Creating sockets

Sockets are file descriptors returned by the C socket function.

#include <sys/socket.h>

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

On error socket returns -1 and errno is set to one of the following:

• EAFNOSUPPORT
• EMFILE
• ENFILE
• EPROTONOSUPPORT
• EPROTOTYPE
• EACCESS
• ENOBUFS
• ENOMEM

On success, the function returns the fd of the new socket.

Socket domains

The domain specifies the address family. Valid address families are implementation defined.

Most used

• AF_UNIX or AF_LOCAL
• AF_INET
• AF_INET6

Rarely used

• AF_X25
• AF_AX25
• AF_IPX
• AF_APPLETALK
• AF_DECnet
• AF_KEY
• AF_NETLINK
• AF_PACKET
• AF_RDS
• AF_PPPOX
• AF_LLC
• AF_IB
• AF_MPLS
• AF_CAN
• AF_TIPC
• AF_BLUETOOTH
• AF_ALG
• AF_VSOCK
• AF_KCM
• AF_XDP

Socket types

These are valid socket types:

• SOCK_STREAM: sequences, relaiable, bidirectional, connection-mode byte stream.
• SOCK_DGRAM: connectionsless-mode unrelaiable messages of fixed max length.
• SOCK_SEQPACKET:
• SOCK_RAW:
• SOCK_RDM:
• SOCK_PACKET:
• SOCK_NONBLOCK:
• SOCK_CLOEXEC: