issue never comes up in terminal. sudo apt-get install works fine. must be a software center bug. it happened just after updating this morning...
temporarily solved by changing permissions to software center. now i don't need root to use it.
Samsung Galaxy S3 (Stock, rooted TouchWiz)
Samsung Galaxy Tab 3 7.0 (non-rooted, stock)
Samsung Galaxy Tab 2 10.1 (obsolete, slow, rooted)
Samsung Galaxy Note 10.1 2014 Edition