Listing All Cron Jobs
crontab -l prints the current user’s jobs. Root and system jobs live elsewhere, so check those separately to see everything scheduled on the box.
Your user jobs
crontab -l lists the crontab of the user running the command. Add nothing else for your own jobs.
Other users and root
sudo crontab -l -u www-data shows another user's jobs; sudo crontab -l shows root's.
System cron
System schedules live in /etc/crontab, /etc/cron.d/ and the /etc/cron.{hourly,daily,weekly,monthly} folders. List them to see package and OS jobs.
FAQ
How do I see all my cron jobs?
Run crontab -l to list your user jobs. Use sudo crontab -l for root and check /etc/cron.d and /etc/crontab for system jobs.
How do I list another user's cron jobs?
Use sudo crontab -l -u username to print that user’s crontab.
Where are system cron jobs stored?
In /etc/crontab, /etc/cron.d/, and the /etc/cron.hourly, .daily, .weekly and .monthly directories.