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 2017-09-15 "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 .B #include <sys/socket.h>
  51 .PP
  52 .BI "int getsockopt(int " sockfd ", int " level ", int " optname ,
  53 .BI "               void *" optval ", socklen_t *" optlen );
  54 .BI "int setsockopt(int " sockfd ", 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 options for the socket referred to by the file descriptor
  62 .IR sockfd .
  63 Options may exist at multiple
  64 protocol levels; they are always present at the uppermost
  65 socket level.
  66 .PP
  67 When manipulating socket options, the level at which the
  68 option resides and the name of the option must be specified.
  69 To manipulate options at the sockets API level,
  70 .I level
  71 is specified as
  72 .BR SOL_SOCKET .
  73 To manipulate options at any
  74 other level the protocol number of the appropriate protocol
  75 controlling the option is supplied.
  76 For example,
  77 to indicate that an option is to be interpreted by the
  78 .B TCP
  79 protocol,
  80 .I level
  81 should be set to the protocol number of
  82 .BR TCP ;
  83 see
  84 .BR getprotoent (3).
  85 .PP
  86 The arguments
  87 .I optval
  88 and
  89 .I optlen
  90 are used to access option values for
  91 .BR setsockopt ().
  92 For
  93 .BR getsockopt ()
  94 they identify a buffer in which the value for the
  95 requested option(s) are to be returned.
  96 For
  97 .BR getsockopt (),
  98 .I optlen
  99 is a value-result argument, initially containing the
 100 size of the buffer pointed to by
 101 .IR optval ,
 102 and modified on return to indicate the actual size of
 103 the value returned.
 104 If no option value is to be supplied or returned,
 105 .I optval
 106 may be NULL.
 107 .PP
 108 .I Optname
 109 and any specified options are passed uninterpreted to the appropriate
 110 protocol module for interpretation.
 111 The include file
 112 .I <sys/socket.h>
 113 contains definitions for socket level options, described below.
 114 Options at
 115 other protocol levels vary in format and name; consult the appropriate
 116 entries in section 4 of the manual.
 117 .PP
 118 Most socket-level options utilize an
 119 .I int
 120 argument for
 121 .IR optval .
 122 For
 123 .BR setsockopt (),
 124 the argument should be nonzero to enable a boolean option, or zero if the
 125 option is to be disabled.
 126 .PP
 127 For a description of the available socket options see
 128 .BR socket (7)
 129 and the appropriate protocol man pages.
 130 .SH RETURN VALUE
 131 On success, zero is returned for the standard options.
 132 On error, \-1 is returned, and
 133 .I errno
 134 is set appropriately.
 135 .PP
 136 Netfilter allows the programmer
 137 to define custom socket options with associated handlers; for such
 138 options, the return value on success is the value returned by the handler.
 139 .SH ERRORS
 140 .TP 10
 141 .B EBADF
 142 The argument
 143 .I sockfd
 144 is not a valid file descriptor.
 145 .TP
 146 .B EFAULT
 147 The address pointed to by
 148 .I optval
 149 is not in a valid part of the process address space.
 150 For
 151 .BR getsockopt (),
 152 this error may also be returned if
 153 .I optlen
 154 is not in a valid part of the process address space.
 155 .TP
 156 .B EINVAL
 157 .I optlen
 158 invalid in
 159 .BR setsockopt ().
 160 In some cases this error can also occur for an invalid value in
 161 .IR optval
 162 (e.g., for the
 163 .B IP_ADD_MEMBERSHIP
 164 option described in
 165 .BR ip (7)).
 166 .TP
 167 .B ENOPROTOOPT
 168 The option is unknown at the level indicated.
 169 .TP
 170 .B ENOTSOCK
 171 The file descriptor
 172 .I sockfd
 173 does not refer to a socket.
 174 .SH CONFORMING TO
 175 POSIX.1-2001, POSIX.1-2008,
 176 SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).
 177 .\" SVr4 documents additional ENOMEM and ENOSR error codes, but does
 178 .\" not document the
 179 .\" .BR SO_SNDLOWAT ", " SO_RCVLOWAT ", " SO_SNDTIMEO ", " SO_RCVTIMEO
 180 .\" options
 181 .SH NOTES
 182 POSIX.1 does not require the inclusion of
 183 .IR <sys/types.h> ,
 184 and this header file is not required on Linux.
 185 However, some historical (BSD) implementations required this header
 186 file, and portable applications are probably wise to include it.
 187 .PP
 188 For background on the
 189 .I socklen_t
 190 type, see
 191 .BR accept (2).
 192 .SH BUGS
 193 Several of the socket options should be handled at lower levels of the
 194 system.
 195 .SH SEE ALSO
 196 .BR ioctl (2),
 197 .BR socket (2),
 198 .BR getprotoent (3),
 199 .BR protocols (5),
 200 .BR ip (7),
 201 .BR packet (7),
 202 .BR socket (7),
 203 .BR tcp (7),
 204 .BR udp (7),
 205 .BR unix (7)