vim /etc/apt/sources.list 打开文件后选择合适的源（选择一个即可）

#中科大deb http://mirrors./kali kali-rolling main non-free contribdeb-src http://mirrors./kali kali-rolling main non-free contrib#阿里云deb /kali kali-rolling main non-free contribdeb-src /kali kali-rolling main non-free contrib#清华大学deb http://mirrors.tuna./kali kali-rolling main contrib non-freedeb-src https://mirrors.tuna./kali kali-rolling main contrib non-free#163deb /debian wheezy main non-free contribdeb-src /debian wheezy main non-free contribdeb /debian wheezy-proposed-updates main non-free contribdeb-src /debian wheezy-proposed-updates main non-free contribdeb-src /debian-security wheezy/updates main non-free contrib#东软大学deb http://mirrors./kali kali-rolling/main non-free contribdeb-src http://mirrors./kali kali-rolling/main non-free contrib#官方源deb /kali kali-rolling main non-free contribdeb-src /kali kali-rolling main non-free contrib

保存后执行命令

apt-get update -y

yum源过多可能会导致的问题

yum 源的作用，可以理解为解决依赖关系的同时可以提高下载速度，所以我们只需要下载一两个就可以了，推荐下载靠近自己地区的 yum 源。

当导入公钥后依旧下载失败

最后原因就是因为 yum 源问题导致的，之后删除 yum 源后就可以下载了