Содержание
Linux can create socket
NAME
socket - create an endpoint for communication
SYNOPSIS
#include /* See NOTES */ #include int socket(int domain, int type, int protocol);
DESCRIPTION
socket() creates an endpoint for communication and returns a descriptor. The domain argument specifies a communication domain; this selects the protocol family which will be used for communication. These families are defined in . The currently understood formats include: Name Purpose Man page AF_UNIX, AF_LOCAL Local communication unix(7) AF_INET IPv4 Internet protocols ip(7) AF_INET6 IPv6 Internet protocols ipv6(7) AF_IPX IPX - Novell protocols AF_NETLINK Kernel user interface device netlink(7) AF_X25 ITU-T X.25 / ISO-8208 protocol x25(7) AF_AX25 Amateur radio AX.25 protocol AF_ATMPVC Access to raw ATM PVCs AF_APPLETALK AppleTalk ddp(7) AF_PACKET Low level packet interface packet(7) AF_ALG Interface to kernel crypto API The socket has the indicated type, which specifies the communication semantics. Currently defined types are: SOCK_STREAM Provides sequenced, reliable, two-way, connection-based byte streams. An out-of-band data transmission mechanism may be supported. SOCK_DGRAM Supports datagrams (connectionless, unreliable messages of a fixed maximum length). SOCK_SEQPACKET Provides a sequenced, reliable, two-way connection-based data transmission path for datagrams of fixed maximum length; a consumer is required to read an entire packet with each input system call. SOCK_RAW Provides raw network protocol access. SOCK_RDM Provides a reliable datagram layer that does not guarantee ordering. SOCK_PACKET Obsolete and should not be used in new programs; see packet(7). Some socket types may not be implemented by all protocol families. Since Linux 2.6.27, the type argument serves a second purpose: in addition to specifying a socket type, it may include the bitwise OR of any of the following values, to modify the behavior of socket(): SOCK_NONBLOCK Set the O_NONBLOCK file status flag on the new open file description. Using this flag saves extra calls to fcntl(2) to achieve the same result. SOCK_CLOEXEC Set the close-on-exec (FD_CLOEXEC) flag on the new file descriptor. See the description of the O_CLOEXEC flag in open(2) for reasons why this may be useful. 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. 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 are full-duplex byte streams. They do not preserve record boundaries. A stream socket must be in a connected state before any data may be sent or received on it. A connection to another socket is created with a connect(2) call. Once connected, data may be transferred using read(2) and write(2) calls or some variant of the send(2) and recv(2) calls. When a session has been completed a close(2) may be performed. Out-of-band data may also be transmitted as described in send(2) and received as described in recv(2). The communications protocols which implement a SOCK_STREAM ensure that data is not lost or duplicated. If a piece of data for which the peer protocol has buffer space cannot be successfully transmitted within a reasonable length of time, then the connection is considered to be dead. When SO_KEEPALIVE is enabled on the socket the protocol checks in a protocol-specific manner if the other end is still alive. 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. 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. SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams to correspondents named in sendto(2) calls. Datagrams are generally received with recvfrom(2), which returns the next datagram along with the address of its sender. SOCK_PACKET is an obsolete socket type to receive raw packets directly from the device driver. Use packet(7) instead. 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. When the network signals an error condition to the protocol module (e.g., using a ICMP message for IP) the pending error flag is set for the socket. The next operation on this socket will return the error code of the pending error. For some protocols it is possible to enable a per-socket error queue to retrieve detailed information about the error; see IP_RECVERR in ip(7). 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, respectively.
RETURN VALUE
On success, a file descriptor for the new socket is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EACCES Permission to create a socket of the specified type and/or protocol is denied. EAFNOSUPPORT The implementation does not support the specified address family. EINVAL Unknown protocol, or protocol family not available. EINVAL Invalid flags in type. EMFILE The per-process limit on the number of open file descriptors has been reached. ENFILE The system-wide limit on the total number of open files has been reached. ENOBUFS or ENOMEM Insufficient memory is available. The socket cannot be created until sufficient resources are freed. EPROTONOSUPPORT The protocol type or the specified protocol is not supported within this domain. Other errors may be generated by the underlying protocol modules.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, 4.4BSD. The SOCK_NONBLOCK and SOCK_CLOEXEC flags are Linux-specific. socket() appeared in 4.2BSD. It is generally portable to/from non-BSD systems supporting clones of the BSD socket layer (including System V variants).
