Basic Concepts
Learning the prime function and uses of the Linux system
A Graphical User Interface (GUI) utilizes graphic elements such as icons and object-like representation of the computer and constituent applications. The user interacts with the interface by selecting and executing items with the mouse. Central to a command line interface (CLI) is a prompt at which the user types commands that are interpreted by the OS and then executed. Users type specific commands to move to other directories, copy files, execute programs and so on. The Linux OS provides a powerful CLI. X Windows provides GUI functionality to a system running the Linux OS. However, in the same way that an MS DOS command window may be initiated from the Windows GUI, an 'xterm' may be initiated from X Windows to provide a CLI interface.
The Linux command line runs on a shell that interfaces between the user and the Operating System. The shell reads commands from the keyboard, processes them, and sends them to the operating system. Bash (Bourne Again SHell) is the default shell on most Linux systems. A terminal emulator is a program that is part of Linux GUIs like X-Windows. The terminal emulator opens up a window and runs a shell in the window. Examples of terminal emulators for X Windows include xterm, gnome-terminal, konsole, rxvt, and so on.
While a terminal emulator opens a new shell within a GUI, working on a virtual terminal is similar to working on the console of the OS itself - the console is the main shell that starts and shuts down even the GUI. Shutting down the GUI will take a user to the console; the virtual terminal just allows a user to switch back and forth between the GUI and the CLI of the OS. Linux typically runs six virtual terminals; X-Windows runs off the seventh virtual terminal. The user may access the first virtual terminal by pressing Ctrl+Alt+F1, second virtual terminal by pressing Ctrl+Alt+F2 and so on. Ctrl+Alt+F7 switches back to the GUI. A user may login at a virtual terminal by entering the appropriate user name and password.
The Linux OS performs two basic functions: Multitasking or switching back and forth between tasks to achieve seamless execution of all tasks and multi-user support and tracking - monitoring the actions of each user's programs and tasks, assigning priorities, permissions, and resources.
