ubuntu 16.04 sudo apt-get update 报错:下列签名无效: KEYEXPIRED 1538166745 KEYEXPIRED 1538166745 解决方法
ubuntu16.04更新报错:sudoapt-getupdate命中:1http://mirrors.aliyun.com/ubuntuxenialInRelease命中:2http://mirrors.aliyun.com/ubuntuxenial-securityInRelease命中:3http://mirrors.aliyun.com/ubuntuxenial-updatesInRele