FreeBSD® Unleashed

Creating Jobs to Run One Time with the at Command

Okay, so cron is amazingly useful for regularly scheduled tasks. However, what about a task that you only want to happen once—something you want to postpone until some later time when you won't be around to execute it yourself? You could do this with cron, setting up a crontab file to have an entry that runs crontab -u at the end to delete itself. However, there is a better way: the at program.

at is actually made up of several commands: at (the job creator), atq (which displays pending jobs), and atrm (which lets you cancel pending jobs listed in atq). There is also a batch command, which is a version of at that will run only if the system load is less than some value (1.5 is the compiled-in ...