Function to get thumbnail img source

wp_get_attachment_url( get_post_thumbnail_id($post->ID) );

all together:

    <div class="entry-thumbnail">
       <a rel="lightbox" href="https://wordpress.stackexchange.com/questions/107218/<?php echo wp_get_attachment_url( get_post_thumbnail_id($post->ID) ); ?>"><?php echo get_the_post_thumbnail( $post->ID ); ?></a>
    </div> 

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)