从我的Android服务写入/ sys

Question

大家好我正在写一个处理我的设备的LED的服务。 我喜欢写/ sys文件系统，但似乎没有工作.... 看起来是因某种原因失败，可能是权限？ 接收器工作，但无法写入/ sys ...

我的接收者：

package com.gabrielgagz.ledpearlyn;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.util.Log;
import java.io.*;

public class LedPearlynReceiver extends BroadcastReceiver {

public static boolean wasScreenOn = true;

@Override
public void onReceive(final Context context, final Intent intent) {
    if (Intent.ACTION_BOOT_COMPLETED.equals(intent.getAction())) {
        Intent serviceIntent = new Intent(context, LedPearlynService.class);
        context.startService(serviceIntent);
        Log.i("LedPearlyn","Started");
    } else if (intent.getAction().equals(Intent.ACTION_SCREEN_OFF) || intent.getAction().equals(Intent.ACTION_DREAMING_STARTED))  {
        try {
        String[] cmd = { "sh", "-c", "echo 0 > /sys/class/leds/pearlyn/brightness"};         
        Runtime.getRuntime().exec(cmd);
        } catch(IOException ie) {
        ie.printStackTrace();
        }
        wasScreenOn = false;
        Log.i("LedPearlyn","Off");
    } else if (intent.getAction().equals(Intent.ACTION_SCREEN_ON) ||  intent.getAction().equals(Intent.ACTION_DREAMING_STOPPED)) {
        try {
        String[] cmd = { "sh", "-c", "echo 255 > /sys/class/leds/pearlyn/brightness"};       
        Runtime.getRuntime().exec(cmd);
        } catch(IOException ie) {
        ie.printStackTrace();
        } 
        wasScreenOn = true;
        Log.i("LedPearlyn","On");
    }        
}
}