Unix was invented at Bell Labs in USA. The entire OS was written in the C language. Later, different versions of Unix evolved like SCO Unix, Digital Unix and Unix clones. The latest rage is Linux developed by Linus Trovaldt. Unix is the OS of choice in Local Area Networks & Intranets. Most web servers and ISP servers on the Internet too run on Unix or Sun 0S.
Unix is a multi-user, multi-tasking OS (i.e can perform many tasks together like Windoows) To have access to a Unix PC or server you need to have an account on that server. The account details consist of a login and a password. Only users in possession of the password can have access to the server. The server is maintained by the system administrator.
The Unix filing system is different from the DOS/Windows type. There are different levels of
file ownerships - the filing system is hierarchial or pyramidal. At the top of the pyramid
is the system administrator or root who has full authority to manage the system. At the
next level are the group ownership rights and then finally individual ownership. Every file
is owned by an individual or a group of users. The owner owns the file by virtue of
having copied it or created it himself/herself.
There are 3 types of file access permissions in Unix - read, write and execute permission.
Read permission allows read access to the file, write permission allows write access to the file i.e
modification of file and execute permission allows the person to execute the file. The owner
can set file permissions by using the chown command explained later.
Group ownership rights can be changed by the chrgp command.
Here's an example to make things clearer :
rwxr--r-- root root 10990 March 21 runme
This directory listing indicates that the file belongs to root. The first 3 characters indicate
permissions for the user (i.e file owner), the next 3 are permissions for group users and the
last 3 characters indicate permissions for others (i.e not individual/group file owners).
Take another example :
drwxr-x--- root root 10990 March 21 runme
In this example the d at the beginning indicates that it is a directory. rwx suggests that the
owner has full access permissions to the file while group ownership is limited to read and execute
access and it cannot be accessed by other users.
Unix OS is composed of a Kernel which is the core od the OS and a shell which is written in C and acrs as a link between the user and the kernel. The shell scans the input typed by the user and sends it to the kernel to be executed. There are 4 main types of shells :
Internet access is also possible in Unix. Unix offers a text-based browser Lynx. Lately, with graphical enhancements to the OS setting up Internet has become an easy task. Now, Netscape Communicator is also available fot Unix/Linux thus making for a better browsing experience.
Telnet can be used to login to a remote server from a distant location.
eg. : telnet del2.vsnl.net.in
Now you can login to a remote server if you have an account.
FTP (File Transfer Protocol) can be used similarly to download files from a remote server.
Another feature of Unix is piping i.e supplying the output (result) of one command as the input
of another.
eg: who | wc counts the number of users on the local network at the moment.
As it is a multi-tasking OS - each process has a process ID number to identify it. The ps command
shows the number of processes running concurrently along with their process ID.
eg: ps
bash 119
x windows 120
The kill command terminates a current process. eg: kill 120
| Command Syntax | What it does |
| rm filename | delete file |
| cp filename destination | copy file |
| ls filename | Display file |
| cat filename | Displays file contents |
| who | Displays online users |
| passwd | change your password |
| wc filename | Counts words, characters, lines in the file and displays stats |
| mv filename newname | rename filename |
| cd filename | change directory |
| mkdir dirname | make directory |
| rmdir dirname | remove directory |
| pwd | displays present working directory |