Scheduling of tasks under Linux is an extremely powerful procedure that is used by almost everyone. Scheduling of tasks basically means running whichever program you want at a particular time without having to manually be present at the machine at that time. Linux will run that program for you at that time. In this article I shall explain the simplest way to schedule tasks using the simple command called ‘at.’
Advanced task scheduling is possible using ‘cron.’ Use ‘cron’ if you want to repeatedly execute any task.
At the prompt, type this command followed by Enter:
$ at 2359
The moment you press Enter, the prompt changes into an arrow indicating that more information is required by Linux. Type the following command assuming you have installed XMMS player, which plays mp3 files, and that you actually have an mp3 file in the directory shown below
> xmms /home/david/mp3s/rock_my_world.mp3
Once you have typed the above, press <Enter> and then finally press <Ctrl>-D
That’s it. Now Linux will make the XMMS player play the particular mp3 file at the time 23:59. Thats just a minute before midnight. Linux surely rocks your world!
Basically, if you are using the 24-hour clock, then you enter the time you want with the hours and the minutes together one after another. Hours = 0-23 and Minutes = 0-59. Then type the exact command that you would have typed had you wanted to execute the task manually. If you want, you can issue more commands after the first one. Once you finish entering all the tasks, press <Ctrl>-D to indicate that you have finished. Then wait and enjoy. Linux will do the rest.
At any time, you can see the list of pending jobs by typing the following at the prompt:
$ at -l (that’s a lowercase ‘L’)
If you want to remove any particular job in case you suddenly decide that you don’t want that program to execute, then first get the list of pending jobs as shown above. You will see that every job has a corresponding ID associated with it. Use the command below (In this case to remove job with ID=10)
$ atrm 10