Ubuntu 系统中,执行apt update超时，需要进行换源，apt软件源文件地址为：/etc/apt/sources.list ，主要步骤如下：

1、备份原来的源，将以前的源备份一下，以防以后可以用的。

$ sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak

2、打开 /etc/apt/sources.list 文件，在前面添加如下条目，并保存。

$ sudo vim /etc/apt/sources.list（可将 vim 更换为自己熟悉的编辑器）

添加阿里源

# 阿里云源 deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse ##########proposed表示测试版本源，不建议启用 #deb http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse ##########源码 deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse ##########测试版源 #deb-src http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse

# 清华大学源 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricted universe multiverse deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricted universe multiverse deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse #############测试版源 #deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse #############源码 deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricted universe multiverse deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricted universe multiverse deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse ##############proposed表示测试版源，不建议启用 #deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse

3、更新

更新源 $ sudo apt-get update

如出现依赖问题，解决方式如下：$ sudo apt-get -f install

更新软件：$ sudo apt-get upgrade