I cannot upgrade to the new Ubuntu long-term support version.

[Vassil Zhivkov]

The system claims it cannot locate a mirror server to upgrade to a new Ubuntu edition. It can update the existing version 14 though.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.9 [origin: unknown]
ProcVersionSignature: Ubuntu 3.13.0-135.184-generic 3.13.11-ckt39
Uname: Linux 3.13.0-135-generic i686
ApportVersion: 2.14.1-0ubuntu3.25
Architecture: i386
CrashDB: ubuntu
Date: Sun Dec 3 16:42:15 2017
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=bg_BG:bg:en_GB:en
 PATH=(custom, no user)
 LANG=bg_BG.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2017-12-03 (0 days ago)
VarLogDistupgradeAptlog:
 Log time: 2017-12-03 16:28:28.637911
 Log time: 2017-12-03 16:29:08.020182
 Log time: 2017-12-03 16:30:31.055289
 Log time: 2017-12-03 16:42:25.787085
VarLogDistupgradeTermlog: