After encountering this problem, we refer to no less than ten online tutorials, none of which is effective, including but not limited to:

1. Hang up VPN (it seems that many people finally rely on science to get online, but I still can’t hang it here

2. Modify the upper limit of time parameter: useless, the system has the default maximum value, about one minute, to treat the symptoms but not the root cause

3. Modify the host file: all kinds of addresses of Google and GitHub have been added in, which is useless

4. Hang hot spot: same as 1, useless

For the final solution, please refer to Baidu Post Bar:

sudo apt-get update

sudo apt-get install python-rosdep

  In the second step, there is an error message when installing Python rosdep. It seems that some files were not successfully installed, but in the end, rosdep update succeeded.