我试图使用 rvm install "ruby-2.7.0" 在 ubuntu 上安装 ruby。我正在遵循关于这个问题 https://askubuntu.com/questions/91543/apt-get-update-fails-to-fetch-files-temporary-failure-resolving-error 的说明，但我仍然面临这个问题。我怎样才能解决这个问题。
Err:1 http://security.ubuntu.com/ubuntu focal-security InRelease
Temporary failure resolving 'security.ubuntu.com'
Err:2 http://archive.ubuntu.com/ubuntu focal InRelease
Temporary failure resolving 'archive.ubuntu.com'
Err:3 http://archive.ubuntu.com/ubuntu focal-updates InRelease
Temporary failure resolving 'archive.ubuntu.com'
Err:4 http://archive.ubuntu.com/ubuntu focal-backports InRelease
Temporary failure resolving 'archive.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal/InRelease Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal-updates/InRelease Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/focal-backports/InRelease Temporary failure resolving 'archive.ubuntu.com'
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/focal-security/InRelease Temporary failure resolving 'security.ubuntu.com'
W: Some index files failed to download. They have been ignored, or old ones used instead.
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
ubuntu-advantage-tools
The following packages will be upgraded:
initramfs-tools initramfs-tools-bin initramfs-tools-core libssl1.1 openssl sosreport
6 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
Need to get 2252 kB of archives.
After this operation, 4096 B of additional disk space will be used.
Do you want to continue? [Y/n] n