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

Example of semaphore, For example, by initializing a semaphore to 0, thread...

For example, by initializing a semaphore to 0, threads can wait for an event to occur, and impose an ordering constraint, similar to a monitor using condition variables, but with m

Advantage of minimizing the file space, Q. a number of systems automaticall...

Q. a number of systems automatically delete all user files when a user logs off or a job terminates unless the user explicitly requests that they be kept other systems keep all fil

Custom memory allocation, Some people write custom memory allocators to mee...

Some people write custom memory allocators to meet their speci?c needs. Although this is not needed for most of the applications, it is also not uncommon. The goal, of course, is t

What is the purpose of system programs, What is the purpose of system progr...

What is the purpose of system programs? System programs can be thought of as bundles of useful system calls. They give basic functionality to users and so users do not require

Scheduler that select process from secondary storage device, A scheduler th...

A scheduler that selects processes from secondary storage device is known as                    Medium term scheduler is a scheduler that selects processes from secondary stor

Implementation of modern memory management system , Central to implementati...

Central to implementation of a modern memory management system is the page replacement algorithm. Modern virtual memory systems break memory up into pages and map (via a page table

Define unix device driver, Define UNIX device driver The UNIX device dr...

Define UNIX device driver The UNIX device driver is structured into two halves called top half and bottom half

Is disk scheduling useful in a single-user environment, Is disk scheduling,...

Is disk scheduling, other than FCFS scheduling, useful in a single-user environment? Explain your answer. In a single-user environment, the I/O queue usually is blank. Requests

Hj, scheduling

scheduling

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