Principles of operating systems, Operating System

Assignment Help:

Objective - Tiny Shell (tish)

In this exercise you will write a small shell program to run different programs in foreground and background mode.

Background

Usually when you login on to the system the program that takes control and takes care of your requests is the "shell" program. In this exercise you will implement only a small portion of the shell capabilities.

Assignment

Your assignment is to build a program "tish" that will implement the following shell services:

  • Run programs in foreground and background;
  • List all processes that currently run in the background.
  • Kill a process running in the background.

The precise requirements are as following:

  • Your shell should give a user "tish>>" as a prompt;
  • There are two types of commands that "tish" should understand:
    • External commands: the command name is, in fact, the name of an executable file. When an external command is requested this means that the corresponding executable file should be run.
    • Internal commands: commands that are "built-in" in the "tish" shell. For example, the "bye" command does not correspond to any executable file. Instead, it causes "tish" to execute the exit system call. Below we specify which internal commands you are required to implement.
  • Execution mode for external commands:
    • Foreground: a command is given in the following form tish>> . In this mode "tish" does not return the prompt until the executable file that corresponds to the command finishes.
    • Background: a command is given in the same format as in the foreground mode, but the last parameter in the parameter list should be '&'. for example:
      tish>> emacs &
  • Example of running external commands:
    • tish>> emacs my_file.
  • List of Internal commands you are required to implement:
    • bye : terminate "tish". All background processes should be terminated. (Note that the real shell does not do this).
    • jobs : list of all background jobs in the following format: , in the order of creation.
    • kill :terminate the process corresponding to the specified pid by sending SIGTERM signal.

Recommendations and additional requirements:

  • You are required to use fork() and execvp(const char* file, const char* argv) system calls. execvp() is a version of the execve() system call in which the path and environment does not need to be specified. The file name should not! include a '/' char. If it does you should output a compatible error message. In this assignment you are required to deal with list of parameters no larger than 2. You are not required to check the type of the parameters you have received just to pass them on to the execvp() call in the right format.
  • You are NOT allowed to use the library function system() instead of fork/exec. This is because system() itself forks a new shell that forks the specified command. Using system() is absolutely prohibited in this exercise.
  • You may not assume that the user always specifies a correct input. For instance, the user may specify non-existent command name, or wrong parameters. Your program should print an appropriate error message. Note that empty or pure white space(s) command is not an error, and should be simply ignored and prompt should be repeated immediately
  • In the foreground execution mode a running process is terminated using the "Ctrl-C" key combination. Pressing this combination generates signal SIGINT that is sent to the control terminal process group. Since both "tish" and all its children are members of this group they have to take care of this signal. It should be handled differently in the main loop of "tish" (the one that provides the prompt and reads the user's input), and in a foreground child Namely:
    • Main loop of "tish" (father): ignores SIGINT, catches SIGTERM (may be sent by an outside application, e.g., tcsh);
    • Foreground child: default behavior, i.e., termination
  • When a process finishes, it enters the zombie state. A process will remain in this state as long as it father is alive. Since all external commands are children of "tish" and "tish" may be kept alive very long, the process table will eventually fill up. In this exercise you can ignore the fact that the number of zombie files in the system is limited.
  • "tish" command line is limited to 1024 characters
  • You may not assume correctness of arguments for internal commands (letters instead of numbers, negative numbers, etc. all should be checked)

System Calls and Functions List

  • fork();
  • execvp();
  • wait();
  • signal();
  • kill();
  • exit();

You may use "stdio" library functions in order to read user's input and to print the messages. You are advised to use string library functions, such as strtok() to manipulate strings.


 


Related Discussions:- Principles of operating systems

Difference among pre-emptive and non pre-emptive scheduling, Q. Define the ...

Q. Define the difference among pre-emptive and non pre-emptive scheduling. Answer: Pre-emptive scheduling permits a process to be interrupted in the midst of its execution ta

How virtual memory is implemented, How Virtual memory is implemented Vi...

How Virtual memory is implemented Virtual memory can be implemented along with Segmentation and Paging

What is the purpose of system calls, What is the purpose of system calls? ...

What is the purpose of system calls? System calls permit user-level processes to request services of the operating system.

What is dispatcher? explain, Questiion 1 What is RTOS? What are its requir...

Questiion 1 What is RTOS? What are its requirements? Questiion 2 Explain the structural elements of a real time system mode Questiion 3 What is kernel? Explain abo

Differences among user-level threads and kernel-level thread, Q. What are t...

Q. What are two differences among user-level threads and kernel-level threads? Under what situations is one type better than the other? Answer: (1) User-level threads are un

Describe the possible rmi invocation semantics, Question: (a) Explain t...

Question: (a) Explain the similarities and differences between two different threads running in the same process and two independent processes. When would you want to use two t

Page-table lookups, How exactly is a page table used to look up an address?...

How exactly is a page table used to look up an address? The CPU has a page table base register (PTBR)which points to the base (entry 0) of the level-0 page table. Each process h

Prepare a short note on the standard linux file system, Problem: a) Pre...

Problem: a) Prepare a short note on the standard Linux File System. b) Prepare a short note on the RPM Package Management Tool. c) Briefly explain the two types of login

Unix, what is difference between file descriptor and file pointer?

what is difference between file descriptor and file pointer?

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd