I do some group permission changes on the CentOS server, And then need restart all services. How can I restart all services safely without rebooting?
You could switch to single user mode as SHW suggested and then back again. But for CentOS server you should do it this way:
init 1; init 3
Since the first command will disable your network, you should pass the second one on the same line. Otherwise you will not be able to connect to your server using SSH.