树莓派ubuntu20.10系统切换国内源
网上有很多关于国内源切换的信息, 不管是阿里源，清华源，还是其他源，需要注意的是将源链接中的ubuntu切换成ubuntu-ports
#aliyun
deb http://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse