What is an Orphan Processes?

An orphan process is a process in an operating system whose parent process has terminated or exited while the child process is still running. In simple terms, the parent process is no longer available to manage the child process, leaving it "orphaned." To ensure the orphan process continues to function properly, the operating system reassigns it to a system process like the init process (in Linux/Unix systems).

Orphan processes are a common occurrence and do not typically cause major issues, as they are managed automatically by the operating system.

How Does an Orphan Process Occur

An orphan process is created when:

1. The parent process terminates or crashes unexpectedly and leaves its child processes still running.
2. A parent process completes execution before its child processes finish their tasks.
3. An application design flaw causes the parent to exit before handling its child processes properly.

This program demonstrates an orphan process by creating a child process using fork(). The parent process exits immediately, leaving the child process orphaned, which is then adopted by the init process (shown by the updated parent process ID).

#include <iostream>
#include <unistd.h>
#include <sys/types.h>

int main() {
    pid_t pid;

    // Fork a child process
    pid = fork();

    if (pid > 0) {
        // Parent process
        std::cout << "Parent process (PID: " << getpid() << ") is terminating." << std::endl;
        exit(0); // Parent terminates
    } else if (pid == 0) {
        // Child process
        sleep(5); // Simulate work being done by the child
        std::cout << "Child process (PID: " << getpid() << ", PPID: " << getppid() << ") is now an orphan and adopted by init." << std::endl;
    } else {
        // Fork failed
        perror("Fork failed");
        exit(1);
    }

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main() {
    pid_t pid;

    // Fork a child process
    pid = fork();

    if (pid > 0) {
        // Parent process
        printf("Parent process (PID: %d) is terminating.\n", getpid());
        exit(0); // Parent terminates
    } else if (pid == 0) {
        // Child process
        sleep(5); // Simulate work being done by the child
        printf("Child process (PID: %d, PPID: %d) is now an orphan and adopted by init.\n", getpid(), getppid());
    } else {
        // Fork failed
        perror("Fork failed");
        exit(1);
    }

    return 0;
}

public class ProcessExample {
    public static void main(String[] args) {
        try {
            // Fork a child process
            ProcessBuilder processBuilder = new ProcessBuilder();
            Process process = processBuilder.start();

            if (process.isAlive()) {
                // Parent process
                System.out.println("Parent process (PID: " + ProcessHandle.current().getPid() + ") is terminating.");
                System.exit(0); // Parent terminates
            } else {
                // Child process
                Thread.sleep(5000); // Simulate work being done by the child
                System.out.println("Child process (PID: " + ProcessHandle.current().getPid() + ", PPID: " + ProcessHandle.current().parent().get().getPid() + ") is now an orphan and adopted by init.");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import os
import time
import sys

if __name__ == '__main__':
    # Fork a child process
    pid = os.fork()

    if pid > 0:
        # Parent process
        print(f'Parent process (PID: {os.getpid()}) is terminating.')
        sys.exit(0)  # Parent terminates
    elif pid == 0:
        # Child process
        time.sleep(5)  # Simulate work being done by the child
        print(f'Child process (PID: {os.getpid()}, PPID: {os.getppid()}) is now an orphan and adopted by init.')
    else:
        # Fork failed
        print('Fork failed', file=sys.stderr)
        sys.exit(1)

Note that the above code may not work with online compiler as fork() is disabled.

Orphan Process vs Zombie Process: Key Differences

Read more about Zombie process and their prevention.

Examples of Orphan Processes in Real Life

1. Web Servers: A web server creates child processes to handle client requests. If the server crashes, these child processes become orphaned but continue running until they finish their tasks.
2. Background Jobs: In job scheduling systems, if the scheduler (parent) crashes, its child jobs may become orphan processes.
3. Batch Processing Systems: During large-scale data processing, if a parent program managing tasks crashes, its ongoing tasks can become orphans.

Why Do Orphan Processes Matter in System Performance

• Minimal Performance Impact: Orphan processes are typically handled well by the operating system as they are reassigned to the init process for management.
• Resource Holding: If orphan processes are poorly coded, they might consume unnecessary CPU or memory resources and potentially leading to system slowdowns.
• Scalability Issues: If systems has a high volume of orphan processes, resource management can become challenging.

How Does the Operating System Handle Orphan Processes

• Reassignment to Init Process: In Linux/Unix, the init process automatically adopts orphan processes, ensuring they are monitored and cleaned up after termination.
• Proper Cleanup: The init process ensures that the orphan process’s resources (e.g., memory and file descriptors) are released when it finishes execution.

Impact of Orphan Processes

• CPU Usage: Orphan processes generally do not consume excessive CPU unless they are misbehaving or poorly coded.
• Memory Usage: Orphan processes may hold memory resources, but the OS ensures these are freed when the process ends.
• Impact on Multi-User Environments : In multi-user systems, orphan processes created by one user can indirectly affect other users by consuming shared resources, such as memory or processing power.

Orphan Process in Linux: How It Works

1. Parent-Child Process Relationship:

• A parent process creates one or more child processes to perform tasks.
• The child processes inherit the parent’s resources, such as open files, environment variables, and memory.

2. Parent Process Terminates:

• If a parent process exits unexpectedly or completes execution before its child processes finish, the child processes are left without a parent.
• At this point, the child processes become orphan processes.

3. Reassignment to Init Process:

• The Linux kernel identifies orphan processes and automatically reassigns them to the init process (process with PID 1).
• The init process is the root of all processes in Linux and is always running to ensure system stability. It acts as a caretaker for orphan processes.

4. Management by Init Process:

• Once an orphan process is reassigned to the init process, the init process becomes responsible for monitoring it.
• The init process ensures the orphan process completes its execution and properly releases its resources, such as memory and file descriptors, after termination.

5. Completion of Orphan Process:

• When an orphan process finishes its task, the init process cleans up its resources and removes its entry from the process table, preventing resource leaks.

Steps to Prevent Orphan Processes in Operating Systems

1. Parent Process Management: Design parent processes to wait for their child processes to complete using functions like wait() or waitpid().
2. Error Handling: Implement robust error-handling mechanisms to prevent parent processes from crashing unexpectedly.
3. Use Supervisors: Employ process supervisors that can restart parent processes if they fail.
4. Graceful Shutdown: Ensure parent processes terminate child processes properly during shutdown.