Using the file class.ext_update.php is discouraged. Use the new API as explained in this chapter.

While the update wizards already provide a skeleton and integration into TYPO3 CMS, there is a file from old times. This file is placed in the extension root and called class.ext_update.php.

If this file is found it will install a new menu item, "UPDATE", in the Extension Manager when looking at details for the extension. When this menu item is selected the class inside of this file (named ext_update) will be instantiated and the method main() will be called and expected to return HTML content.

Also the method access() has to be added. This method should return a boolean value whether or not the menu item should be shown. This feature is meant to disable the update tool if it has already been run and doesn't need to run again.