GETSOCKOPT(2) BSD System Calls Manual GETSOCKOPT(2)

NAME
     ggeettssoocckkoopptt, sseettssoocckkoopptt - get and set options on sockets

SYNOPSIS
     ##iinncclluuddee <>

     int
     ggeettssoocckkoopptt(int socket, int level, int optionname,
         void *restrict optionvalue, socklent *restrict optionlen);

     int
     sseettssoocckkoopptt(int socket, int level, int optionname,
         const void *optionvalue, socklent optionlen);

DESCRIPTION
     GGeettssoocckkoopptt() and sseettssoocckkoopptt() manipulate the options associated with a
     socket.  Options may exist at multiple protocol levels; they are always
     present at the uppermost ``socket'' level.

     When manipulating socket options the level at which the option resides
     and the name of the option must be specified.  To manipulate options at
     the socket level, level is specified as SOLSOCKET.  To manipulate
     options at any other level the protocol number of the appropriate proto-
     col controlling the option is supplied.  For example, to indicate that an
     option is to be interpreted by the TCP protocol, level should be set to
     the protocol number of TCP; see getprotoent(3).

     The parameters optionvalue and optionlen are used to access option val-
     ues for sseettssoocckkoopptt().  For ggeettssoocckkoopptt() they identify a buffer in which
     the value for the requested option(s) are to be returned.  For
     ggeettssoocckkoopptt(), optionlen is a value-result parameter, initially contain-
     ing the size of the buffer pointed to by optionvalue, and modified on
     return to indicate the actual size of the value returned.  If no option
     value is to be supplied or returned, optionvalue may be NULL.

     optionname and any specified options are passed uninterpreted to the
     appropriate protocol module for interpretation.  The include file
      contains definitions for socket level options, described
     below.  Options at other protocol levels vary in format and name; consult
     the appropriate entries in section 4 of the manual.

     Most socket-level options utilize an int parameter for optionvalue.  For
     sseettssoocckkoopptt(), the parameter should be non-zero to enable a boolean
     option, or zero if the option is to be disabled.  SOLINGER uses a struct
     linger parameter, defined in , which specifies the desired
     state of the option and the linger interval (see below).  SOSNDTIMEO and
     SORCVTIMEO use a struct timeval parameter, defined in .

     The following options are recognized at the socket level.  Except as
     noted, each may be examined with ggeettssoocckkoopptt() and set with sseettssoocckkoopptt().

           SODEBUG        enables recording of debugging information
           SOREUSEADDR    enables local address reuse
           SOREUSEPORT    enables duplicate address and port bindings
           SOKEEPALIVE    enables keep connections alive
           SODONTROUTE    enables routing bypass for outgoing messages
           SOLINGER       linger on close if data present
           SOBROADCAST    enables permission to transmit broadcast messages
           SOOOBINLINE    enables reception of out-of-band data in band
           SOSNDBUF       set buffer size for output
           SORCVBUF       set buffer size for input
           SOSNDLOWAT     set minimum count for output
           SORCVLOWAT     set minimum count for input
           SOSNDTIMEO     set timeout value for output
           SORCVTIMEO     set timeout value for input
           SOTYPE         get the type of the socket (get only)
           SOERROR        get and clear error on the socket (get only)
           SONOSIGPIPE    do not generate SIGPIPE, instead return EPIPE

     SODEBUG enables debugging in the underlying protocol modules.
     SOREUSEADDR indicates that the rules used in validating addresses sup-
     plied in a bind(2) call should allow reuse of local addresses.
     SOREUSEPORT allows completely duplicate bindings by multiple processes
     if they all set SOREUSEPORT before binding the port.  This option per-
     mits multiple instances of a program to each receive UDP/IP multicast or
     broadcast datagrams destined for the bound port.  SOKEEPALIVE enables
     the periodic transmission of messages on a connected socket.  Should the
     connected party fail to respond to these messages, the connection is con-
     sidered broken and processes using the socket are notified via a SIGPIPE
     signal when attempting to send data.  SODONTROUTE indicates that outgo-
     ing messages should bypass the standard routing facilities.  Instead,
     messages are directed to the appropriate network interface according to
     the network portion of the destination address.

     SOLINGER controls the action taken when unsent messages are queued on
     socket and a close(2) is performed.  If the socket promises reliable
     delivery of data and SOLINGER is set, the system will block the process
     on the close attempt until it is able to transmit the data or until it
     decides it is unable to deliver the information (a timeout period, termed
     the linger interval, is specified in the sseettssoocckkoopptt() call when SOLINGER
     is requested).  If SOLINGER is disabled and a close is issued, the sys-
     tem will process the close in a manner that allows the process to con-
     tinue as quickly as possible.

