我想做发布升级，但我首先需要 apt-get 升级。它无法获取各种包，并且失败。添加免费的 Ubuntu Pro 并不能修复该错误。
我运行的是 18.04：
# cat /etc/issue
Ubuntu 18.04.6 LTS \n \l
do-release-upgrade 抱怨我需要先 apt-get 升级
# do-release-upgrade
Checking for a new Ubuntu release
Please install all available updates for your release before upgrading.
为了彻底，首先运行更新：
# apt-get update
... works ok
问题是这样的：升级失败并出现 401 错误：
# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
grub-common grub-pc grub-pc-bin grub2-common landscape-common linux-generic
linux-headers-generic linux-image-generic …