Upgrade goes to install screen

I'm trying to upgrade from 3.2 to 3.5... running on Ubuntu 16.04... moving from one machine to another

This is what I did

1. made all the backups (of course)
2. copied moodledata and moodle directories, restored database
3. tested everything in 3.2, and it works fine. 

Then for the upgrade:

1. moved the /var/www/html out of the way
   
2. uncompressed 3.5 into /var/www/html
3. copied the config.php from the working install

At that point, I get the installation screen. What have I done wrong?

Thanks in advance!