Add the User ID column to the WordPress Users Table

add_user_id.php

/*
copy the following code to you current theme functions.php file:
*/

/*
 * Adding the column
 */
function rd_user_id_column( $columns ) {
	$columns['user_id'] = 'ID';
	return $columns;
}
add_filter('manage_users_columns', 'rd_user_id_column');
 
/*
 * Column content
 */
function rd_user_id_column_content($value, $column_name, $user_id) {
	if ( 'user_id' == $column_name )
		return $user_id;
	return $value;
}
add_action('manage_users_custom_column',  'rd_user_id_column_content', 10, 3);
 
/*
 * Column style (you can skip this if you want)
 */
function rd_user_id_column_style(){
	echo '<style>.column-user_id{width: 5%}</style>';
}
add_action('admin_head-users.php',  'rd_user_id_column_style');