Is it possible to install dropbox under an ubuntu 14.04 server that is behind a proxy with credentials ?
You have to provide proxy authentication to install Dropbox. Here is a command using which you can do this:
sudo http_proxy="http://username:password@your_proxy:proxy_port" dropbox start -i or
sudo https_proxy="http://username:password@your_proxy:proxy_port" dropbox start -i
You have to run the deamon as root, and thus, you have to configure the proxy as root. Setting the http_proxy root env variable on invocation should be enough.