How to check open ports on CentOS Linux

1. First install nmap and lsof. #yum install nmap && yum install lsof
2. You can use these comands:

#lsof -i
#lsof -n -P | grep 1723 //1723 anyport
#lsof -i tcp

#nmap -sT -O localhost
#nmap -sU localhost