Ubuntu failed to upgrade from Ubuntu 20.04 LTS to 20.10

[Henrique Mendonça]

When I tried to upgrade from Ubuntu 20.04 LTS to 20.10 using Ubuntu update-manager an error happens:

"Invalid package information

After updating your package information, the essential package 'ubuntu-minimal' could not be located. This may be because you have no official mirrors listed in your software sources, or because of excessive load on the mirror you are using. See /etc/apt/sources.list for the current list of configured software sources.
In the case of an overloaded mirror, you may want to try the upgrade again later."

More information:

$ lsb_release -rd
Description: Ubuntu 20.04.1 LTS
Release: 20.04

$ apt-cache policy update-manager
update-manager:
  Installed: 1:20.04.10.1
  Candidate: 1:20.04.10.1
  Version table:
 *** 1:20.04.10.1 500
        500 mirror://mirrors.ubuntu.com/mirrors.txt focal-updates/main amd64 Packages
        500 mirror://mirrors.ubuntu.com/mirrors.txt focal-updates/main i386 Packages
        100 /var/lib/dpkg/status
     1:20.04.9 500
        500 mirror://mirrors.ubuntu.com/mirrors.txt focal/main amd64 Packages
        500 mirror://mirrors.ubuntu.com/mirrors.txt focal/main i386 Packages

$ apt-cache policy apt
apt:
  Installed: 2.0.2ubuntu0.1
  Candidate: 2.0.2ubuntu0.1
  Version table:
 *** 2.0.2ubuntu0.1 500
        500 mirror://mirrors.ubuntu.com/mirrors.txt focal-updates/main amd64 Packages
        500 mirror://mirrors.ubuntu.com/mirrors.txt focal-security/main amd64 Packages
        100 /var/lib/dpkg/status
     2.0.2 500
        500 mirror://mirrors.ubuntu.com/mirrors.txt focal/main amd64 Packages

$ apt-cache policy dpkg
dpkg:
  Installed: 1.19.7ubuntu3
  Candidate: 1.19.7ubuntu3
  Version table:
 *** 1.19.7ubuntu3 500
        500 mirror://mirrors.ubuntu.com/mirrors.txt focal/main amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.28
ProcVersionSignature: Ubuntu 5.4.0-52.57-generic 5.4.65
Uname: Linux 5.4.0-52-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.11
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
Date: Sat Nov 7 09:08:59 2020
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to focal on 2020-11-07 (0 days ago)
VarLogDistupgradeAptlog:
 Log time: 2020-11-07 09:08:18.698906
 Log time: 2020-11-07 09:08:25.854096
 Log time: 2020-11-07 09:08:56.423365
 Log time: 2020-11-07 09:09:00.628915
VarLogDistupgradeTermlog:

mtime.conffile..etc.update-manager.release-upgrades: 2020-11-07T09:03:09.002716

[Brian Murray (brian-murray)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported and is a duplicate of bug 1813354, so it is being marked as such. Please look at the other bug report to see if there is any missing information that you can provide, or to see if there is a workaround for the bug. Additionally, any further discussion regarding the bug should occur in the other report. Please continue to report any other bugs you may find.