Identity

Daemon: cron (Debian/Ubuntu) or crond (RHEL/Fedora/Arch)
Unit: cron.service (Debian/Ubuntu) or crond.service (RHEL/Fedora)
User crontabs: crontab -e — stored in /var/spool/cron/crontabs/<user>
System crontab: /etc/crontab — includes a username field; read by cron directly
Drop-in dir: /etc/cron.d/ — same syntax as /etc/crontab (username field required)
Run-parts dirs: /etc/cron.hourly/, /etc/cron.daily/, /etc/cron.weekly/, /etc/cron.monthly/
Logs: journalctl -u cron or journalctl -u crond; also /var/log/syslog (Debian) or /var/log/cron (RHEL)
Distro install: apt install cron / dnf install cronie

Key Operations

Operation	Command
List current user's crontab	`crontab -l`
Edit current user's crontab	`crontab -e`
Edit another user's crontab (root)	`crontab -u username -e`
List another user's crontab (root)	`crontab -u username -l`
Remove current user's crontab	`crontab -r`