Your software
My PHP version is : 7.2
*My MariaDB version is: 10.2
Updating/Installing Errors
*I am: Updating
*Upgrading: Command Line
These errors are showing in the installer :
No errors all looked good at this stage:
Welcome to Phase 2 of the Mautic 3 upgrade! We’ll continue where we left off.
Moving Mautic 2 files into mautic-2-backup and moving the Mautic 3 files in place, this might take a while… DO NOT ABORT THE SCRIPT!!!
Done!
Updating your config/local.php with new settings that were changed/introduced in Mautic 3…
Done! Your config file has been updated.
Getting the amount of available Mautic 3 database migrations… This might take a while!
Applying Mautic 3 database migrations, 9 migrations in total… This might take a while!
All Mautic 3 migrations applied successfully.
Restoring your user data like custom plugins/themes/media from the Mautic 2 installation. This might take a while… DO NOT ABORT THE SCRIPT!!!
Done! Your user data has been restored. Your Mautic 3 installation is ready. Just one more thing:
Cleaning up installation files that we no longer need…
Cleaned up successfully!
Building cache for Mautic 3…
Done! Cache has been built.
We’re done! Enjoy using Mautic 3 
Don’t forget to update your cron jobs!
Do you want to remove the backup files? We recommend first checking in a browser whether Mautic 3 works as expected. Type “yes” to remove:
no
Ok, we won’t do anything for now. Please note that upgrade_v3.php will remain (publicly) available until you choose to remove the backup files using this script! Run this script again to be prompted to delete backup files.
These errors are showing in the Mautic log :
2020/07/24 13:29:41 [error] 30135#30135: *48256 FastCGI sent in stderr: “PHP message: RuntimeException: Unable to write in the “cache” directory (/var/www/mautic/app/…/var/cache/prod). - in file /var/www/mautic/vendor/symfony/http-kernel/Kernel.php - at line 768” while reading response header from upstream, client: ip.ip.ip.ip, server: mydomain.com, request: “GET / HTTP/2.0”, upstream: “fastcgi://unix:/run/php/php7.2-fpm.sock:”, host: “mydomain.com”
These errors are showing in the upgrade_log.txt file (located in the root of your Mautic instance when an upgrade has been attempted - ensure you remove or redact any sensitive data such as domain names in the file path) :
None
Your problem
My problem is :
The above was my problem. When started looking at the files in the directory I noticed that everything was owned by root.
ran chown -R www-data:www-data * and fixed everything
Steps I have tried to fix the problem :
