В менеджере обновлений выбрано "Для версий с длительным сроком поддержки".
В ответ на sudo update-manager -c выдает
Traceback (most recent call last):
File "/usr/bin/update-manager", line 26, in <module>
from gi.repository import Gtk
File "/usr/lib/python2.7/dist-packages/gi/importer.py", line 76, in load_module
dynamic_module._load()
File "/usr/lib/python2.7/dist-packages/gi/module.py", line 224, in _load
overrides_modules = __import__('gi.overrides', fromlist=[self._namespace])
File "/usr/lib/python2.7/dist-packages/gi/overrides/Gtk.py", line 1404, in <module>
raise RuntimeError("Gtk couldn't be initialized")
RuntimeError: Gtk couldn't be initialized