问题
Err:2 http://cn.archive.ubuntu.com/ubuntu focal/universe amd64 libflann-dev amd64 1.9.1+dfsg-9build1 Connection failed [IP: 91.189.91.38 80] E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/f/flann/libflann1.9_1.9.1+dfsg-9build1_amd64.deb Connection failed [IP: 91.189.91.38 80] E: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/pool/universe/f/flann/libflann-dev_1.9.1+dfsg-9build1_amd64.deb Connection failed [IP: 91.189.91.38 80] E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
解决方法
https://mirror.tuna.tsinghua.edu.cn/help/ubuntu/ sudo vi /etc/apt/sources.list sudo apt-get update sudo apt-get install libflann1.9 libflann-dev
参考
1.
https://mirror.tuna.tsinghua.edu.cn/help/ubuntu/