I have an older computer and a slowish connection. How can I get apt to
upgrade one package at a time? Generally, if you upgrade it will
download all the packages and then, once they're downloaded, upgrade.
I suppose the other approach is to set apt to just download packages and
then at a later date, once they're all downloaded, upgrade all the
packages. I've never been really clear on how to know when the packages
are downloaded or what the next step is.