When installing ROS under Ubuntu 16.04, you will encounter problems when executing the sudo rosdep init step, as shown in the following figure:
Tried many ways, without success.
Later, I referred to the blog https://www.ioiox.com/archives/62.html, and found that it might be blocked, and the address raw.githubusercontent.com could not be connected at all, so I tried this one Method:
1. Query the real IP
through the home page of IPAddress.com, enter raw.githubusercontent.com to query the real IP address
IPAddress.com URL: https://www.ipaddress.com/
The real IP address is as shown above
2. Open the Ubuntu terminal and enter:
sudo gedit /etc/hosts
3. Add in:
199.232.68.133 raw.githubusercontent.com
After saving, continue to execute sudo rosdep init.