1.sudo gedit /etc/apt/sources.list
源列表里面放置的一行行网址，在这个文件里加入或者注释（加#）掉一些源后，保存则源列表里指向的软件就会增加或减少一部分。
2. sudo apt-get update
这个命令，会访问源列表里的每个网址，并读取软件列表，然后保存在本地电脑。软件包管理器里看到的软件列表，都是通过update命令更新的。
3. sudo apt-get upgrate
这个命令，对比源列表网址应用版本和本地应用版本。如果源列表中更新，则更新本地版本。
@https://www.cnblogs.com/lixiangfu/p/11220493.html
如果遇到：sudo apt-get update 更新很慢的时候，可以修改sources.list 中的源。
例如，阿里源的网址：@https://developer.aliyun.com/mirror/ubuntu
图形界面配置
新手推荐使用图形界面配置： 系统设置 -> 软件和更新 选择下载服务器 -> "mirrors.aliyun.com"
手动更改
用你熟悉的编辑器打开：
/etc/apt/sources.list
替换默认的
http://archive.ubuntu.com/
为
mirrors.aliyun.com
以Ubuntu 14.04.5 LTS为例，最后的效果如下：
deb https://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
## Not recommended
# deb https://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
# deb-src https://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
ubuntu 16.04 配置如下
deb http://mirrors.aliyun.com/ubuntu/ xenial main
deb-src http://mirrors.aliyun.com/ubuntu/ xenial main
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main
deb http://mirrors.aliyun.com/ubuntu/ xenial universe
deb-src http://mirrors.aliyun.com/ubuntu/ xenial universe
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates universe
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates universe
deb http://mirrors.aliyun.com/ubuntu/ xenial-security main
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main
deb http://mirrors.aliyun.com/ubuntu/ xenial-security universe
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security universe
ubuntu 18.04(bionic) 配置如下
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe mul