How to determine whether a given package is shipped by default in Ubuntu installation or it's installed later by the user?!
The answer in this U&L says:
To figure out if a package (Tor here) is installed by user, run this in terminal:
apt-cache show tor | grep Priority
if the priority was optional, The package was installed by user, If was standard (important on Debian ) it's a default installed package.
While a simple test for example ubuntu-desktop
$ apt-cache show ubuntu-desktop | grep Priority
gives:
Priority: optional
Then I could say this is not a proper way.
So how to determine whether the package is shipped by default or not?