libGL.so.1: cannot open shared object file: No such file or directory

[Problem]
When installing mmcv, it prompts: ImportError: libGL.so.1: cannot open shared object file: No such file or directory.
This should be caused by the installation of opencv-python.

[Solution]
https://github.com/open-mmlab/mmsegmentation/issues/1327
Install libsm6 libxext6 ffmpeg these dependencies:

sudo apt-get update
sudo apt-get install libsm6 libxext6 ffmpeg -y