进入/etc/apt目录下，会有一个sources.list文件，先把他备份一份sudo cp sources.list sources.list.old 然后打开sources.list
sudo vim sources.list
把里边内容改为下边内容（其他的Linux版本可以参考阿里源【阿里镜像源】）
deb http://mirrors.aliyun.com/ubuntu/ eoan main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-backports main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-proposed main restricted universe multiverse
保存退出，然后检查更新源
sudo apt-get update
sudo apt-get upgrade
待更新完成即完成。
