WordPress Update Failed due to Permissions

Seeing a recent update that was released for WordPress (4.2.2), I decided it was a good idea to get caught up with the version as it patched the XSS vulnerability that was discovered a few weeks prior.

At a first glance, the assumption was that it would be as easy as pressing the Update button then I was greeted with this message: The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions. More specifically the class-wp-filesystem-direct.php and update-core.php files under wp-admin/includes/.

This can be easily resolved by resetting permissions to values that are preferred by WP (more on that here).

1. Start by setting permissions of all FILES to 664: sudo find /var/www/wordpress/ -type f -exec chmod 664 {} \;
2. Then set the permissions of DIRECTORIES to 775: sudo find /var/www/wordpress/ -type d -exec chmod 775 {} \;
3. (OPTIONAL) Revert your site folder group to www-data or whatever you used for the initial setup by: sudo chgrp -R www-data /var/www/wordpress/