[...]
I have tried to come up with possible reasons why some people have such
bad experiences when they try aptitude. Here is my "traps and pitfalls
of aptitude" list:
1) Aptitude remembers intended actions, even if you change the package
states and/or configuration settings which prompted this behavior.
When in doubt, run "aptitude keep-all".
2) Aptitude tries to react immediately to changes in package states,
including the "automatically installed" flag. If you want to run
several successive (un)markauto commands to change/fix your system
then you have to use "--schedule-only" to keep aptitude from doing
something unintended halfway through the operation and "keep-all"
afterwards. Another helpful stop-gap measure in such cases is
-o aptitude::Keep-Unused-Pattern='~T'
3) The location of aptitude's configuration file depends on whether it
is run as root or with "sudo" (unless you change your sudo set_home
configuration). This can lead to inconsistent behavior. "sudo -H"
takes care of this.
4) If aptitude runs into problems when trying to upgrade packages (e.g.
because the updated versions of some dependencies are still missing)
it will normally propose the least harmful action first (e.g. keeping
a few packages at their presently installed version). However, if you
run another upgrade command after the harmless actions have been
carried out, then aptitude will assume that you want it to be more
aggressive. "keep-all" helps again, as well as CTRL + U or "Cancel
Pending Actions" in interactive mode.