Does Pinging a machine wakes it up?

Question

I have a code to check whether a machine is alive or not.

InetAddress.getByName(IPADDRESS).isReachable(TIMEOUT);

Will this request wakes up the machine?, Or just gives a status that it is not shutdown or not accessible.

Answer 1

No, simple ping command wouldn't wake up your machine regardless of its configuration. You would want to use a "wake-on-lan" command, which has to contain the machine's MAC address above all, IP address itself is insufficient. Also, the machine has to support the feature (more precisely, the network adapter is uses has to), and it has to be enabled, so make sure that is done.

I'm including the example I've referred to in the past on how to implement this in java:

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

public class WakeOnLan {

public static final int PORT = 9;    

public static void main(String[] args) {

    if (args.length != 2) {
        System.out.println("Usage: java WakeOnLan <broadcast-ip> <mac-address>");
        System.out.println("Example: java WakeOnLan 192.168.0.255 00:0D:61:08:22:4A");
        System.out.println("Example: java WakeOnLan 192.168.0.255 00-0D-61-08-22-4A");
        System.exit(1);
    }

    String ipStr = args[0];
    String macStr = args[1];

    try {
        byte[] macBytes = getMacBytes(macStr);
        byte[] bytes = new byte[6 + 16 * macBytes.length];
        for (int i = 0; i < 6; i++) {
            bytes[i] = (byte) 0xff;
        }
        for (int i = 6; i < bytes.length; i += macBytes.length) {
            System.arraycopy(macBytes, 0, bytes, i, macBytes.length);
        }

        InetAddress address = InetAddress.getByName(ipStr);
        DatagramPacket packet = new DatagramPacket(bytes, bytes.length, address, PORT);
        DatagramSocket socket = new DatagramSocket();
        socket.send(packet);
        socket.close();

        System.out.println("Wake-on-LAN packet sent.");
    }
    catch (Exception e) {
        System.out.println("Failed to send Wake-on-LAN packet: + e");
        System.exit(1);
    }

}

private static byte[] getMacBytes(String macStr) throws IllegalArgumentException {
    byte[] bytes = new byte[6];
    String[] hex = macStr.split("(\\:|\\-)");
    if (hex.length != 6) {
        throw new IllegalArgumentException("Invalid MAC address.");
    }
    try {
        for (int i = 0; i < 6; i++) {
            bytes[i] = (byte) Integer.parseInt(hex[i], 16);
        }
    }
    catch (NumberFormatException e) {
        throw new IllegalArgumentException("Invalid hex digit in MAC address.");
    }
    return bytes;
}


}