synaptic 在尝试更新时给出错误，因此我尝试在命令行中运行 sudo apt update，但结果如下：
Hit:1 https://download.mono-project.com/repo/ubuntu stable-focal InRelease
Hit:2 https://www.mirrorservice.org/sites/archive.ubuntu.com/ubuntu focal InRelease
Hit:3 https://packages.microsoft.com/repos/ms-teams stable InRelease
Hit:4 https://www.mirrorservice.org/sites/archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:5 https://www.mirrorservice.org/sites/archive.ubuntu.com/ubuntu focal-backports InRelease
Err:6 https://security.ubuntu.com/ubuntu focal-security InRelease
Could not connect to security.ubuntu.com:443 (91.189.88.142). - connect (111: Connection refused) Could not connect to security.ubuntu.com:443 (91.189.88.152). - connect (111: Connection refused) Could not connect to security.ubuntu.com:443 (91.189.91.38). - connect (111: Connection refused) Could not connect to security.ubuntu.com:443 (91.189.91.39). - connect (111: Connection refused)
Hit:7 https://repo.skype.com/deb stable InRelease
Ign:8 https://dl.google.com/linux/earth/deb stable InRelease
Hit:9 https://dl.google.com/linux/chrome/deb stable InRelease
Hit:10 https://dl.google.com/linux/earth/deb stable Release
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up-to-date.
N: Skipping acquisition of configured file 'main/binary-i386/Packages', as repository 'https://download.mono-project.com/repo/ubuntu stable-focal InRelease' doesn't support architecture 'i386'
N: Skipping acquisition of configured file 'main/binary-i386/Packages', as repository 'https://dl.google.com/linux/chrome/deb stable InRelease' doesn't support architecture 'i386'
N: Skipping acquisition of configured file 'main/binary-i386/Packages', as repository 'https://dl.google.com/linux/earth/deb stable InRelease' doesn't support architecture 'i386'
W: Failed to fetch https://security.ubuntu.com/ubuntu/dists/focal-security/InRelease Could not connect to security.ubuntu.com:443 (91.189.88.142). - connect (111: Connection refused) Could not connect to security.ubuntu.com:443 (91.189.88.152). - connect (111: Connection refused) Could not connect to security.ubuntu.com:443 (91.189.91.38). - connect (111: Connection refused) Could not connect to security.ubuntu.com:443 (91.189.91.39). - connect (111: Connection refused)
W: Some index files failed to download. They have been ignored, or old ones used instead.
我注意到有些人遇到了类似的问题，通过禁用 IPv6 解决了这个问题，但这是在我禁用 IPv6 之后发生的（以前也出现过有关 IPv6 地址的错误）。我检查了防火墙和 DNS 日志，对 security.ubuntu.com 的请求似乎没有被任何东西阻止。
答案1
检查一下关联一次。尝试一下那里显示的方法后，你会很高兴的（：