man2/getsockopt.2

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  32 .\"     $Id: getsockopt.2,v 1.1 1999/05/24 14:57:04 freitag Exp $
  33 .\"
  34 .\" Modified Sat Jul 24 16:19:32 1993 by Rik Faith (faith@cs.unc.edu)
  35 .\" Modified Mon Apr 22 02:29:06 1996 by Martin Schulze (joey@infodrom.north.de)
  36 .\" Modified Tue Aug 27 10:52:51 1996 by Andries Brouwer (aeb@cwi.nl)
  37 .\" Modified Thu Jan 23 13:29:34 1997 by Andries Brouwer (aeb@cwi.nl)
  38 .\" Modified Sun Mar 28 21:26:46 1999 by Andries Brouwer (aeb@cwi.nl)
  39 .\" Modified 1999 by Andi Kleen <ak@muc.de>.
  40 .\"     Removed most stuff because it is in socket.7 now.
  41 .\"
  42 .TH GETSOCKOPT 2 1999-05-24 "Linux" "Linux Programmer's Manual"
  43 .SH NAME
  44 getsockopt, setsockopt \- get and set options on sockets
  45 .SH SYNOPSIS
  46 .nf
  47 .BR "#include <sys/types.h>" "          /* See NOTES */"
  48 .br
  49 .B #include <sys/socket.h>
  50 .sp
  51 .BI "int getsockopt(int " s ", int " level ", int " optname ,
  52 .BI "               void *" optval ", socklen_t *" optlen );
  53 .sp
  54 .BI "int setsockopt(int " s ", int " level ", int " optname ,
  55 .BI "               const void *" optval ", socklen_t " optlen );
  56 .fi
  57 .SH DESCRIPTION
  58 .BR getsockopt ()
  59 and
  60 .BR setsockopt ()
  61 manipulate the
  62 .I options
  63 associated with a socket.
  64 Options may exist at multiple
  65 protocol levels; they are always present at the uppermost
  66 .B socket
  67 level.
  68
  69 When manipulating socket options the level at which the
  70 option resides and the name of the option must be specified.
  71 To manipulate options at the socket level,
  72 .I level
  73 is specified as
  74 .BR SOL_SOCKET .
  75 To manipulate options at any
  76 other level the protocol number of the appropriate protocol
  77 controlling the option is supplied.
  78 For example,
  79 to indicate that an option is to be interpreted by the
  80 .B TCP
  81 protocol,
  82 .I level
  83 should be set to the protocol number of
  84 .BR TCP ;
  85 see
  86 .BR getprotoent (3).
  87
  88 The parameters
  89 .I optval
  90 and
  91 .I optlen
  92 are used to access option values for
  93 .BR setsockopt ().
  94 For
  95 .BR getsockopt ()
  96 they identify a buffer in which the value for the
  97 requested option(s) are to be returned.
  98 For
  99 .BR getsockopt (),
 100 .I optlen
 101 is a value-result parameter, initially containing the
 102 size of the buffer pointed to by
 103 .IR optval ,
 104 and modified on return to indicate the actual size of
 105 the value returned.
 106 If no option value is to be supplied or returned,
 107 .I optval
 108 may be NULL.
 109
 110 .I Optname
 111 and any specified options are passed uninterpreted to the appropriate
 112 protocol module for interpretation.
 113 The include file
 114 .I <sys/socket.h>
 115 contains definitions for socket level options, described below.
 116 Options at
 117 other protocol levels vary in format and name; consult the appropriate
 118 entries in section 4 of the manual.
 119
 120 Most socket-level options utilize an
 121 .I int
 122 parameter for
 123 .IR optval .
 124 For
 125 .BR setsockopt (),
 126 the parameter should be non-zero to enable a boolean option, or zero if the
 127 option is to be disabled.
 128 .PP
 129 For a description of the available socket options see
 130 .BR socket (7)
 131 and the appropriate protocol man pages.
 132 .SH "RETURN VALUE"
 133 On success, zero is returned.
 134 On error, \-1 is returned, and
 135 .I errno
 136 is set appropriately.
 137 .SH ERRORS
 138 .TP 10
 139 .B EBADF
 140 The argument
 141 .I s
 142 is not a valid descriptor.
 143 .TP
 144 .B EFAULT
 145 The address pointed to by
 146 .I optval
 147 is not in a valid part of the process address space.
 148 For
 149 .BR getsockopt (),
 150 this error may also be returned if
 151 .I optlen
 152 is not in a valid part of the process address space.
 153 .TP
 154 .B EINVAL
 155 .I optlen
 156 invalid in
 157 .BR setsockopt ().
 158 .TP
 159 .B ENOPROTOOPT
 160 The option is unknown at the level indicated.
 161 .TP
 162 .B ENOTSOCK
 163 The argument
 164 .I s
 165 is a file, not a socket.
 166 .SH "CONFORMING TO"
 167 SVr4, 4.4BSD (these system calls first appeared in 4.2BSD),
 168 POSIX.1-2001.
 169 .\" SVr4 documents additional ENOMEM and ENOSR error codes, but does
 170 .\" not document the
 171 .\" .BR SO_SNDLOWAT ", " SO_RCVLOWAT ", " SO_SNDTIMEO ", " SO_RCVTIMEO
 172 .\" options
 173 .SH NOTES
 174 POSIX.1-2001 does not require the inclusion of
 175 .IR <sys/types.h> ,
 176 and this header file is not required on Linux.
 177 However, some historical (BSD) implementations required this header
 178 file, and portable applications are probably wise to include it.
 179
 180 The
 181 .I optlen
 182 argument of
 183 .BR getsockopt ()
 184 and
 185 .BR setsockopt ()
 186 is in reality an
 187 .I "int [*]"
 188 (and this is what 4.x BSD and libc4 and libc5 have).
 189 Some POSIX confusion resulted in the present
 190 .IR socklen_t ,
 191 also used by glibc.
 192 See also
 193 .BR accept (2).
 194 .SH BUGS
 195 Several of the socket options should be handled at lower levels of the
 196 system.
 197 .SH "SEE ALSO"
 198 .BR ioctl (2),
 199 .BR socket (2),
 200 .BR getprotoent (3),
 201 .BR protocols (5),
 202 .BR socket (7),
 203 .BR tcp (7),
 204 .BR unix (7)