"The following packages will be kept back"
If during a $ sudo apt-get upgrade you see a message that
"The following packages will be kept back" followed by one or more package names, it means that the upgrade would require another package to be deleted, or a new package to be installed so that yours can be installed.
To actually complete the install, run:
sudo apt-get --with-new-pkgs upgrade
This will first alert you to what other packagers need to be deleted or installed to get your desired one installed.