How do I view currently setup or all running cron jobs under Linux operating systems?

The cron service searches its spool area (usually /var/spool/cron/crontabs) for crontab files (which are named after user accounts); crontabs found are loaded into memory. cron also reads /etc/crontab, which is in a slightly different format. Additionally, cron reads the files in /etc/cron.d: it treats the files in /etc/cron.d as in the same way as the /etc/crontab file. The intended purpose of /etc/cron.d/ directory feature is to allow packages that require finer control of their scheduling than the /etc/cron.{daily,weekly,monthly} directories to add a crontab file to /etc/cron.d.View Users Cronjob

Use the following syntax to view username users cronjob:

crontab -u userName -l
crontab -u username -l

View Root User Cronjob

Just type the following command:

crontab -l

View /etc/crontab

A cronjob can be also run from /etc/crontab file. To view it, enter:

# less /etc/crontab

View Daily Cronjob

Type the following commands:

cd /etc/cron.daily/
ls -l
cat filename

View Hourly Cronjobs

Type the following commands:

cd /etc/cron.hourly/
ls -l
cat filename

View Weekly Cronjobs

Type the following commands:

cd /etc/cron.weekly/
ls -l
cat filename

View Monthly Cronjobs

Type the following commands:

cd /etc/cron.monthly/
ls -l
cat filename

View Software (Package) Specific Cronjobs

Type the following commands

cd /etc/cron.d/
ls -l
cat filename