Networking

Address family

AF_UNIX , AF_INET6 , AF_NETLINK , AF_TIPC , AF_CAN , AF_BLUETOOTH , AF_PACKET , AF_RDS,  AF_INET

firewalld

Checking port is open

nmap localhost -p [port]

bash -c "</dev/tcp/127.0.0.1/[port]" && echo "Port is open" || echo "Port is closed"

SO_REUSEPORT

https://lwn.net/Articles/542629/

int s = socket(domain, socktype, 0);

int opt = 1;

setsockopt(s, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt));