Use the command systemctl start iptables    firewall is enabled, the following error.

Failed to start iptables.service: Unit iptables.service failed to load: No such file or directory.

Search the next error because there is seemingly installed iptables-services.

使用 yum install iptables-services 报错  xxxxx   [Errno 256] No more mirrors to try.

So found a solution to try, execute the following command

1:  yum Clean All    completed

2: yum makecache   the following error:

[Errno 14] curl#37 - "Couldn't open file /mnt/repodata/repomd.xml

Because of this error, check for nearly two hours in various ways no solution, and finally found a closer look at the error message. Path request is /mnt/repodata/repomd.xml. And my redhat system disk loading path is / mnt / cdrom / repodata /

There may be modified before the fstab. 

When fstab file of information being given.

Use command vim / etc / fstab modify fstab file inster insert mode key, completion and modified by ESC , enter : wq Save

The revised fstab file:

After modifying fstab file, execute  umount -a  dismount  ,    execute  mount -a to remount.

Re-run  yum makecache success. 

Because of this problem toss me two hours helpless want to reinstall redhat up. So easy to solve the routing problem, actually search to search to search for two hours. After the encounter the error must seriously look at the error message.