Restart apache

sudo /etc/init.d/apache2 restart

Change folder permissions in ubuntu

sudo chmod -R 777 folder_name

File permissions in ubuntu

gksu nautilus

Delete a symbolic link in ubuntu

sudo unlink filename

Drupal Custom Theme Not Detected

Generally this problem arises when the .info file is not correctly configured. Check the contents of the file and the extension of the file. It should be theme_name.info and not theme_name.info.txt or any other file extension.