The ubuntu operating system

Ubuntu is an operating system. To understand what the words kernel, shell and X mean we need to understand operating systems a bit more.

There is only one real computer, and that's the hardware. On its own this can do nothing. To make it useful you need to give it instructions called software. You can think of software as being in layers around the hardware but unless you are a computer scientist its hard to imagine. Its a bit like an onion, about which more later. Meanwhile let's use the analogy of the human body.

The body is made up of bone, muscle, fat, nerves and specialised organs. A computer is made of a motherboard, processors, a power supply, wires and peripherals like drives, keyboards, printers and screens.

The body is made to work by the nervous system. This sends instructions to, and gathers information from, the bits that make up the body. There is a part that is autonomous, that works all on its own. Its speeds up our heart and breathing when we run, and makes us draw our hand away when we burn it. It also watches out for us to decide to do something like moving a limb or speaking. In computers this is software called the kernel. It knows how to operate a printer, drive, keyboard and so on and how to connect to other computers.

The nervous system allows us to use tools like a chef's knife. It works out what needs to be done and instructs muscles to do it. We decide what's to be done and the brain and nervous system controls it. In computers this is the user interface or shell. We can tell it to print a document or save a file on a disk.

Sticking to cooking, we can carry out a task like cooking a curry by following a recipe. This has a series of instructions, for example 'chop the onions finely and fry in oil until soft'. We read the instructions and the nervous system enables us to carry them out and flushes our eyes with liquid to stop the stinging. In computing these sets of instructions are called programs or applications.

If a friend phones you to ask for the recipe you can post it, email it as an attachment or read it to him or her. For a computer this means sending data to other computers either directly over a network or the Internet, or indirectly by sharing using a disk or memory stick.

So a computer has layers like an onion:

Computer Body
Real computer Bone, muscle, fat, nerves and organs
Kernel Autonomic nervous system
User interface (shell and X) Nervous system and muscles using tools
Application Recipe
Communication Post, email, voice


The operating system is the kernel and shell.

The kernel is linux.

The shell contains a set of commands that can be typed in by a user. There is a pale imitation of this in the later-developed Windows operating system, called the command prompt.

X window (Unity in ubuntu) is the graphical interface.


There is a special user privilege in linux called 'super-user'. This God-like creature can do anything, anywhere on the system CAREFULLY. Shell commands are very powerful. Some can only be used by someone logged in as super-user. Linux administrators will log in as super-user only for brief periods whilst using dangerous commands then return to their usual user status. It is possible to run single super-user commands by starting the line with the word sudo.

For example:

peter@zoostorm:~$ sudo fdisk -l

This will list the storage areas (partitions) on a hard disk


(C) Peter Scott 2013

Last edit 26 December 2016