RHEL or CentOS users have two repositories to choose from: the well-known Extra Packages for Enterprise Linux (EPEL) and the Zabbix repository. EPEL might be a safer choice, but it might not always have the latest version. (In fact, at the time of writing, the latest version in EPEL was still 3.0.22, so it's possible that 4.0 will not be available in EPEL). In production, most of the time you will encounter setups with Security-Enhanced Linux (SELinux) enabled. However, SELinux is rather complex on its own, so it's out of the scope of this book; please disable SELinux before you start with the installation of Zabbix. If you have no clue how to do so, this can be done by editing the /etc/selinux/config file and putting disable or permissive instead of enabled. Don't forget to reboot afterwards so that changes are applied to the system. You can verify the status with the getenforce command.