For Scheduling a Single Job: at

The at command allows you to schedule a job for execution at a later time. The job can consist of a single command or a script.

Similar to crontab, the at command allows you to schedule the automatic execution of routine tasks. However, unlike crontab files, at files execute their tasks once, and then are removed from their directory. Therefore, at is most useful for running simple commands or scripts that direct output into separate files for later examination.

Submitting an at job involves entering a command and following the at command syntax to specify options to schedule the time your job will be executed. For more information about submitting at jobs, see Description of the at Command.

The at command stores the command or script you entered, along with a copy of your current environment variable in the /var/spool/cron/atjobs directory. Your at job file name is given a long number that specifies its location in the at queue, followed by the .a extension, such as 793962000.a.

The cron daemon periodically executes the atrun program, usually at 15-minute intervals. Then the atrun program executes at jobs at their scheduled times. After the cron daemon executes your at job, the at job's file is removed from the atjobs directory.

For step-by-step instructions on scheduling at jobs, see How to Create an at Job.