📄 getsockopt.html

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>getsockopt</title></head><body bgcolor=white><center><font size=2>The Single UNIX &reg; Specification, Version 2<br>Copyright &copy; 1997 The Open Group</font></center><hr size=2 noshade><h4>NAME</h4><blockquote>getsockopt - get the socket options</blockquote><h4>SYNOPSIS</h4><blockquote><pre><code>#include &lt;<a href="syssocket.h.html">sys/socket.h</a>&gt;int getsockopt(int <I>socket</I>, int <I>level</I>, int <I>option_name,</I>      void *<I>option_value</I>, socklen_t *<I>option_len</I>);</code></pre></blockquote><h4>DESCRIPTION</h4><blockquote>The<i>getsockopt()</i>function retrieves the value for theoption specified by the <I>option_name</I> argument for thesocket specified by the <I>socket</I> argument.  If the sizeof the option value is greater than <I>option_len</I>, thevalue stored in the object pointed to by the <I>option_value</I>argument will be silently truncated.  Otherwise, the objectpointed to by the <I>option_len</I> argument will be modifiedto indicate the actual length of the value.<p>The <I>level</I> argument specifies the protocol level at whichthe option resides.  To retrieve optionsat the socket level, specify the <I>level</I> argument as SOL_SOCKET.  Toretrieve options at other levels, supply the appropriate protocol number forthe protocol controlling the option.  For example, to indicate that an optionwill be interpreted by the TCP (Transport Control Protocol), set <I>level</I>to the protocol number of TCP, as defined in the &lt;<B>netinet/in.h</B>&gt; header,or as determined by using<i><a href="getprotobyname.html">getprotobyname()</a></i>function.<p>The socket in use may require the process to have appropriateprivileges to use the<i>getsockopt()</i>function.<p>The <I>option_name</I> argument specifies a single option to be retrieved.  Itcan be one of the following values defined in<i><a href="syssocket.h.html">&lt;sys/socket.h&gt;</a></i>:<dl compact><dt>SO_DEBUG<dd>Reports whether debugging information is being recorded.This option stores an <B>int</B> value.This is a boolean option.<dt>SO_ACCEPTCONN<dd>Reports whether socket listening is enabled.  This option stores an <B>int</B>value.<dt>SO_BROADCAST<dd>Reports whether transmission of broadcast messages is supported, if this issupported by the protocol.  This option stores an <B>int</B> value.This is a boolean option.<dt>SO_REUSEADDR<dd>Reports whether the rules used in validating addresses supplied to<i><a href="bind.html">bind()</a></i>should allow reuse of local addresses, if this is supported by the protocol.This option stores an <B>int</B> value.This is a boolean option.<dt>SO_KEEPALIVE<dd>Reports whether connections are kept active with periodic transmission ofmessages, if this is supported by the protocol.If the connected socket fails to respond to these messages, the connection isbroken and processes writing to that socket are notified with a SIGPIPEsignal.  This option stores an <B>int</B> value.This is a boolean option.<dt>SO_LINGER<dd>Reports whether the socket lingers on<i><a href="close.html">close()</a></i>if data is present.  If SO_LINGER is set, the system blocks the process during<i><a href="close.html">close()</a></i>until it can transmit the data or until the end of the interval indicated bythe <B>l_linger</B> member, whichever comes first.  If SO_LINGER is notspecified, and<i><a href="close.html">close()</a></i>is issued, the system handles the call in a way that allows the process tocontinue as quickly as possible.  This option stores a <B>linger</B>structure.<dt>SO_OOBINLINE<dd>Reports whether the socket leaves received out-of-band data (data markedurgent) in line.  This option stores an <B>int</B> value.This is a boolean option.<dt>SO_SNDBUF<dd>Reports send buffer size information.  This option stores an <B>int</B> value.<dt>SO_RCVBUF<dd>Reports receive buffer size information.  This option stores an <B>int</B>value.<dt>SO_ERROR<dd>Reports information about error status and clears it.This option stores an <B>int</B> value.<dt>SO_TYPE<dd>Reports the socket type.  This option stores an <B>int</B> value.