Unix and Shell programming

The good old dumb terminal connected to the computer's serial port was once the only means of connecting to a UNIX system. Later, the TELNET program became popular for connecting in a network.  For security reasons, the TELNET facility could be disabled on your system and the SECURE SHELL( SSH ) could be the only means of connecting to a remote UNIX box. In that case, UNIX and LINUX users can use the SSH command if available. Windows users may use PUTTY or any of the free SSH programs available on the Net. If you are using a workstation or desktop PC running Linux, then you can log in directly.

On a large system serving hundreds of users, someone has to be given charge of administration of the system.  This person is known as the system administrator . The administrator is responsible for the management of the entire setup. She allocates user accounts, maintains file systems, takes backups,manages disk space and performs several other important functions. She is the person to be contacted in case of a genuine problem. If you own a workstation or PC that runs some flavor of UNIX, then you are probably its administrator . You are then directly responsible for its startup, shutdown and maintenance. If you lose a file, it's your job to get it from a backup. If things don't work properly, you have to try all possible means to set them right before you decide to call a maintenance person. You can use a UNIX machine only after the administrator has opened an account with a user-id and password for your use. These authentication parameters are maintained in two separate files...

Unlike Windows, UNIX can be used by several users concurrently. In Other words, a single copy of the operating system software installed on just one machine can serve the needs of hundreds of users. These users could use dumb terminals or their own desktop PCs to access a central UNIX computer. This computer will probably be located in a separate room with restricted access. If you are using a PC, then it must be configured properly before it can be used to connect to a  UNIX system.  Things are quite different, however, when you are using a WORKSTATION . This is a computer capable of producing high-quality graphics but meant to be used by a single user. Unlike the dumb terminal, a workstation has its own CPU , memory( the RAM--random access memory ), hard disk , CD-ROM , mouse as a pointing device, and printer . Since it has all the things that UNIX needs, a workstation can run its own UNIX. Desktop PCs are also often referred to as workstations because there are...

There have been many operating systems in the past, one at least from each hardware vendor. They were written in a near-machine language known as ASSEMBLER. The systems were proprietary( relating to an owner or ownership or  (of a product) marketed under and protected by a registered trade name .)  because assembler code developed on one machine wouldn't run on another. Vendors required consumers to purchase expensive proprietary hardware and software if two dissimilar machines needed to talk to each other. Ken Thompson and Dennis Ritchie changed all that forever. They created UNIX . This UNIX operating system marks a strong departure from tradition.It has practically everything an operating system should have, but also introduced a number of concepts previously unknown to the computing community. Beginners with some experience in Windows think of UNIX in terms of it, quite oblivious to the fact that the similarities are only superficial. UNIX is way ahead of othe...

1.1 The Operating system Computers re designed to run programs. But a program can run only if the computer it is running on has some basic intelligence to begin with  . This intelligence allocates memory for the program runs each program instruction on the CPU and accesses the hardware on behalf of the program. A special piece of pre-installed software performs this job, and this software is known as the computer's operating system. An Operating system is the software that manages the computer's  hardware and provides a convenient and safe environment  for running programs. It acts as an interface between programs and the hardware resources that these programs access(like memory, hard disk and printer). It is loaded into memory when a computer  is booted and remains active as the machine is up. To grasp the key features of an operating system, Let 's consider the management tasks it has to perform when we run a program.  These operations also ...