So you have set up a very secured server but still don't you want to cross check if the machine is really secured and your server has not been compromised by anyone. If is always better to regularly scan your system with open ports and list of connected machines.
For this blog I will show you the command to get a list of open ports in any machine
nmap command can be used to do the same. You can download in RedHat machine using yum
# yum install nmap
Once installed verify the package
# rpm -qa | grep nmap
nmap-5.51-2.el6.i686
# nmap <address>
# nmap localhost
Starting Nmap 5.51 ( http://nmap.org ) at 2013-05-03 12:39 IST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.0000080s latency).
Other addresses for localhost (not scanned): 127.0.0.1
Not shown: 981 closed ports
PORT STATE SERVICE
22/tcp open ssh
25/tcp open smtp
80/tcp open http
111/tcp open rpcbind
631/tcp open ipp
1935/tcp open rtmp
3306/tcp open mysql
5222/tcp open xmpp-client
5269/tcp open xmpp-server
5802/tcp open vnc-http-2
5902/tcp open vnc-2
5989/tcp open wbem-https
6002/tcp open X11:2
7070/tcp open realserver
7443/tcp open oracleas-https
7777/tcp open cbt
8443/tcp open https-alt
9090/tcp open zeus-admin
9091/tcp open xmltec-xmlmail
Here as you can see I got a long list of opened ports on my machine.
Go ahead and try the same on your machine.
