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socket(2)

socket - create an endpoint for communication

       #include <sys/socket.h>

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

domain(protocol family)

The domain argument specifies a communication domain; this selects the protocol family which will be used for communication. These families are defined in <sys/socket.h>. The formats currently understood by the Linux kernel include:
AF_UNIX Local communication unix(7)
AF_INET IPv4 Internet protocols ip(7)
AF_INET6 IPv6 Internet protocols ipv6(7)

Further details of the above address families, as well as information on several other address families, can be found in address_families(7).

NOTE:

AF*** 中的AF 是**address family**的缩写。

思考: **address family**的含义是什么？

看了 AF_INET ip(7)、AF_INET6 ipv6(7)，我的想法是: 地址。

type

The socket has the indicated type, which specifies the communication semantics. Currently defined types are:

SOCK_STREAM

TCP

SOCK_DGRAM

UDP

SOCK_SEQPACKET

SOCK_RAW

protocol

The protocol specifies a particular protocol to be used with the socket.

Normally only a single protocol exists to support a particular socket type within a given protocol family, in which case protocol can be specified as 0.

NOTE:

一一对应关系

However, it is possible that many protocols may exist, in which case a particular protocol must be specified in this manner. The protocol number to use is specific to the “communication domain” in which communication is to take place; see protocols(5). See getprotoent(3) on how to map protocol name strings to protocol numbers.

Sockets of type SOCK_STREAM

connect(2)

read(2) recv(2)

write(2) send(2)

Out-of-band data

Out-of-band data may also be transmitted as described in send(2) and received as described in recv(2).

SO_KEEPALIVE

When SO_KEEPALIVE is enabled on the socket the protocol checks in a protocol-specific manner if the other end is still alive.

SIGPIPE signal

A SIGPIPE signal is raised if a process sends or receives on a broken stream; this causes naive processes, which do not handle the signal, to exit.

NOTE:

一般，对于这个signal，都是 ，比如SIG_IGN

tag-Redis Signal Handle-signal disposition-signal(SIGPIPE, SIG_IGN)

Sockets of type SOCK_SEQPACKET

SOCK_SEQPACKET sockets employ the same system calls as SOCK_STREAM sockets. The only difference is that read(2) calls will return only the amount of data requested, and any data remaining in the arriving packet will be discarded. Also all message boundaries in incoming datagrams are preserved.

Sockets of type SOCK_DGRAM and SOCK_RAW

sendto(2)

recvfrom(2)

Socket signals

An fcntl(2) F_SETOWN operation can be used to specify a process or process group to receive a SIGURG signal when the out-of-band data arrives or SIGPIPE signal when a SOCK_STREAM connection breaks unexpectedly. This operation may also be used to set the process or process group that receives the I/O and asynchronous notification of I/O events via SIGIO. Using F_SETOWN is equivalent to an ioctl(2) call with the FIOSETOWN or SIOCSPGRP argument.

Operation of sockets

The operation of sockets is controlled by socket level options. These options are defined in . The functions setsockopt(2) and getsockopt(2) are used to set and get options.