以编程方式重启android设备

ImageButton restartmob = (ImageButton) this.findViewById(R.id.restartmob);
    restartmob.setonClickListener(new ImageButton.OnClickListener() {
        @Override
        public void onClick(View v) {
            Process proc = null;            
            try {
               //proc = Runtime.getRuntime().exec(new String[] { "su","-c","reboot" });
                 proc = Runtime.getRuntime().exec(new String[]{"/system/bin/su","reboot Now"});
                proc.waitFor();
            } catch (Exception ex) {
                Log.i(TAG,"Could not reboot",ex);
            }
        }
    });

我还在清单文件中添加了以下权限.

<permission android:name="android.permission.REBOOT"/>

当我单击图像按钮重新启动时,我得到以下异常.

java.io.IOException: Error running exec(). Command: [/system/bin/su,-c,reboot Now] 
Working Directory: null Environment: null   
at java.lang.ProcessManager.exec(ProcessManager.java:211)   
at java.lang.Runtime.exec(Runtime.java:173)
at java.lang.Runtime.exec(Runtime.java:128)
at com.android.onlinepayment.activity.SystemSubMenuActivity$1.onClick(SystemSubMenuActivity.java:49)
at android.view.View.performClick(View.java:5184)   
at android.view.View$PerformClick.run(View.java:20910)  
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5942)    
at java.lang.reflect.Method.invoke(Native Method)   
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1388  
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1183)
Caused by: java.io.IOException: No such file or directory   
at java.lang.ProcessManager.exec(Native Method)
at java.lang.ProcessManager.exec(ProcessManager.java:209)
... 13 more

我的代码出了什么问题？请帮帮我.
对于信息,我正在测试android Lollipop(如果它很重要).
提前致谢.