When you try to upgrade a WordPress installation, you get the dreaded error:
Could not copy files. Installation failed.
This means that ftp is installed on your server but there is an ownership problem.
Just give ownership of the html folder to the user created while installing Vsftpd with this command:
# chown -R lion /usr/local/nginx/html
(Change ‘lion’ to the user’s name and check the folder address).
Now, when you go on to upgrade, it should work flawlessly.
If you still get an error, it means there are permission errors. Just chmod the wordpress core files to 777 and you should be okay.
# cd /home/nginx/domains/mysite/public
# chmod -R 777 *
R means that a recursive change will be made.