Problem

Failed to connect to FTP server

To perform the requested action, WordPress needs to access your web server. Please enter your FTP credentials to proceed. If you do not remember your credentials, you should contact your web host.

(Followed by a form for FTP username, password and protocol – FTP/SFTP)

Solution

Ubuntu

chown -Rf user.group /path/to/root

Apache/Centos

sudo chown -R apache.apache /path/to/root

Apache/Centos

sudo chown -R nginx:nginx /path/to/root

path/to/file is the server root path for the public folder, on many systems this is var/www/