Impossible de chercher un mise a jour via le gestionnaire de miser a jour. /Unable to seek an update via the Manager bet update.

david@david-VirtualBox:~$ lsb_release -rd
Description: Ubuntu Xenial Xerus (development branch)
Release: 16.04

david@david-VirtualBox:~$ apt-cache policy pkgname
N: Impossible de trouver le paquet pkgname

Unable to update Ubuntu via the Update Manager.

Impossible de mettre a jour Ubuntu via le gestionnaire de mise a jour.

Cordialy David

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.1 [origin: unknown]
ProcVersionSignature: Ubuntu 4.2.0-17.21-generic 4.2.3
Uname: Linux 4.2.0-17-generic i686
ApportVersion: 2.19.2-0ubuntu1
Architecture: i386
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sat Oct 31 15:12:26 2015
InstallationDate: Installed on 2015-07-19 (103 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release i386 (20150422)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: release-upgrade
UpgradeStatus: No upgrade log present (probably fresh install)
VarLogDistupgradeTermlog: