Simple concept. We want to ensure that our Pi is available and reliable.
It is inevitable that networks get hickups, or the Pi runs out of memory requiring restart at a regular interval.
For exaomple if you want to run a bash file after a reboot every 6am and 6pm, you would setup a crontab as follows:
sudo crontab -e
#M H D M DW CMD
0 6,18 * * * /sbin/shutdown -r
@reboot cd /home/pi && sh notify.sh
You could also run a python 3 program as a root every first day of each month, as such:
sudo crontab -e
#M H D M DW CMD
0 0 1 * * root /usr/bin/python3 /home/pi/hello.py
The linux crontab format:
MIN HOUR DOM MON DOW CMD
MIN minute 0-59
HOUR hour 0-23
DOM day of month 1-31
MON month 1-12
DOW day of week 0-6
CMD command Command script to be executed
Good luck!