After migrating my Apache server from Ubuntu 14.04 to CentOS 7, I started experiencing these permission errors.
On the Magento Connect Manager login page, I'm hit with an error message and unable to login:
Unable to write to the configuration file.
The error remained even after I set the permission for every file and folder to 0777.
I then deleted the .cfg files in the "downloader" folder. Now the error message has become:
Settings has not been loaded. Used default settings Config file does not exists please save Settings Unable to write to the configuration file.
After login/logout, restarting the Apache server and even the entire host, the error remained. The error logs did not record anything at all.
Solved!
SELinux was preventing Apache from writing to the directory. I used the following command to enable it:
chcon -t httpd_sys_rw_content_t /var/www/html -R