sudo apt update在更新源时报错 Clearsigned file isn’t valid, got ‘NOSPLIT’ (does the network require authentication?)。
换中科大的源解决，其余源无法解决。
如要用于其他版本，把 jammy 换成其他版本代号即可: 22.04：jammy；20.04：focal；18.04：bionic；16.04：xenial；14.04：trusty。
# 默认注释了源码仓库，如有需要可自行取消注释
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy-security main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy-updates main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy-backports main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy-backports main restricted universe multiverse