公司生产环境相关的Ubuntu VM需要升级到最新的LTS版本，期间遇到了两个奇怪的小问题

1.Can not run the upgrade
This usually is caused by a system where /tmp mounted noexec. Please remount without noexec and run the upgrade again.

tmp被以禁止执行任何二进制包和脚本的形式挂载，用命令sudo mount -o remount,exec /tmp 即可解决

2.ppa.launchpad.net连不上

因为是生产环境VM，所以长期断网，导致公钥无法及时更新，手动从Keyserver下载公钥即可解决

报错形式为The following signatures couldn't be verified because the public key is not available: NO_PUBKEY XXXXXXXXXXXXX

sudo gpg --keyserver keyserver.ubuntu.com --recv XXXXXXXXXXXXX

sudo gpg --export --armor XXXXXXXXXXXXX | sudo apt-key add -