Linux Socket System

A socket is a file descriptor representing one endpoint of a communications channel. Programs create one with socket(2), then usually bind or connect it and use read(2)/write(2) or send(2)/recv(2).

int sockfd = socket(int domain, int type, int protocol);

The domain selects an address family such as AF_INET, AF_INET6, AF_UNIX, or AF_NETLINK. The type selects a semantic such as SOCK_STREAM, SOCK_DGRAM, or SOCK_SEQPACKET; the protocol normally selects a concrete protocol within that combination, or 0 selects the default.

Common Socket Families #