アップデートのためアップグレードできませんが、サポートが終了しているため更新できません

アップデートのためアップグレードできませんが、サポートが終了しているため更新できません

18.04.6 LTS を次の LTS にアップグレードしたいのですが、先に実行すべき更新があると思われるため、アップグレードできません。ただし、これらの更新は機能せず、「インターネット接続を確認してください」というエラーが表示されます。これは、現在、これらの更新が拡張サポートとしてのみ利用可能になっているためだと思います。

old-releases.ubuntu.com を使用するように /etc/apt/sources.list を変更してみましたが、効果がないようです。

# deb cdrom:[Ubuntu 14.04 LTS _Trusty Tahr_ - Release amd64 (20140417)]/ trusty main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://old-releases.ubuntu.com/ubuntu bionic main restricted
deb-src http://old-releases.ubuntu.com/ubuntu bionic main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://old-releases.ubuntu.com/ubuntu bionic-updates main restricted
deb-src http://old-releases.ubuntu.com/ubuntu bionic-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://old-releases.ubuntu.com/ubuntu bionic universe
deb-src http://old-releases.ubuntu.com/ubuntu bionic universe
deb http://old-releases.ubuntu.com/ubuntu bionic-updates universe
deb-src http://old-releases.ubuntu.com/ubuntu bionic-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://old-releases.ubuntu.com/ubuntu bionic multiverse
deb-src http://old-releases.ubuntu.com/ubuntu bionic multiverse
deb http://old-releases.ubuntu.com/ubuntu bionic-updates multiverse
deb-src http://old-releases.ubuntu.com/ubuntu bionic-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://old-releases.ubuntu.com/ubuntu bionic-backports main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu bionic-backports main restricted universe multiverse

deb http://old-releases.ubuntu.com/ubuntu bionic-security main restricted
deb-src http://old-releases.ubuntu.com/ubuntu bionic-security main restricted
deb http://old-releases.ubuntu.com/ubuntu bionic-security universe
deb-src http://old-releases.ubuntu.com/ubuntu bionic-security universe
deb http://old-releases.ubuntu.com/ubuntu bionic-security multiverse
deb-src http://old-releases.ubuntu.com/ubuntu bionic-security multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://old-releases.ubuntu.com/ubuntu bionic partner
deb-src http://old-releases.ubuntu.com/ubuntu bionic partner`
$ sudo apt update
Ign:1 http://old-releases.ubuntu.com/ubuntu bionic InRelease
Ign:2 http://old-releases.ubuntu.com/ubuntu bionic-updates InRelease
Ign:3 http://old-releases.ubuntu.com/ubuntu bionic-backports InRelease
Ign:4 http://old-releases.ubuntu.com/ubuntu bionic-security InRelease
Err:5 http://old-releases.ubuntu.com/ubuntu bionic Release
  404  Not Found [IP: 185.125.190.37 80]
Err:6 http://old-releases.ubuntu.com/ubuntu bionic-updates Release
  404  Not Found [IP: 185.125.190.37 80]
Err:7 http://old-releases.ubuntu.com/ubuntu bionic-backports Release
  404  Not Found [IP: 185.125.190.37 80]
Hit:8 https://esm.ubuntu.com/infra/ubuntu bionic-infra-security InRelease
Err:9 http://old-releases.ubuntu.com/ubuntu bionic-security Release     
  404  Not Found [IP: 185.125.190.37 80]
Hit:10 https://esm.ubuntu.com/infra/ubuntu bionic-infra-updates InRelease
Reading package lists... Done                     
E: The repository 'http://old-releases.ubuntu.com/ubuntu bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://old-releases.ubuntu.com/ubuntu bionic-updates Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://old-releases.ubuntu.com/ubuntu bionic-backports Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://old-releases.ubuntu.com/ubuntu bionic-security Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

答え1

そうですね、/etc/apt/source.list を old-releases.ubuntu.com に変更したのは間違っていたようで、役に立ちませんでしたが、GUI で下の 4 つまたは 5 つのチェックを外すと、突然アップグレードのロックが解除されました。

最初からすべてのソースのチェックを外すだけでもうまくいったのではないかと思うのですが、残念ながらこれ以上テストすることはできません。

アップグレードは問題なく完了したようです。

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