man2/getsockopt.2

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  34 .\"     $Id: getsockopt.2,v 1.1 1999/05/24 14:57:04 freitag Exp $
  35 .\"
  36 .\" Modified Sat Jul 24 16:19:32 1993 by Rik Faith (faith@cs.unc.edu)
  37 .\" Modified Mon Apr 22 02:29:06 1996 by Martin Schulze (joey@infodrom.north.de)
  38 .\" Modified Tue Aug 27 10:52:51 1996 by Andries Brouwer (aeb@cwi.nl)
  39 .\" Modified Thu Jan 23 13:29:34 1997 by Andries Brouwer (aeb@cwi.nl)
  40 .\" Modified Sun Mar 28 21:26:46 1999 by Andries Brouwer (aeb@cwi.nl)
  41 .\" Modified 1999 by Andi Kleen <ak@muc.de>.
  42 .\"     Removed most stuff because it is in socket.7 now.
  43 .\"
  44 .TH GETSOCKOPT 2 2016-12-12 "Linux" "Linux Programmer's Manual"
  45 .SH NAME
  46 getsockopt, setsockopt \- get and set options on sockets
  47 .SH SYNOPSIS
  48 .nf
  49 .BR "#include <sys/types.h>" "          /* See NOTES */"
  50 .br
  51 .B #include <sys/socket.h>
  52 .sp
  53 .BI "int getsockopt(int " sockfd ", int " level ", int " optname ,
  54 .BI "               void *" optval ", socklen_t *" optlen );
  55 .BI "int setsockopt(int " sockfd ", int " level ", int " optname ,
  56 .BI "               const void *" optval ", socklen_t " optlen );
  57 .fi
  58 .SH DESCRIPTION
  59 .BR getsockopt ()
  60 and
  61 .BR setsockopt ()
  62 manipulate options for the socket referred to by the file descriptor
  63 .IR sockfd .
  64 Options may exist at multiple
  65 protocol levels; they are always present at the uppermost
  66 socket level.
  67
  68 When manipulating socket options, the level at which the
  69 option resides and the name of the option must be specified.
  70 To manipulate options at the sockets API level,
  71 .I level
  72 is specified as
  73 .BR SOL_SOCKET .
  74 To manipulate options at any
  75 other level the protocol number of the appropriate protocol
  76 controlling the option is supplied.
  77 For example,
  78 to indicate that an option is to be interpreted by the
  79 .B TCP
  80 protocol,
  81 .I level
  82 should be set to the protocol number of
  83 .BR TCP ;
  84 see
  85 .BR getprotoent (3).
  86
  87 The arguments
  88 .I optval
  89 and
  90 .I optlen
  91 are used to access option values for
  92 .BR setsockopt ().
  93 For
  94 .BR getsockopt ()
  95 they identify a buffer in which the value for the
  96 requested option(s) are to be returned.
  97 For
  98 .BR getsockopt (),
  99 .I optlen
 100 is a value-result argument, initially containing the
 101 size of the buffer pointed to by
 102 .IR optval ,
 103 and modified on return to indicate the actual size of
 104 the value returned.
 105 If no option value is to be supplied or returned,
 106 .I optval
 107 may be NULL.
 108
 109 .I Optname
 110 and any specified options are passed uninterpreted to the appropriate
 111 protocol module for interpretation.
 112 The include file
 113 .I <sys/socket.h>
 114 contains definitions for socket level options, described below.
 115 Options at
 116 other protocol levels vary in format and name; consult the appropriate
 117 entries in section 4 of the manual.
 118
 119 Most socket-level options utilize an
 120 .I int
 121 argument for
 122 .IR optval .
 123 For
 124 .BR setsockopt (),
 125 the argument should be nonzero to enable a boolean option, or zero if the
 126 option is to be disabled.
 127 .PP
 128 For a description of the available socket options see
 129 .BR socket (7)
 130 and the appropriate protocol man pages.
 131 .SH RETURN VALUE
 132 On success, zero is returned for the standard options.
 133 On error, \-1 is returned, and
 134 .I errno
 135 is set appropriately.
 136
 137 Netfilter allows the programmer
 138 to define custom socket options with associated handlers; for such
 139 options, the return value on success is the value returned by the handler.
 140 .SH ERRORS
 141 .TP 10
 142 .B EBADF
 143 The argument
 144 .I sockfd
 145 is not a valid file descriptor.
 146 .TP
 147 .B EFAULT
 148 The address pointed to by
 149 .I optval
 150 is not in a valid part of the process address space.
 151 For
 152 .BR getsockopt (),
 153 this error may also be returned if
 154 .I optlen
 155 is not in a valid part of the process address space.
 156 .TP
 157 .B EINVAL
 158 .I optlen
 159 invalid in
 160 .BR setsockopt ().
 161 In some cases this error can also occur for an invalid value in
 162 .IR optval
 163 (e.g., for the
 164 .B IP_ADD_MEMBERSHIP
 165 option described in
 166 .BR ip (7)).
 167 .TP
 168 .B ENOPROTOOPT
 169 The option is unknown at the level indicated.
 170 .TP
 171 .B ENOTSOCK
 172 The file descriptor
 173 .I sockfd
 174 does not refer to a socket.
 175 .SH CONFORMING TO
 176 POSIX.1-2001, POSIX.1-2008,
 177 SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).
 178 .\" SVr4 documents additional ENOMEM and ENOSR error codes, but does
 179 .\" not document the
 180 .\" .BR SO_SNDLOWAT ", " SO_RCVLOWAT ", " SO_SNDTIMEO ", " SO_RCVTIMEO
 181 .\" options
 182 .SH NOTES
 183 POSIX.1 does not require the inclusion of
 184 .IR <sys/types.h> ,
 185 and this header file is not required on Linux.
 186 However, some historical (BSD) implementations required this header
 187 file, and portable applications are probably wise to include it.
 188
 189 For background on the
 190 .I socklen_t
 191 type, see
 192 .BR accept (2).
 193 .SH BUGS
 194 Several of the socket options should be handled at lower levels of the
 195 system.
 196 .SH SEE ALSO
 197 .BR ioctl (2),
 198 .BR socket (2),
 199 .BR getprotoent (3),
 200 .BR protocols (5),
 201 .BR ip (7),
 202 .BR packet (7),
 203 .BR socket (7),
 204 .BR tcp (7),
 205 .BR udp (7),
 206 .BR unix (7)