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 -