The situation is: CentOS 6.7 server cannot connect to the external network normally, and can only be used in the internal network. The “cannot find a valid baseurl for repo” error box pops up frequently. Here’s a screenshot:

As the system is running normally, it does not need to be updated. Therefore, by adjusting the system settings and setting the system to “never check for updates” and “never update”, this error box will not appear in the system. As shown in the figure below: