Thought the specifics are fairly useless, Unless you want to find out exactly what changes were made to the system on a specific day and time, I felt the steps I went through to discover this information were worth documenting:

I ran strace -e trace=open -f -o usc software-center to get a list of all the files opened by the software center. Then I filtered it like this.

cat usc| grep -oP '(?<=open(").*(?=",)' |egrep -v '.(so.([0-9]|cache)|so|pyc|mo|py|png|svg)$'|egrep -v '/usr/lib/(python2.7|x86|girepo)'| egrep -v '/usr/share/(icons|themes)' |egrep -v '/etc/fonts'|egrep -v '(screenshots|reviews).ubuntu.com' |egrep -v fontconfig |sort -u

to eliminate all the files didn't contain data files.

Among these I found the interesting looking looking file: ~/.cache/software-center/apthistory.p It looked like a python pickle file when I opened it. trying to load the file I got the error that softwarecenter.db.history_impl.apthistory was not imported. I ran the following command to look for python files that ere opened and had "softwarecenter" in their path

$cat usc| grep -oP '(?<=open(").*(?=",)' |grep softwarecenter

and got a whole bunch of filenames including /usr/share/software-center/softwarecenter/db/history_impl/apthistory.so I wrote the following script to read and process file:

#!/usr/bin/python

import sys

import os

import pickle



sys.path.append('/usr/share/software-center')

import softwarecenter.db.history_impl.apthistory



with open(os.path.expanduser('~/.cache/software-center/apthistory.p')) as IFile:

    hist=pickle.load(IFile)



print type(hist[0])

print "earliest apt transaction started on:",hist[-1].start_date

print "installed:"

for PackageStr in hist[-1].install:

    print PackageStr

print "upgraded:"

for PackageStr in hist[-1].upgrade:

    print PackageStr

I found the necessary attributes by looking up the class of which hist[0] was an instance of: help(softwarecenter.db.history_impl.apthistory.AptTransaction). This lead me to the parent class help( softwarecenter.db.history.Transaction) from where I figured out how to use it.

Btw even sudo apt-get installed stuff appears here.