1. 查找ubuntu的版本
sudo lsb_release -a
2. 写入阿里云的源
去阿里云查看是否支持当前版本的Codenameubuntu-dists安装包下载_开源镜像站-阿里云 (aliyun.com)
sudo gedit /etc/apt/sources.list
进入后写入下面源信息：
deb http://mirrors.aliyun.com/ubuntu/ $Codename main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/$Codename-backports main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ $Codename-proposed main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ $Codename-security main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/$Codename-updates main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename-backports main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename-proposed main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename-security main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ $Codename-updates main multiverse restricted universe
其中，$Codename换成自己版本的Codename.保存退出
3. 更新
sudo apt-get update
sudo apt-get upgrade
-----------------------------------后面更新---------------------------- 过了一段时间后，发现ubuntu软件源再次失效了，需要重新更新：
在里面选择Ubuntu对应的版本，复制下面的软件源去替换sources.list内容，重新更新即可
