Explain different layers of UNIX operating system Also explain interaction between shell and kernel using any suitable command?

Answer 1

Layers of UNIX Operation System along with an example to illustrate the interaction between shell and Kernel.

The UNIX operating system is made up of three parts: the kernel, the shell and the programs.

The kernel

The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls.

The shell

The shell acts as an interface between the user and the kernel. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt ($ on our systems).

The programs

A program is refereed to as a process while the kernel is running it. The Kernel can run the same shell program(or any other program) simultaneously for many users on a Unix System, and each running copy of the program is a separate process. The Shell is also a program that the UNIX Kernel runs for the user.

As an illustration of the way that the shell and the kernel work together, suppose a user types rm myfile(which has the effect of removing the file myfile). The shell searches the filestore for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on myfile. When the process rm myfile has finished running, the shell then returns the UNIX prompt $ to the user, indicating that it is waiting for further commands.

- Submitted by SRK

Student of NIIT

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