When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter CLI. It interprets the commands the user types in and arranges for them to be carried out. Staff and students in the school have the tcsh shell by default. Filename Completion - By typing part of the name of a command, filename or directory and pressing the [ Tab ] key, the tcsh shell will complete the rest of the name automatically.
If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again. History - The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.
A file is a collection of data. They are created by users using text editors, running compilers etc. From within a windowing session at the machine itself, select the logout option from your root menu see the section on the windowing system for more details , and then confirm the logout by clicking on yes. If you leave yourself logged on then other people may come along and use your account, access your email etc.
Whilst in a University environment this is not necessarily a problem - the next user will probably come along and log you out so that they can log on themselves it is important to log out so that other people don't waste time wondering whether you have finished, or have just popped out for a few minutes.
Don't lock your workstation - this is anti-social behaviour as it prevents anyone else using it, and if we see it we'll log you out anyway, and probably take all your pocket money away. If you leave for more than a few minutes, log yourself out. One of the advantages of a UNIX system is that you can leave a job running in the 'background' don't worry, we'll get to that later which means it'll keep running for as long as you want even after you log out.
All information in UNIX, whether it is a program, data or text, is stored in files. These files are maintained by the operating system on hard disks usually , and read into the computer's memory when required. In fact, directories are really a special kind of file, but the user perceives the whole structure as forming a hierarchy of files and directories. This hierarchy is known as the filesystem.
When UNIX computers are networked, the filesystem is not contained within one single machine, but spans the entire network. Each file and directory within the network filesystem is addressable via its own unique name - its filename , or directory name , and to the user the fact that the filesystem straddles multiple machines and hard disks goes largely unnoticed.
The filesystem may be visualised as the roots of a tree see Fig. Beneath this directory lie the other directories containing files and further directories, including data and references to data stored elsewhere on the network. We have already mentioned that every file or directory in the filesystem is uniquely addressable by its filename or directory name.
In fact a file's full name is a description of the path from the root of the file system to the file itself. For instance, the directory bin under the usr directory has the full name:.
A directory contained within another directory is known as a sub-directory of its parent , or container, directory. With this nomenclature we are able to move around the filesystem. Similarly, relative pathnames are permissible, describing the route to another path or directory from the current directory: the sub-directory recipes in the mdisney directory may be addressed either absolutely as:.
An analogy is the address of your next door neighbour's house. If you wanted to tell a friend what next door's address is, you could give them the house number, the street, the city, the post code, and even the country.
That's the absolute path name to your neighbour's house. Of course it's much easier to specify "one house up from mine" or "number 18" etc. This is the relative path relative to yours.
Each user in a UNIX network system has specific area of the filesystem belonging to them known as their home directory in which they are initially placed when they log on. Armed with a basic knowledge of the structure of the filesystem, each user is free to explore and visit almost any area of the system unless it has been specifically protected by its owner. To move around the filesystem the command cd , for c hange d irectory is generally used. From this directory, to get to the home directory we would type either.
Usually the path with the least typing involved is chosen! The command ls , for list, is used to examine the contents of a directory e. You may have noticed from these examples that unlike some other operating systems, UNIX does not in general tell you when it has completed a command, it simply prints another prompt. One other useful directory name is. This is very useful, especially when performing operations such as copying files from "somewhere else" to "here":. We'll deal with cp , for copy, in more details later.
Users communicate with the kernel through a program known as the shell. The shell is a command line interpreter; it translates commands entered by the user and converts them into a language that is understood by the kernel.
There are various Unix variants available in the market. Linux is also a flavor of Unix which is freely available. Several people can use a Unix computer at the same time; hence Unix is called a multiuser system. A user can also run multiple programs at the same time; hence Unix is a multitasking environment. It interacts with the hardware and most of the tasks like memory management, task scheduling and file management.
When you type in a command at your terminal, the shell interprets the command and calls the program that you want. The shell uses standard syntax for all commands. There are over standard commands plus numerous others provided through 3 rd party software. All the commands come along with various options. All files are then organized into directories. These directories are further organized into a tree-like structure called the filesystem.
If you have a computer which has the Unix operating system installed in it, then you simply need to turn on the system to make it live. As soon as you turn on the system, it starts booting up and finally it prompts you to log into the system, which is an activity to log into the system and use it for your day-to-day activities. Have your userid user identification and password ready.
Contact your system administrator if you don't have these yet.
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