sudo apt reinstall ubuntu-release-upgrader-core
cat /var/lib/ubuntu-release-upgrader/release-upgrade-available
rm /var/lib/ubuntu-release-upgrader/release-upgrade-available
rm /usr/lib/ubuntu-release-upgrader/release-upgrade-motd
cat /var/lib/ubuntu-release-upgrader/release-upgrade-available
连接成功，并且没有报错信息