Anacron - a computer program that performs periodic command scheduling
anacron - cron job without assuming that the system is running continuously
Anacron makes sure that all the tasks listed in /etc/cron.hourly , /etc/cron.daily , /etc/cron.weekly and /etc/cron.monthly are performed, even if the PC is switched off when they'd normally happen. Overdue tasks are run when the computer is next turned on. On the good side, it never misses a task. On the bad side, if the tasks take a lot of time, your PC might seem a little slow when you first turn it on after a long time being turned off.
To make cron-apt be executed by Anacron, create a link in etc/cron.hourly , /etc/cron.daily , /etc/cron.weekly or /etc/cron.monthly. For example:
sudo ln -s /usr/sbin/cron-apt /etc/cron.weekly/