Magento 2

https://magento.stackexchange.com/questions/216720/sqlstate23000-integrity-constraint-violation-1062-duplicate-entry-magento?rq=1

cd <your Magento install dir> 

find . -type f -exec chmod 644 {} \;                        // 644 permission for files

find . -type d -exec chmod 755 {} \;                        // 755 permission for directory 

find ./var -type d -exec chmod 777 {} \;                // 777 permission for var folder    

find ./pub/media -type d -exec chmod 777 {} \;

find ./pub/static -type d -exec chmod 777 {} \;

chmod 777 ./app/etc

chmod 644 ./app/etc/*.xml

If default.xml on your custom theme is not loading, it is possible that your theme is set to virtual (1) in the database.

Go to theme table and change type value to 0. After clear cache it's effects should be visible

Sometimes, when trying to install a Magento 2 module via Composer you get the error: Invalid credentials for 'https://repo.magento.com/packages.json', aborting.

Magento 2 frontend development can be really frustrating some times.

In order to ensure you can view the modifications of layout files folow the next steps: