琼杰笔记参考:
一、Ubuntu更换阿里云软件源
1. 备份
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2.修改
sudo vim /etc/apt/sources.list
将source.list文件内容替换成下面阿里云的
deb http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
或中科大源：
deb http://mirrors.ustc.edu.cn/ubuntu/ xenial main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-security main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-security main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse
或清华大学源：
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main multiverse restricted universe deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main multiverse restricted universe deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-proposed main multiverse restricted universe deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main multiverse restricted universe deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main multiverse restricted universe deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main multiverse restricted universe deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main multiverse restricted universe deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-proposed main multiverse restricted universe deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main multiverse restricted universe deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main multiverse restricted universe
3. 更新
sudo apt-get update
二、ubuntu16.04下载地址：
中科大源
http://mirrors.ustc.edu.cn/ubuntu-releases/16.04/
阿里云开源镜像站
http://mirrors.aliyun.com/ubuntu-releases/16.04/
兰州大学开源镜像站
http://mirror.lzu.edu.cn/ubuntu-releases/16.04/
北京理工大学开源
http://mirror.bit.edu.cn/ubuntu-releases/16.04/
浙江大学
http://mirrors.zju.edu.cn/ubuntu-releases/16.04/
三、apt-get update和apt-get upgrade命令的区别
1.更新软件列表
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。我们在软件包管理器里看到的软件列表，都是通过update命令更新的。
2.更新软件
sudo apt-get upgrade
这个命令，会把本地已安装的软件，与刚下载的软件列表里对应软件进行对比，如果发现已安装的软件版本太低，就会提示你更新。
3.差别
update
update 是同步 /etc/apt/sources.list 和 /etc/apt/sources.list.d 中列出的源的索引，这样才能获取到最新的软件包。
upgrade
upgrade 是升级已安装的所有软件包，升级之后的版本就是本地索引里的，因此，在执行 upgrade 之前一定要执行 update, 这样安装的才是最新的版本
四、用户管理
1.密码设置
echo -e 'password\npassword' | passwd username
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