TYPO3 Core

If you have placed required calls in your older TYPO3 websites i.e. because of security reasons to place your password and db credentials outside of the web-accessible root or if you were working with system files which contain settings valid for all servers on your machine than the install tool won't read this data at all.

1. copy an existing localConfiguration.php file which is working to your 4.7 typo3 folder
2. change the Database credentials in this file to the one you want to convert
3. change the typo3_conf symlink from 4.7 to 6.1
4. change the password of the install tool
5. login again and you will get a Fatal Error!

This process has simply deleted all Installtool and DB credentials you had already entered into localConfiguration.php file which makes your site inaccessible incl. frontend!

Reason:
In the former localconf.php were required calls to outsourced credential and settings files i.e. the ones of image magic

All those files don't get read and processed to be converted properly to the new localConfiguration Format

Solution:
Place a Message WARNING in the Installtool About Page which warns people about this problem.
or
Make the Install Tool following properly the required calls.