“升级期间出现错误” - 如何继续？

Question

我刚刚将 Ubuntu 从 16.04 升级到 18.04，并收到以下消息：

The upgrade has completed but there were errors during the upgrade process. 

To continue please press [ENTER]

没有关于这些错误的进一步信息。按 ENTER 后，我做了：

sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
sudo apt do-release-upgrade

没有错误，我收到消息：

Checking for a new Ubuntu release
There is no development version of an LTS available.
To upgrade to the latest non-LTS develoment release 
set Prompt=normal in /etc/update-manager/release-upgrades.

我担心这个“升级过程中出现错误”的消息，因为我读到升级后，重新启动后可能会出现问题 - 桌面可能不会显示。如何检查升级过程中发生了什么错误以及如何修复这些错误？