How do I start cron on docker ubuntu base?

You can run cron without daemon mode.

root@xxxxxx:~# cron -f

I was just trying to test it:

• I started /bin/bash in a new container
• apt-get install cron nano screen
• getty tty -a root
• screen, in screen I created 2 terminals:
• first: cron -f
• second: crontab -e – edit your crontab, save and you can watch that the cron is working …