Linux Shell with Process Scheduling

Overview

This project implements a custom Linux shell with basic command execution and process scheduling capabilities. It uses shared memory and semaphores to manage and schedule processes, and it maintains a history of executed commands.

Features

• Basic Shell Functionality: Execute standard shell commands.
• Process Scheduling: Submit and schedule processes with different priorities.
• Shared Memory: Utilize shared memory to communicate between parent and child processes.
• Semaphores: Ensure proper synchronization using semaphores.
• History Tracking: Keep a history of executed commands.
• Signal Handling: Gracefully handle the termination signal (Ctrl+C) to print process information before exiting.

Structures

schedInfo

Stores information about a scheduled process.

typedef struct schedInfo {
    int pid;
    char name[1000];
    int execTime;
    int waitTime;
    int priority;
} schedInfo;

execInfo

Stores information about an executed child process.

typedef struct execInfo {
    int pid;
    time_t timeExecuted;
    float duration;
    int exitStatus;
} execInfo;

shmbuf

Shared memory buffer structure.

typedef struct shmbuf {
    int isRunning;
    sem_t sem_lock;
    sem_t sem_check;
    int ncpu;
    int tslice;
    int pid_cnt;
    schedInfo pids[BUF_SIZE];
    int completed_cnt;
    schedInfo completed[BUF_SIZE];
    int pids_completed_cnt;
    int pids_completed[BUF_SIZE];
} shmbuf;

Functions

void shm_init(char *shmpath, int ncpu, int tslice)

Initializes shared memory and semaphores.

void printProcessInfo()

Prints information about all executed processes.

void history()

Prints the history of executed commands.

void create_process_and_run(char **args, int argscount)

Creates and runs child processes based on the provided arguments.

void launch(char *userInput)

Parses user input and executes the appropriate command.

void exit_program()

Handles the termination signal (Ctrl+C) and prints process information before exiting.

Usage

Compilation

Compile the code using gcc:

gcc -o custom_shell custom_shell.c -pthread -lrt

Execution

Run the compiled program:

./custom_shell

Commands

• Basic Commands: Any standard shell command can be executed.
• Submit Commands: Use the submit keyword to schedule a process. For example, submit ls -l.
• History: The history command prints the history of executed commands.

Sample Interaction

Enter number of CPUs: 2
Enter tslice in milliseconds: 100

Waiting for scheduler
Scheduler hooked

> ls
<output of ls command>

> submit ls -l
<scheduled output of ls -l command>

> history
ls
submit ls -l

Notes

• Ensure you have appropriate permissions to create shared memory objects.
• The submit keyword is used to schedule commands with a specified priority.
• The program gracefully handles Ctrl+C, printing process information before exiting.

Dependencies

• pthread library: Used for semaphores.
• librt: Used for shared memory.

gcc -o custom_shell custom_shell.c -pthread -lrt