What does apt update do?
"apt update" updates the package sources list with the latest versions of the packages in the repositories
What does apt upgrade do then?
"apt upgrade" compares the version of all the packages currently installed on the system with the ones in the list we fetched through apt update and upgrades all of them to their latest versions.
我用openwrt, v2ray 最高version 只能去到4.42.2-1正常 run 到, 之後v2ray新d 嘅version ( e.g. 4.43.x, 4.44.x, 4.45.x) 出 error message 根本行唔到