環境：
Ubuntu 18.04 64位
問題：
安裝 screen出現 E: Unable to locate package screen
root@iZ2ze779uwgmvbnddt0i1eZ:~#?apt-get?install?screen Reading?package?lists... DoneBuilding?dependency?treeReading?state?information... DoneE:?Unable?to?locate?package?screen
解決：
執行命令
apt-get update