It’s assumed you already have a server with a base CentOS installation before you begin.  Do NOT install a GUI such as Gnome or KDE.  We only want to be running in console text mode not GUI graphics mode.  If you already have a desktop or server GUI installed you will want to exit to console mode.  You do that by typing init 3 from a terminal or console window.  You will need to be logged in as root in order to do this so if not you can su root.  All instructions in this guide are assuming you are always logged in as root running in level 3 console text mode.

Via OpenSIPS and Control Panel Install Guide | PowerPBX.org.