我有一个网站托管在 Ubuntu 18.10 上，我无法安装任何东西。起初一切都正常（几周前我第一次生成这个 VPS 时），但现在我总是收到错误
me@cdad:/etc/php/7.2/mods-available$ sudo apt-get install php7.2-mbstring
...
Ign:1 http://us.archive.ubuntu.com/ubuntu cosmic-updates/universe amd64 php7.2-mbstring amd64 7.2.19-0ubuntu0.18.10.1
Err:1 http://security.ubuntu.com/ubuntu cosmic-updates/universe amd64 php7.2-mbstring amd64 7.2.19-0ubuntu0.18.10.1
404 Not Found [IP: 91.189.91.38 80]
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/universe/p/php7.2/php7.2-mbstring_7.2.19-0ubuntu0.18.10.1_amd64.deb 404 Not Found [IP: 91.189.91.38 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
我尝试了很多事情，例如运行sudo apt-get update --allow-unauthenticated或[trusted=yes]添加/etc/apt/sources.list。
我还检查了硬盘上是否有足够的空间，以及所有权限是否正常工作。我禁用了它，ufw但现在没有解决方案了……
任何帮助都将非常感谢，我甚至在今天早上尝试了版本升级，因为系统建议这样做，但也失败了。
New release '19.10' available.
Run 'do-release-upgrade' to upgrade to it.
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For upgrade information, please visit:
http://www.ubuntu.com/releaseendoflife
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Fetched 1,331 kB in 0s (0 B/s)
authenticate 'eoan.tar.gz' against 'eoan.tar.gz.gpg'
extracting 'eoan.tar.gz'
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Can not upgrade
An upgrade from 'cosmic' to 'eoan' is not supported with this tool.