Question

I was given this sample code from college today and it worked fine inside the college but when I run it (using Eclipse) on my home machine I get permission denied. The machine in college is Windows (7) and my computer at home is Linux (Ubuntu).

Why am I getting the following error?

Error in I/O
Permission denied

I’m using port 338.

Copy of the code :

import java.io.*;
import java.net.*;
import java.util.*;

public class Server 
{
    public static void main(String[] args)
    {
        try
        {
            // First create the input from the keyboard
            BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("Server Program");

            // Get the port to listen on
            System.out.print("Enter port number to listen on: ");
            String port_string = input.readLine();

            // The port number needs to be an int, so convert the String to an int
            int port = Integer.parseInt(port_string);

            // Create a ServerSocket to listen on this address
            ServerSocket server = new ServerSocket(port);

            // Accept an incoming client connection on the server socket
            Socket sock = server.accept();

            // Create the output stream to the client
            DataOutputStream network = new DataOutputStream(sock.getOutputStream());

            // Send message
            network.writeUTF("Welcome " + sock.getInetAddress().getHostName() + ". We are " + new Date() + "\n");

            // Close sockets.  This will cause the client to exit
            sock.close();
            server.close();
        }
        catch (IOException ioe)
        {
            System.err.println("Error in I/O");
            System.err.println(ioe.getMessage());
            System.exit(-1);
        }
    }
}

Answer 1

Ports under 1024 are on most modern OS’s (Ubuntu included) privileged, and require you to run the program as administrator/root or with elevated privileges.

Try a higher port for testing at home and you should be ok.