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socket (4)
  • socket (2) ( FreeBSD man: Системные вызовы )
  • socket (2) ( Русские man: Системные вызовы )
  • socket (2) ( Linux man: Системные вызовы )
  • socket (3) ( Solaris man: Библиотечные вызовы )
  • socket (3) ( POSIX man: Библиотечные вызовы )
  • >> socket (4) ( Linux man: Специальные файлы /dev/* )
  • socket (7) ( Русские man: Макропакеты и соглашения )
  • socket (7) ( Linux man: Макропакеты и соглашения )
  • socket (9) ( FreeBSD man: Ядро )
  • Ключ socket обнаружен в базе ключевых слов.
  •  

    NAME

    socket - Linux socket interface
     
    

    SYNOPSIS

    #include <sys/socket.h>
    mysocket = socket(int socket_family, int socket_type, int protocol);
       

    DESCRIPTION

    This man page describes the BSD compatible Linux networking sockets layer. The sockets layer is the uniform interface between the user process and the in kernel network protocol stacks. The protocol modules are grouped into protocol families like PF_INET, PF_IPX, PF_PACKET and socket types like SOCK_RAW or SOCK_DGRAM. See socket(2) for more information.

     

    SOCKET LAYER FUNCTIONS

    These functions are used by the user process to send or receive packets and to do other socket operations. For more information see their man pages.

    socket(2) creates a socket, connect(2) connects a socket to a foreign socket address, the bind(2) function binds a socket to a local socket address, listen(2) tells the socket that new connections will be accepted, and accept(2) is used to get a new socket with the new connection. socketpair(2) returns two connected anonymous sockets.

    send(2), sendto(2), and sendmsg(2) send data over a socket, and recv(2), recvfrom(2), recvmsg(2) receive data from a socket. poll(2) and select(2) wait for arriving data or a readiness to send data. In addition, the standard I/O operations like write(2), writev(2), read(2), and readv(2) can be used to read and write data.

    getsockname(2) returns the local socket address and getpeername(2) returns the foreign socket address. getsockopt(2) and setsockopt(2) are used to set or get socket layer or protocol options. ioctl(2) can be used to set or read some other options.

    close(2) is used to close a socket. shutdown(2) closes parts of a full duplex socket connection.

    Seeking is not supported on sockets.  

    SOCKET OPTIONS

    These socket options can be set by using setsockopt(2) and read with getsockopt(2) with the socket level set to SOL_SOCKET for all sockets..
    SO_KEEPALIVE
    Enable sending of keep-alive messages on connection-oriented sockets. Expects a integer boolean flag.
    SO_OOBINLINE
    If this option is enabled, out-of-band data is directly placed into the receive data stream. Otherwise out-of-band data is only passed when the MSG_OOB flag is set during receiving.
    SO_RCVLOWAT and SO_SNDLOWAT
    Specify the minimum number of bytes in the buffer until the socket layer will pass the data to the protocol (SO_SNDLOWAT) or the user on receiving (SO_RCVLOWAT). These two values are not changeable in Linux and their argument size is always fixed to 1 byte. Getsockopt is able to read them; setsockopt will always return ENOPROTOOPT.
    SO_RCVTIME0 and SO_SNDTIME0
    Specify the sending or receiving timeouts until reporting an error. They are fixed to a protocol specific setting in Linux and cannot be read or written. They can be easily emulated using alarm(2).
    SO_BSDCOMPAT
    Enable BSD bug-to-bug compatibility. This is used only by the UDP protocol module and scheduled to be removed in future. If enabled ICMP errors received for a UDP socket will not be passed to the user program. Linux 2.0 enabled BSD bug-to-bug compatibility options (random header changing, skipping of the broadcast flag) for the raw sockets with this option too, but that has been removed with Linux 2.2. It is better to fix the user programs than to enable this flag.
    SO_PASSCRED
    Enable or disable the receiving of the SCM_CREDENTIALS control message. For more information see unix(4).
    SO_PEERCRED
    Return the credentials of the foreign process connected to this socket. Only useful for PF_UNIX sockets; see unix(4). Argument is a ucred structure. Only valid as a getsockopt.
    SO_BINDTODEVICE
    Bind this socket to a particular device like lqeth0rq, as specified in the passed interface name. If the name is an empty string or the option length is zero, the socket is not bound. The passed option is a variable-length interface name string (with the maximum size of IFNAMSIZ). If a socket is bound to an interface, only packets received from the bound interface are passed to the user.
    SO_DEBUG
    Enable socket debugging. Only allowed for processes with effective user id 0.
    SO_REUSEADDR
    Indicates that the rules used in validating addresses supplied in a bind(2) call should allow reuse of local addresses. For PF_INET sockets this means that a socket may bind, except when there is an active listening socket bound to the address. When the listening socket is bound to INADDR_ANY with a specific port then it is not possible to bind to this port for any local address.
    SO_TYPE
    Gets the socket type as an integer (like SOCK_STREAM). Can be only read with getsockopt.
    SO_DONTROUTE
    Bypass the routing table and send directly to the interface specified by the network part of the destination address. The same effect can be achieved by setting the MSG_DONTROUTE flag on a socket send operation. Expects an integer boolean flag.
    SO_BROADCAST
    Set or get the broadcast flag. When enabled, datagram sockets receive packets sent to a broadcast address and they are allowed to send packets to a broadcast address. This option has no effect on stream-oriented sockets.
    SO_SNDBUF
    Sets or gets the maximum socket send buffer in bytes. Default value is set by the wmem_default sysctl. The maximum allowed value is set by the wmem_max sysctl.
    SO_RCVBUF
    Sets or gets the maximum socket receive buffer in bytes. Default value is set by the rmem_default sysctl. The maximum allowed value is set by the rmem_max sysctl.
    SO_LINGER
    Sets or gets the SO_LINGER option. The argument is a linger structure.

