anacron is a computer program that performs periodic command scheduling, which is traditionally done by cron, but without assuming that the system is running continuously.

anacron was originally conceived and implemented by Christian Schwarz in Perl, for the Unix operating system.

Upon starting, this command can then automatically request to run itself at a future date, thus giving the appearance of a regularly scheduled task, with guaranteed execution.

This behaviour can be overridden to allow concurrent (parallel) tasks, but can consume system resources that are needed by the user to do work.

In contrast, cron will only run daily tasks at the time set (e.g. in the middle of the night, when presumably the machine is not being used).