice that the job number, [3], and process ID number, 15971, are displayed when the command is launched. To check which commands you have running in the background, use the jobs command, as follows:

 $ jobs [1] Stopped (tty output) vi /tmp/myfile [2] Running find /usr -print > /tmp/allusrfiles & [3] Running nroff -man /usr/man2/* >/tmp/man2 & [4]- Running nroff -man /usr/man3/* >/tmp/man3 & [5]+ Stopped nroff -man /usr/man4/* >/tmp/man4

The first job shows a text-editing command (vi) that I placed in the background and stopped by pressing Ctrl+Z while I was editing. Job 2 shows the find command I just ran. Jobs 3 and 4 show nroff commands currently running in the background. Job 5 had been running in the shell (foreground) until I decided too many processes were running and pressed Ctrl+Z to stop job 5 until a few processes had completed.

The plus sign (+) next to number 5 shows that it was most recently placed in the background. The minus sign (-) next to number 4 shows that it was placed in the background just before the most recent background job. Because job 1 requires terminal input, it cannot run in the background. As a result, it is Stopped until it is brought to the foreground again.