    
    struct linger {
        int             l_onoff;    /* linger active */
        int             l_linger;   /* how long to linger for in seconds */
    };
    
    
    When enabled, a close(2) or shutdown(2) will not return until all queued messages for the socket have been successfully sent or the linger timeout has been reached. Otherwise, the call returns immediately and the closing is done in the background. When the socket is closed as part of exit(2), it always lingers in the background.
    SO_PRIORITY
    Set the protocol-defined priority for all packets to be sent on this socket. Linux uses this value to order the networking queues: packets with a higher priority may be processed first depending on the selected device queueing discipline. For ip(4), this also sets the IP type-of-service (TOS) field for outgoing packets.
    SO_ERROR
    Get and clear the pending socket error. Only valid as a getsockopt. Expects an integer.
     

    SIGNALS

    On connection-oriented sockets, SIGPIPE is sent when a disconnection request has been received or the process writes to a socket that has been locally shut down. In some cases, SIGPIPE is only send when the SO_KEEPALIVE option is enabled.

    When requested with the FIOCSETOWN or SIOCSPGRP ioctl, SIGIO is sent when an I/O event occurs. Valid I/O events include:

    -
    New data arrived. The socket send buffer has enough room to queue new data.
    -
    A new connection request has completed (only for connection-oriented protocols).
    -
    A disconnection request has been initiated.
    -
    A connection is broken (only for connection-oriented protocols). SIGPIPE might be sent also in this case.
    -
    An asynchronous error occured. The other end has shut down one direction.

    In some situations (multiple processes or the kernel sending data to a single socket) the condition that caused the SIGIO might already have disappeared when the SIGIO is processed by the user process. When this happens the user process should just wait again because Linux guarantees to resend a new SIGIO later.  

    SYSCTLS

    The core socket networking sysctls can be accessed using the /proc/sys/net/core/* files or with the sysctl(2) interface.
    rmem_default
    contains the default setting in bytes of the socket receive buffer.
    rmem_max
    contains the maximum receive socket buffer size in bytes a user can set using the SO_RCVBUF socket option.
    wmem_default
    contains the default setting in bytes of the socket send buffer.
    wmem_max
    contains the maximum send socket buffer size in bytes a user can set using the SO_SNDBUF socket option.
    message_cost
    and message_burst configure the token bucket filter used to load limit warning messages caused by external network events.
    netdev_max_backlog
    Maximum number of packets in a input queue.
     

    BUGS

    The CONFIG_FILTER socket options SO_ATTACH_FILTER and SO_DETACH_FILTER are not documented.  

    VERSIONS

    SO_BINDTODEVICE was introduced in Linux 2.0.30. SO_PASSCRED is new in Linux 2.2. The sysctls are new in Linux 2.2.  

    SEE ALSO

    socket(2), ip(4), setsockopt(2), getsockopt(2), packet(4), ddp(4)


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    SOCKET LAYER FUNCTIONS
    SOCKET OPTIONS
    SIGNALS
    SYSCTLS
    BUGS
    VERSIONS
    SEE ALSO


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