On Linux and UNIX -like systems, a program called cron1 periodically executes user-defined commands in the background. It is used for system maintenance tasks such as refreshing or removing caches, rotating and deleting old log files, and so on.
If such a command produces any output, cron typically sends an e-mail containing the output so that an admin can look at it and judge if some action is required.
But not all command-line programs are written for usage with cron. For instance, they might produce output even on successful execution, and indicate failure through a nonzero exit ...