<dt>SO_DONTROUTE<dd>Reports whether outgoing messages bypassthe standard routing facilities.The destination must be on a directly-connected network, and messages are directed to the appropriate network interface accordingto the destination address. The effect, if any,of this option depends on what protocol isin use. This option stores an <B>int</B>value.This is a boolean option.<dt>SO_RCVLOWAT<dd>Reports the minimum number of bytes to process for socket input operations.  The default valuefor SO_RCVLOWAT is 1.  If SO_RCVLOWAT is set to a larger value, blocking receive calls normally wait until they have received the smaller of thelow water mark value or the requested amount. (They may 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 isdifferent than that returned, e.g. out of band data). This option stores an <B>int</B>value.Note that not all implementations allow this option to be retrieved.<dt>SO_RCVTIMEO<dd>Reports the timeout value for input operations.This option stores a <B>timeval</B>structure with the number ofseconds and microseconds specifying the limit on how long to wait for an input operationto complete.  If a receive operation has blockedfor this much time without receiving additionaldata, it returns with a partial count orerrno set to [EAGAIN] or [EWOULDBLOCK] if no data were received.  The default for thisoption is zero, which indicates that a receiveoperationwill not time out.Note that not all implementations allow this option to be retrieved.<dt>SO_SNDLOWAT<dd>Reports the minimum number of bytes to process forsocket output operations. Non-blocking outputoperations  will process no data if flow controldoes not allow the smaller of the send lowwater mark value or the entire request to be processed.This option stores an <B>int</B>value.Note that not all implementations allow this option to be retrieved.<dt>SO_SNDTIMEO<dd>Reports the timeout value specifying the amount of time that an output function blocks because flow control prevents data from being sent.If a send operation has blocked for this time, it returns with a partial count orwith errno set to [EAGAIN] or [EWOULDBLOCK] if no data were sent.  The default for this option is zero, which indicates that a send operationwill not time out.The option stores a <B>timeval</B>structure.Note that not all implementations allow this option to be retrieved.</dl><p>For boolean options, a zero value indicates that the option is disabled and a non-zero value indicates that theoption is enabled.<p>Options at other protocol levels vary in format and name.<p>The socket in use may require the process to have appropriateprivileges to use the<i>getsockopt()</i>function.</blockquote><h4>RETURN VALUE</h4><blockquote>Upon successful completion,<i>getsockopt()</i>returns 0.  Otherwise, -1 is returned and<I>errno</I> is set to indicate the error.</blockquote><h4>ERRORS</h4><blockquote>The<i>getsockopt()</i>function will fail if:<dl compact><dt>[EBADF]<dd>The <I>socket</I> argument is not a valid file descriptor.<dt>[EFAULT]<dd>The <I>option_value</I>or <I>option_len</I>parameter can not be accessed or written.<dt>[EINVAL]<dd>The specified option is invalid at the specified socket level.<dt>[ENOPROTOOPT]<dd>The option is not supported by the protocol.<dt>[ENOTSOCK]<dd>The <I>socket</I> argument does not refer to a socket.</dl><p>The<i>getsockopt()</i>function may fail if:<dl compact><dt>[EACCES]<dd>The calling process does not have the appropriate privileges.<dt>[EINVAL]<dd>The socket has been shut down.<dt>[ENOBUFS]<dd>Insufficient resources are available in the system to complete the call.<dt>[ENOSR]<dd>There were insufficient STREAMS resources available for the operation tocomplete.</dl></blockquote><h4>SEE ALSO</h4><blockquote><i><a href="bind.html">bind()</a></i>,<i><a href="close.html">close()</a></i>,<i><a href="endprotoent.html">endprotoent()</a></i>,<i><a href="setsockopt.html">setsockopt()</a></i>,<i><a href="socket.html">socket()</a></i>,<i><a href="syssocket.h.html">&lt;sys/socket.h&gt;</a></i>.</blockquote><hr size=2 noshade><center><font size=2>UNIX &reg; is a registered Trademark of The Open Group.<br>Copyright &copy; 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>
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