     The option SOBROADCAST requests permission to send broadcast datagrams
     on the socket.  Broadcast was a privileged operation in earlier versions
     of the system.  With protocols that support out-of-band data, the
     SOOOBINLINE option requests that out-of-band data be placed in the nor-
     mal data input queue as received; it will then be accessible with recv or
     read calls without the MSGOOB flag.  Some protocols always behave as if
     this option is set.  SOSNDBUF and SORCVBUF are options to adjust the
     normal buffer sizes allocated for output and input buffers, respectively.
     The buffer size may be increased for high-volume connections, or may be
     decreased to limit the possible backlog of incoming data.  The system
     places an absolute limit on these values.

     SOSNDLOWAT is an option to set the minimum count for output operations.
     Most output operations process all of the data supplied by the call,
     delivering data to the protocol for transmission and blocking as neces-
     sary for flow control.  Nonblocking output operations will process as
     much data as permitted (subject to flow control) without blocking, but
     will process no data if flow control does not allow the smaller of the
     low-water mark value or the entire request to be processed.  A select(2)
     operation testing the ability to write to a socket will return true only
     if the low-water mark amount could be processed.  The default value for
     SOSNDLOWAT is set to a convenient size for network efficiency, often
     1024.

     SORCVLOWAT is an option to set the minimum count for input operations.
     In general, receive calls will block until any (non-zero) amount of data
     is received, then return with the smaller of the amount available or the
     amount requested.  The default value for SORCVLOWAT is 1.  If
     SORCVLOWAT is set to a larger value, blocking receive calls normally
     wait until they have received the smaller of the low-water mark value or
     the requested amount.  Receive calls may still return less than the low-
     water mark if an error occurs, a signal is caught, or the type of data
     next in the receive queue is different than that returned.

     SOSNDTIMEO is an option to set a timeout value for output operations.
     It accepts a struct timeval parameter with the number of seconds and
     microseconds used to limit waits for output operations to complete.  If a
     send operation has blocked for this much time, it returns with a partial
     count or with the error EWOULDBLOCK if no data were sent.  In the current
     implementation, this timer is restarted each time additional data are
     delivered to the protocol, implying that the limit applies to output por-
     tions ranging in size from the low-water mark to the high-water mark for
     output.

     SORCVTIMEO is an option to set a timeout value for input operations.  It
     accepts a struct timeval parameter with the number of seconds and
     microseconds used to limit waits for input operations to complete.  In
     the current implementation, this timer is restarted each time additional
     data are received by the protocol, and thus the limit is in effect an
     inactivity timer.  If a receive operation has been blocked for this much
     time without receiving additional data, it returns with a short count or
     with the error EWOULDBLOCK if no data were received.  The struct timeval
     parameter must represent a positive time interval; otherwise,
     sseettssoocckkoopptt() returns with the error EDOM.

     SONOSIGPIPE is an option that prevents SIGPIPE from being raised when a
     write fails on a socket to which there is no reader; instead, the write
     to the socket returns with the error EPIPE when there is no reader.

     Finally, SOTYPE and SOERROR are options used only with ggeettssoocckkoopptt().
     SOTYPE returns the type of the socket, such as SOCKSTREAM; it is useful
     for servers that inherit sockets on startup.  SOERROR returns any pend-
     ing error on the socket and clears the error status.  It may be used to
     check for asynchronous errors on connected datagram sockets or for other
     asynchronous errors.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

EERRRROORRSS
     The ggeettssoocckkoopptt() and sseettssoocckkoopptt() system calls will succeed unless:

     [EBADF]            The argument socket is not a valid file descriptor.

     [EFAULT]           The address pointed to by optionvalue is not in a
                        valid part of the process address space.  For
                        ggeettssoocckkoopptt(), this error may also be returned if
                        optionlen is not in a valid part of the process
                        address space.

     [EINVAL]           The option is invalid at the level indicated.

     [ENOBUFS]          Insufficient memory buffers are available.

     [ENOPROTOOPT]      The option is unknown at the level indicated.

     [ENOTSOCK]         The argument socket is not a socket (e.g., a plain
                        file).

     The sseettssoocckkoopptt() system call will succeed unless:

     [EDOM]             The argument optionvalue is out of bounds.

     [EISCONN]          socket is already connected and a specified option
                        cannot be set while this is the case.

LEGACY SYNOPSIS
     ##iinncclluuddee <>
     ##iinncclluuddee <>

     The include file  is necessary.

SEE ALSO
     ioctl(2), socket(2), getprotoent(3), protocols(5)

BUGS
     Several of the socket options should be handled at lower levels of the
     system.

HISTORY     The ggeettssoocckkoopptt() system call appeared in 4.2BSD.

4.3-Reno Berkeley Distribution  April 19, 1994  4.3-Reno Berkeley Distribution