Red Hat journalctl

Reference - https://www.loggly.com/ultimate-guide/using-journalctl/
journalctl -b
journalctl -b -1
journalctl --list-boots
journalctl --since "1 hour ago"
journalctl --since "2 days ago"
journalctl --since "2015-06-26 23:15:00" --until "2015-06-26 23:20:00"
journalctl -u nginx.service
journalctl -u nginx.service -u mysql.service
journalctl -f
journalctl -u mysql.service -f
journalctl -n 50 --since "1 hour ago"
journalctl -u sshd.service -r -n 1