sudo apt-get update:
1、Ubuntu 16.04 apt-get update 暂时不能解析域名“us.archive.ubuntu.com”
原因是 dns 没有配置，解决办法是加入 dns 服务器地址(编辑之前记得备份)，比如：
$ vi /etc/resolv.conf
nameserver 202.96.134.133
nameserver 8.8.8.8
nameserver 8.8.4.4
如果提示只读，用 sudo 运行，即 sudo vi /etc/resolv.conf，运行完重启系统解决。
2、Failed to fetch http://ppa.launchpad.net/jonathonf/ffmpeg-4/ubuntu/pool/main/f/ffmpeg/libswresample3_4.1-1~16.04.york0_amd64.deb Connection timed out
opencv:
１、v4l2-ctl --set-fmt-video=width=1920,height=1080,pixelformat=1
v4l2-ctl --set-parm=30
and observe that:
v4l2-ctl -V
os.system("v4l2-ctl --set-fmt-video=width=1920,height=1080,pixelformat=1")
os.system("v4l2-ctl --set-parm=30")
[opencv(via python) on Linux: Set frame width/height][1]
２、Installing OpenCV 3.3.1 failed.
Return Code: 1
Error: libopencv-python libopencv-samples cannot be installed on host. Please manually run following command in terminal to install packages before continuing:
sudo apt install /home/ad/chen/jetson/jetpack_download/libopencv_3.3.1_amd64.deb /home/ad/chen/jetson/jetpack_download/libopencv-dev_3.3.1_amd64.deb /home/ad/chen/jetson/jetpack_download/libopencv-python_3.3.1_amd64.deb /home/ad/chen/jetson/jetpack_download/libopencv-samples_3.3.1_amd64.deb
answer:sudo find / -name "*opencv*" -exec rm -rf {} \;
sudo find /usr/ -name "*opencv*3.4*" -delete
sudo apt remove libopencv*