UNIX is an operating system consisting of three important features; a kernel, the shell and a file system.
As its name implies, the kernel is at the core of each UNIX system and is loaded in whenever the system is started up - referred to as a boot of the system. It manages the entire resources of the system, presenting them to you and every other user as a coherent system. You do not need to know anything about the kernel in order to use a UNIX system. Amongst the functions performed by the kernel are:
Whenever you login to a Unix system you are placed in a program called the shell. You can see its prompt at the bottom left of your screen. To get your work done, you enter commands at this prompt. The shell acts as a command interpreter; it takes each command and passes it to the operating system kernel to be acted upon. It then displays the results of this operation on your screen. The shell provides you with one or more of the following features. You can:
A file system is a logical method for organizing and storing large amounts of information in a way which makes it easy manage. The file system is the smallest unit in which information is stored. The UNIX file system has several important features:
To you, the user, it appears as though there is only one type of file in UNIX - the file which is used to hold your information. In fact, the UNIX file system contains several types of files.
Having your own directory structure gives you a definable place to work from and allows you to structure your information in a way that makes best sense to you.
Directories which you create belong to you - you are said to "own" them - and you can set access permissions to control which other users can have access to the information they contain.
It may seem unusual to think of a physical device as a file, but it allows you to send the output of a command to a device in the same way that you send it to a file. For example:
cat scream.au > /dev/audio
This sends the contents of the sound file scream.au to the file /dev/audio which represents the audio device attached to the system. Guess what sound this makes?
The directory /dev contains the special files which are used to represent devices on a UNIX system.
User's home directories are usually grouped together under a system directory such as /home. A large UNIX system may have several hundred users, with their home directories grouped in sub directories according to some schema such as their organizational department.
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