当我跑步时，sudo apt-get update这是我得到的东西
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
我现在无法安装任何东西
答案1
Ubuntu 18.10（Cosmic Cuttlefish）于 2019 年 7 月终止生命，并已从 Ubuntu 存档中删除。到目前为止，它将存在几个严重的安全问题，您应该尽快升级到受支持的版本。
不幸的是，Ubuntu 不支持从非 LTS 版本（如 18.10）升级到下一个 LTS 20.04，因此您唯一的选择可能是重新安装。
您可以通过将镜子替换为以下内容来勉强维持：
http://old-releases.ubuntu.com/ubuntu/
这可以让您逐步升级 18.10→19.04→19.10→20.04，最终获得受支持的 LTS 版本。不过，重新安装听起来更快。