私が実行すると、sudo apt-get updateこれは私が得るものです
E: The repository 'http://in.archive.ubuntu.com/ubuntu cosmic 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://in.archive.ubuntu.com/ubuntu cosmic-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://in.archive.ubuntu.com/ubuntu cosmic-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://security.ubuntu.com/ubuntu cosmic-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.
W: GPG error: https://dl.bintray.com/apache/cassandra 311x InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F1000962B7F6840C
E: The repository 'http://www.apache.org/dist/cassandra/debian 311x InRelease' is not signed.
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.
W: Target Packages (main/binary-amd64/Packages) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target Packages (main/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target Translations (main/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target DEP-11 (main/dep11/Components-amd64.yml) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target DEP-11 (main/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target DEP-11-icons-small (main/dep11/icons-48x48.tar) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target DEP-11-icons (main/dep11/icons-64x64.tar) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target CNF (main/cnf/Commands-amd64) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list.d/cassandra.list:1 and /etc/apt/sources.list.d/cassandra.sources.list:1
今は何もインストールできません。
ベストアンサー1
Ubuntu 18.10（Cosmic Cuttlefish）は2019年7月に寿命が終了し、Ubuntuアーカイブから削除されました。現時点では、いくつかの深刻なセキュリティ問題があるため、できるだけ早くサポートされているバージョンにアップグレードする必要があります。
残念ながら、Ubuntuは非LTSバージョン（18.10など）から次のLTS 20.04へのアップグレードをサポートしていないため、唯一のオプションは再インストールすることです。
ミラーを次のように交換すると取得できます。
http://old-releases.ubuntu.com/ubuntu/
これにより、18.10→19.04→19.10→20.04に徐々にアップグレードして、最終的にサポートされているLTSリリースに到達できます。しかし、再インストールする方が速く聞こえます。