uses the /etc/crontab file

if the system is not available anacron checks to see that was missed and will run it.

you also have the /etc/cron.daily /etc/cron/weekly and /etc/cron/monthly

you can place executable files on those directories and they will be executed. You do not have control of the exact time when its done

At system boot, one of the first systemd service units to launch is the systemd-tmpfiles-setup service. This service runs the systemd-tmpfiles command –create –remove option, which reads instructions from the /usr/lib/tmpfiles.d/*.conf, /run/tmpfiles.d/*.conf, and /etc/tmpfiles.d/*.conf configuration files. These configuration files list files and directories that the systemd-tmpfiles-setup service is instructed to create, delete, or secure with permissions.

To prevent long-running systems from filling up their disks with stale data, a systemd timer unit called systemd-tmpfiles-clean.timer triggers at a regular interval the systemd-tmpfiles-clean.service unit, which executes the systemd-tmpfiles –clean command.