How To Simulate Linux Package Upgrade Without Installing Anything ( Dry Run )

Q. How do I simulate the upgrade first to confirm that the actions that would be taken are reasonable under Debian / Ubuntu Linux package management?

A. Dry run is really good idea under for all production servers. You can print the actions that would normally be performed, but don't actually perform them. This does not require root privileges. It is recommended that you simulate the upgrade first to confirm that the actions that would be taken are reasonable. The upgrade may be simulated by issuing the command:
# aptitude -s -y dist-upgrade
OR
$ sudo aptitude -s -y dist-upgrade
Sample output:

 aptitude -s -y dist-upgrade
Reading package lists... Done
Building dependency tree... Done
Reading extended state information
Initializing package states... Done
Reading task descriptions... Done
Building tag database... Done
The following packages are unused and will be REMOVED:
  libgssapi2
The following packages will be upgraded:
  libpcre3
1 packages upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
Need to get 0B/199kB of archives. After unpacking 119kB will be freed.
Would download/install/remove packages.