cat /scripts/crontab_show_all.sh

for user in $(cut -f1 -d: /etc/passwd); do echo $user; crontab -u $user -l; done

outputs a nice list like this:

in format:

user

command

root
no crontab for root
actualuser
* * * * * echo "stuff" 
bin
no crontab for bin
daemon
no crontab for daemon
adm
no crontab for adm
...
admin