Restart all services without reboot

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.

Simply execute these two commands:

1. init 1
2. init 5

Init 1 will bring your computer to single user mode, where minimal services are running, and init 5 will being the system back to GUI mode, by restarting all the services