• NAME
  
  getsockopt, setsockopt - get and set options on sockets
• SYNOPSIS
  

  
   "#include <sys/types.h>" "          /* See NOTES */"
  
   #include <sys/socket.h>
  
   int getsockopt(int  sockfd , int  level , int  optname ,
                   void * optval , socklen_t * optlen );   int setsockopt(int  sockfd , int  level , int  optname ,                  const void * optval , socklen_t  optlen ); 

• DESCRIPTION
  
  getsockopt ()
  and
  setsockopt ()
  manipulate options for the socket referred to by the file descriptor
  sockfd .
  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 sockets API level,
  level
  is specified as
  SOL_SOCKET .
  To manipulate options at any
  other level the protocol number of the appropriate protocol
  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 arguments
  optval
  and
  optlen
  are used to access option values for
  setsockopt ().
  For
  getsockopt ()
  they identify a buffer in which the value for the
  requested option(s) are to be returned.
  For
  getsockopt (),
  optlen
  is a value-result argument, initially containing the
  size of the buffer pointed to by
  optval ,
  and modified on return to indicate the actual size of
  the value returned.
  If no option value is to be supplied or returned,
  optval
  may be NULL.
  
  Optname
  and any specified options are passed uninterpreted to the appropriate
  protocol module for interpretation.
  The include file
  <sys/socket.h>
  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
  argument for
  optval .
  For
  setsockopt (),
  the argument should be non-zero to enable a boolean option, or zero if the
  option is to be disabled.
  
  
  
  For a description of the available socket options see
  socket(7)
  and the appropriate protocol man pages.
  
• RETURN VALUE
  
  On success, zero is returned.
  On error, -1 is returned, and
  errno
  is set appropriately.
  
• ERRORS
  

  EBADF

  The argument
  sockfd
  is not a valid descriptor.
  

  EFAULT

  The address pointed to by
  optval
  is not in a valid part of the process address space.
  For
  getsockopt (),
  this error may also be returned if
  optlen
  is not in a valid part of the process address space.
  

  EINVAL

  optlen
  invalid in
  setsockopt ().
  In some cases this error can also occur for an invalid value in
  optval
  (e.g., for the
  IP_ADD_MEMBERSHIP option described in
  ip(7) ).
  

  ENOPROTOOPT

  The option is unknown at the level indicated.
  

  ENOTSOCK

  The argument
  sockfd
  is a file, not a socket.
  

• CONFORMING TO
  
  SVr4, 4.4BSD (these system calls first appeared in 4.2BSD),
  POSIX.1-2001.
  
  
  
  
  
• NOTES
  
  POSIX.1-2001 does not require the inclusion of
  <sys/types.h> ,
  and this header file is not required on Linux.
  However, some historical (BSD) implementations required this header
  file, and portable applications are probably wise to include it.
  
  The
  optlen
  argument of
  getsockopt ()
  and
  setsockopt ()
  is in reality an
  "int [*]"
  (and this is what 4.x BSD and libc4 and libc5 have).
  Some POSIX confusion resulted in the present
  socklen_t ,
  also used by glibc.
  See also
  accept(2) .
  
• BUGS
  
  Several of the socket options should be handled at lower levels of the
  system.
  
• SEE ALSO
  
  ioctl(2) ,
  socket(2) ,
  getprotoent(3) ,
  protocols(5) ,
  socket(7) ,
  tcp(7) ,
  unix(7)
  
• COLOPHON
  
  This page is part of release 3.19 of the Linux
  man-pages
  project.
  A description of the project,
  and information about reporting bugs,
  can be found at
  http://www.kernel.org/doc/man-pages/.
  

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