On Ubuntu when you install a package, there can be dependencies, recommendations and suggestions. For example: virtualbox-ose has adduser as dependency, libgl1 as recommendation and libpulse0 as suggestion.
What is the difference between recommendations and suggestions?
Recommendations are standard installed with apt. This can be prevented using the switch --no-install-recommends
Second question: How can you force to install suggestions with apt?
See Debian's FAQ about this. Ubuntu is based on Debian, so it should be the same:
Though it is a very old question, I want to write an answer here because once I searched the same question and reached here via google.
From man deb-control or https://linux.die.net/man/5/deb-control, it explains their meanings:
Recommends: <package list>
Lists packages that would be found together with this one in all but unusual
installations. The package maintenance software will warn the user if they
install a package without those listed in its Recommends field.
Suggests: <package list>
Lists packages that are related to this one and can perhaps enhance its
usefulness, but without which installing this package is perfectly reasonable.
It provides a option --install-suggests by apt-get now to install suggested packages. And it could be passed to apt.
You can avoid recommended packages from being included in an install in Synaptic via Settings, Preferences, General tab: Untick "Consider recommended packages as dependencies".
With apt-get, you can include the switch "--no-install-recommends".
Dependencies must be present to run the package. I can't tell you what specifically qualifies a package as a recommended one other than what the adjective suggests.
A CLI method of displaying dependencies and suggests is: apt-cache show Example: apt-cache show gimp
