use o argumento --dry-run , -s , --simulate , --just-print , --recon , --no-act e ele não fará nada de fato, apenas informará o que ele faria:
Da página de manual do apt-get
-s, --simulate, --just-print, --dry-run, --recon, --no-act
No action; perform a simulation of events that would occur but do
not actually change the system. Configuration Item:
APT::Get::Simulate.
Simulate prints out a series of lines each one representing a dpkg
operation, Configure (Conf), Remove (Remv), Unpack (Inst). Square
brackets indicate broken packages with and empty set of square
brackets meaning breaks that are of no consequence (rare).
então dê uma olhada no comando:
apt-get upgrade --dry-run
ou
apt-get upgrade -s