The graphical user interface (or GUI) used by most Linux systems is built on top of an implementation of the X Window System. More recently, the Linux community seeks to advance to Wayland as the new display server protocol in place of X11. Many other open-source software projects contribute to Linux systems.

Is Linux a GUI or CUI?

An operating system like UNIX has CLI, While an operating system like Linux and windows have both CLI and GUI.

Why is Cui better than GUI?

A GUI can display graphics, symbols and other visual cues as opposed to strictly text, unlike the CUI. GUIs are much easier to navigate, as they make the use of a mouse possible. Therefore GUI is more popular than CUI.