//if the user clicks the "View by Text" button, the div named "monshow_data" will show
// the text data from the "monshow" command;
//and , if the "view by Graphics" button is clicked, the "monshow_data" div will display the pictures, the pictures is generated by "rrdtool" right now, but in the future, some jQuery plugin will be used to generate the graphics for the "monshow" data