In my case multiple instances of Magento are running in different directories so absolute paths were required instead of relative paths in
'cache_dir' => 'var/tmp/'
'cache_dir' => '/var/www/domain.com/var/tmp/'
This is a sample server environment, yours will be different so don't copy that line.
var/tmp already existed and permissions didn't matter. The issue in my case is a configuration apparently from the installation. When running a
diff from command line on the
/downloader/ directory there are inconsistencies in the
*.cfg files in the instances where the Magento Connect (/downloader/) would not display.