[Bug 1771852] Re: In update-manager I see error "no internet connection", but it isn't true. And update of Ubuntu is no possible for me

[Pavol]

Jean, thank you very much for help!
Now I have successfully installed Ubuntu 18.04! 
It is perfect release: light and very quick OS.

But I see other bugs:
- in login manager, when I choose other graphical interface / environment, after login into, I see empty screen only with background picture. Developer team of Ubuntu probably never tested Ubuntu 18.04 for switch on other graphical interfaces

- Ubuntu Software is no possible for use. It work on experimental Snap
packages. Installation of applications is no possible

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https://bugs.launchpad.net/bugs/1771852

Title:
  In update-manager I see error "no internet connection", but it isn't
  true. And update of Ubuntu is no possible for me

Status in ubuntu-release-upgrader package in Ubuntu:
  Invalid

Bug description:
  software-properties-gtk probably doesn't work correct too.
  I am desperate. Update of Ubuntu doesn't work for me :(.
  I use Ubuntu with Cinnamon graphical interface.
  I reinstalled software-propertie and software-propertie via Synaptic, but it doesn't help me.
  I have Slovak language in Ubuntu.
  I send you more screen-shots. 
  (you support only one file in attachment, I send you screen-shots in zip file)

  ProblemType: Bug
  DistroRelease: Ubuntu 17.10
  Package: ubuntu-release-upgrader-core 1:17.10.11
  ProcVersionSignature: Ubuntu 4.13.0-41.46-generic 4.13.16
  Uname: Linux 4.13.0-41-generic x86_64
  ApportVersion: 2.20.7-0ubuntu3.8
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: X-Cinnamon
  Date: Thu May 17 17:29:08 2018
  InstallationDate: Installed on 2016-12-03 (529 days ago)
  InstallationMedia: Ubuntu-GNOME 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160720)
  PackageArchitecture: all
  ProcEnviron:
   LANGUAGE=sk_SK
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=sk_SK.UTF-8
   SHELL=/bin/bash
  SourcePackage: ubuntu-release-upgrader
  Symptom: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to artful on 2018-05-17 (0 days ago)
  VarLogDistupgradeAptlog:
   Log time: 2018-05-17 16:20:23.507926
   Log time: 2018-05-17 16:20:35.638775
   Log time: 2018-05-17 16:24:37.386152
  VarLogDistupgradeTermlog:

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