various methods to find and list open ports

linux open ports

# tcp ports and services

egrep -w '(80|22|443)/tcp' /etc/services

# netstat list of open ports 

sudo netstat -tulp | grep LISTEN

# -t – List all TCP ports on Linux
# -u – List all UDP ports on Linux
# -l – Show only listening sockets/ports
# -p – Show process names (PID) using sockets/ports in Linux
# -n – Do not try to resolve service names (speed up option) using /etc/resolv.conf file

sudo ss -tulpn

sudo lsof -i