I want to know the right command to type from a bash shell so that i can
1) Check the version of my cent os
2) Check all the open ports (tcp and udp) on my machine
3) Open a specific port say port 3306 so that a telnet request from a remote machiene can be accepted
4) Disable the effect of 3 above in case I want to
Thanks in anticiaption of your kind responses to the questions above.