Linux Security: https://linuxsecurity.com/ The official VirtualBox website: https://www.virtualbox.org/ The Ubuntu "Alternate Installer" download page: https://ubuntu.com/download/alternative-downloads#alternate-ubuntu-server-installer The official CentOS page: https://www.centos.org/ RHEL documentation (this also works for CentOS): https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/ How to Set Up Automatic Updates on Ubuntu Server 18.04: https://libre-software.net/ubuntu-automatic-updates/ Enabling Automatic Updates in RHEL 7 and CentOS 7: https://linuxaria.com/howto/enabling-automatic-updates-in-centos-7-and-rhel-7 Managing and Monitoring Security Updates for RHEL 8: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/managing_and_monitoring_security_updates/index ...