操作系统：Ubuntu Server 18.04 LTS
Ubuntu每次启动时产生如下motd（message of today）输出
Failed to connect to https://changelogs.ubuntu.com/meta-release-lts. Check your Internet connection or proxy settings // A
可能是网络配置写错了，比如DNS写错了等，也可能是bug。
脚本/etc/update-motd.d/91-release-upgrade运行的同时会简介运行/usr/lib/ubuntu-release-upgrader/release-upgrade-motd，从以下url下载文件meta-release-lts
https://changelogs.ubuntu.com/meta-release-lts
这个文件没有登记bionic的条目，没有Ubuntu 18的记录，但是Ubuntu上的程序没有做出处理，于是产生A行输出到/var/lib/ubuntu-release-upgrader/release-upgrade-available。
通过cat命令看一下这个文件的内容。
root@localghost~# cat /var/lib/ubuntu-release-upgrader/release-upgrade-available Failed to connect to https://changelogs.ubuntu.com/meta-release-lts. Check your Internet connection or proxy settings
（1）移除/var/lib/ubuntu-release-upgrader/release-upgrade-available
root@localghost~#rm /var/lib/ubuntu-release-upgrader/release-upgrade-available
（2）运行/usr/lib/ubuntu-release-upgrader/release-upgrade-motd
root@localghost~#./usr/lib/ubuntu-release-upgrader/release-upgrade-motd
https://askubuntu.com/questions/919441/failed-to-connect-to-http-changelogs-ubuntu-com-meta-release
https://ubuntuforums.org/showthread.php?t=2391641