尝试升级我的 Ubuntu 时出现以下问题：
$ sudo do-release-upgrade -d
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [819 B]
Get:2 Upgrade tool [1,267 kB]
Fetched 1,268 kB in 0s (0 B/s)
authenticate 'jammy.tar.gz' against 'jammy.tar.gz.gpg'
extracting 'jammy.tar.gz'
Reading cache
Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done
Hit http://us.archive.ubuntu.com/ubuntu focal InRelease
Hit https://repo.nordvpn.com//deb/nordvpn/debian stable InRelease
Get:1 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Get:2 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease [108 kB]
Get:3 http://us.archive.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Fetched 336 kB in 0s (0 B/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
None
Restoring original system state
Aborting
Reading package lists... Done
Building dependency tree
Reading state information... Done
请问有什么想法吗？提前致谢。