See all the user's crontab task - mlzhu007 column - CSDN blog
https://blog.csdn.net/mlzhu007/article/details/81662091
The root user
cat /etc/passwd | cut -f 1 -d : |xargs -I {} crontab -l -u {}
Linux crontab command | newbie tutorial
https://www.runoob.com/linux/linux-comm-crontab.html
View crontab linux implementation of the mandate - youzhouliu's blog - CSDN blog
https://blog.csdn.net/youzhouliu/article/details/54311099
View a user's crontab task
crontab -l -u username