I attempted to upgrade my Craft CMS 2.7 website to 3.0 following the instructions on:
https://docs.craftcms.com/v3/upgrade.html#preparing-for-the-upgrade
I think that I have followed everything correctly, but my result was a blank page. I have done some searching on this, and I am not getting any help. Any suggestions?
I went to my apache error logs and found out that Craft CMS couldn't open the vendor/autoload.php file. And, that was producing a blank page because CraftCMS couldn't even load anything because it couldn't load this file.
It ended up being a permissions issue. I thought I have given it the right permission, and I had not. In this case:
sudo chmod 774 -R vendor/
after that, I was getting the craft error messages and then I had to change the permissions on a few others that I thought I had already done.