修改配置文件：vim /etc/apt/sources.list
官方源
deb-src http://http.kali.org/kali/ kali-rolling main non-free contrib
deb http://http.kali.org/kali kali-rolling main non-free contrib
中科大源
deb http://mirrors.utsc.edu.cn/kali kali-rolling main non-free contrib
阿里云kali源
deb http://mirrors.aliyun.com/kali sana main non-free contrib
deb http://mirrors.aliyun.com/kali-security sana/updates main contrib non-free
清华更新源
deb http://mirrors.tuna.tsinghua.edu.cn/kali kali-rolling main non-free contrib
deb-src http://mirrors.tuna.tsinghua.edu.cn/kali kali-rolling main non-free contrib
直接去官网找更新源，如阿里云https://developer.aliyun.com/mirror/
apt-get update ：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。
apt-get upgrade：更新了apt的资源列表，没有真正的对系统执行更新。如果需要，要使用apt-get upgrade来更新。
apt-get dist-upgrade：更新bai所有的软件。
apt-get clean：把已安装的软件包的安装包也删除掉。