I encountered this problem once before, but I encountered it today and forgot how to deal with it before, so I recorded it for my own convenience. The CentOS 6 series is an older system. Nowadays, 7 series is commonly used, and many use 8. However, there are still a few users who still insist on 6 series. This article mainly focuses on station cluster servers. Machines with one or two or several IPs are also suitable. Don't encounter this problem.