NOTES
POSIX.1 does not require the inclusion of , and this header file is not required on Linux. However, some historical (BSD) implementations required this header file, and portable applications are probably wise to include it. The manifest constants used under 4.x BSD for protocol families are PF_UNIX, PF_INET, and so on, while AF_UNIX, AF_INET, and so on are used for address families. However, already the BSD man page promises: "The protocol family generally is the same as the address family", and subsequent standards use AF_* everywhere. The AF_ALG protocol type was added in Linux 2.6.38. More information on this interface is provided with the kernel HTML documentation at https://www.kernel.org/doc/htmldocs/crypto- API/User.html.
EXAMPLE
SEE ALSO
accept(2), bind(2), close(2), connect(2), fcntl(2), getpeername(2), getsockname(2), getsockopt(2), ioctl(2), listen(2), read(2), recv(2), select(2), send(2), shutdown(2), socketpair(2), write(2), getprotoent(3), ip(7), socket(7), tcp(7), udp(7), unix(7) “An Introductory 4.3BSD Interprocess Communication Tutorial” and “BSD Interprocess Communication Tutorial”, reprinted in UNIX Programmer's Supplementary Documents Volume 1.
Linux can create socket
NAME
socket - create a TCP or a UNIX domain socket and connect to stdin/out
SYNOPSIS
socket [ -bcfqrvw ] [ -p command ] [ -B local address ] host port socket [ -bcfqrvw ] [ -p command ] /path socket [ -bcfqrvw ] [ -p command ] [ -B local address ] -s [ -l ] port socket [ -bcfqrvw ] [ -p command ] -s [ -l ] /path
DESCRIPTION
Socket creates an Internet domain TCP or a UNIX domain stream socket and connects it to stdin and stdout. The host argument can be an Internet number in dot-notation (like ``130.149.28.10'') or a domain name. In this case it must be possible to resolve the name to a valid Internet address with gethostbyname(3). The port argument can be a port number or a service name which can be mapped to a port number by getservbyname(3). If an UNIX domain socket is wanted to be created instead of an Internet socket, specify the path instead of an internet (canonical domain named or dot-notated) host. The hostname is treated as a pathname if contains at least a single slash. I.e. if one wants to create or connect to a socket in the current directory, use ./filename to specify the connection point.
OPTIONS
-b (background) The program forks itself into the background, detaches from its controlling tty, closes the file descriptors associated with the tty, and changes its current directory to the root directory. -B (local address) This option specifies which local address to binded to when making a connection. -c (crlf) Linefeed characters (LF) are converted to a Carriage Return Linefeed sequence (CRLF) when written to the socket. CRLF sequences read from the socket are converted to a single LF. -f (fork) When a server connection has been accepted, a separate process is forked to handle the connection in background. -l (loop) (only valid with -s) After a connection has been closed, another connection is accepted. -p (program) The specified command is executed for each connection. Its standard input, standard output, and standard error channels are connected to the socket. Command can be any shell command since it is passed to /bin/sh. -q (quit) The connection is closed when an end-of-file condition occurs on standard input. -r (read only) No data is read from standard input and written to the socket. -s (server) A server socket is created. A hostname argument is not required of Internet sockets, only the port number but a pathname is required for UNIX domain sockets. -v (verbose) Messages about connections etc. are issued to stderr. -w (write only) No data is read from the socket and written to the standard output. -version Socket prints its version ID and terminates. This must be the first argument to have an effect.
EXAMPLES
The command socket -v coma.cs.tu-berlin.de nntp connects to the nntp port (port 119) of coma.cs.tu-berlin.de (130.149.28.10). The command socket -sl 3425 creates a server socket on port 3425 on the local host and waits for a connection. After a connection has been closed, a new connection is accepted. The command socket -wslqvp "echo Socket! " 1938 creates a server socket on port 1938 on the local host and waits for a connection. When a connection is accepted, the string "Socket!" is written to the socket. No data is read from the socket and written to the finger program. The connection is closed when an end- of-file condition at the standard output of the program occurs. Then a new connection is accepted.
DIAGNOSTICS
Lots of diagnostics for failed system calls. unknown host host host's address could not be resolved. Signal signal caught, exiting Socket exits on any signal other than SIGTSTP, SIGCONT, SIGCLD, SIGQUIT. A non-zero exit code is returned if socket terminates due to an error condition or a signal.
SEE ALSO
ip(7), tcp(7), unix(7), accept(2), bind(2), listen(2), connect(2), socket(2), gethostbyname(3), getservbyname(3)
BUGS
socket -p terminates due to a SIGPIPE signal when there is more data from the socket available than the executed program wants to read. Please report any other bugs to the author.
VERSION
This manual page describes Socket-1.1.