www-data group issue with wordpress file permissions

You write:

Wordpress wasn't able to write so I did the following:

added my user to data group
sudo usermod -a -G www-data myusername

then
sudo chown -R www-data:www-data /var/www/example.com/public_html

This was like using a sledge hammer to repair fine jewelry! As you found out…

What you should have done is:

sudo chown www-data:sftp /var/www/example.com…
sudo chmod g+w /var/www/example.com…

on the VERY FEW directories that require write access by the web server and sftp (usually those that can receive uploads). sftp above represents the group for sftp.

You should consult the Wordpress docs and find out exactly which directories under /var/www/example.com/… need to writable by www-data and whatever the sftp user/group is and do the above ONLY on those.

Lastly, you should be using correct terminology. "Wordpress" is not a 'thing' on a Linux system…it's a PHP application that runs under the auspices of a web server. The 'thing' is the web server (Apache in your case). Apache has user/group www-data.

-- sw