How To make sure any file or folder created in /var/www/html gets automatically owned by www-data

To make sure any file or folder you create in /var/www/html gets automatically owned by www-data you can use inotify, it's like cron but monitors folders/files for changes in attributes, file creations, modifications and much more.

First install it with:

$ sudo apt-get install incron
Allow root to use incron by opening /etc/incron.allow with:

$ sudo vim /etc/incron.allow
and add root to the file, then save and exit.

Edit your incrontab with:

$ sudo incrontab -u root -e
and add the following line to it:

/var/www/html IN_CREATE /bin/chown -R www-data:www-data /var/www/html/
save and exit.

Now as soon as a file is created in the /var/www/html directory it will automatically set ownership to www-data:www-data.

Explanation of the line in incrontab:

/var/www/html is the directory that will be monitored.

IN_CREATE will watch for created files. It's the file change mask.

/bin/chown -R www-data:www-data /var/www/html/ is the command/action to execute.