"invalid login" when attempting to update Joomla 3.4.8 to 3.7.5

Question

At /administrator/index.php?option=com_joomlaupdate I click Install the update to update from 3.4.8 to 3.7.5, but immediately after clicking that button I receive a browser popup window invalid login.

I am logged into Joomla okay with a super user account, and the database user has full rights to the database.

After I click OK to the invalid login message, I am taken to the update screen where nothing happens.

If I visit Extensions > Manage > Install, and try and upload Joomla_3.5.1-Stable-Full_Package the screen will refresh and nothing happens.

If I unzip Joomla_3.5.1-Stable-Full_Package into the site's directory, and refresh admin (after deleting the installation folder), I get a pile of errors at Extensions > Manage > Database > Fix.

Help appreciated.

Answer 1

Please note that you can not update directly from Joomla! lower than 3.6.5 (3.0.0 to 3.6.4 inclusive) to Joomla! 3.6.5 or later using the extensions manager. You need to use Joomla! Update or perform a manual update.

I assume you cannot use Joomla! Update if you are asking this question. Presumably your server is firewalled and cannot download the update directly. Therefore you need to follow Method C in the Joomla! documentation on core updates.

Do note that later versions of Joomla! Update include their own upload and install for Joomla! core updates (I contributed that feature). Upgrading to the next Joomla! versions will be possible from Joomla! Update even if it cannot download the update package directly. There will be a second tab at the top of its page which allows you to use an upload & install method.

Answer 2

Try to install a fresh 3.4.8 on the same machine, same place, keep all things equal.
If this doesn't work, there's a problem with your server and Joomla should tell you something about the problem (too old versions of PHP or MySQL, bad permissions etc.)
If it works do the update.
If it works :
1/ you can try to search for differences between the 2 installations. On Linux :

diff -r <<old_installation>> <<fresh_installation>>

you should find something...
NB : if you use many plugins, extensions etc. it's gonna be more complicated. You will have to install all of them before the diff -r. May be you'll find the one that causes the problem during this installations...
but :
2/ You've got an installation which is OK: the fresh one ! You just have to modify the section of configuration.php concerning MySQL (DB name, username and password). Since you just updated it, why not trying... If it doesn't work, try to fix the DB : Extensions -> Manage -> Database, Fix button. If it doesn't work, do the same on a fresh 3.4.8 and update.
If on different machines, you may need :

mysqldump -u root -p<<password>> --opt <<old_DB>> > temp.sql

to dump the DB from one machine and

 mysql -u root -p<<password>> <<new_DB>> < temp.sql

to create it on the new machine.
Don't forget the command :

chown -R www-data:www-data <<Joomla_dir>>

when you modify files here and there ;)