Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


GETSOCKOPT(2) Linux Programmer's Manual GETSOCKOPT(2)


     getsockopt, setsockopt - get and set options on sockets


     #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);


     getsockopt()   and  setsockopt()  manipulate  options  for  the  socket
     referred to by the file descriptor sockfd.  Options may exist at multi-
     ple  protocol  levels;  they are always present at the uppermost socket
     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 pro-
     tocol 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  getsock-
     opt(), 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; con-
     sult the appropriate entries in section 4 of the manual.
     Most socket-level options utilize an int argument for optval.  For set-
     sockopt(),  the  argument should be nonzero 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.


     On success, zero is returned for the standard options.  On error, -1 is
     returned, and errno is set appropriately.
     Netfilter allows the programmer to define custom  socket  options  with
     associated  handlers;  for such options, the return value on success is
     the value returned by the handler.


     EBADF     The argument sockfd is not a valid file 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)).
               The option is unknown at the level indicated.
     ENOTSOCK  The file descriptor sockfd does not refer to a socket.


     POSIX.1-2001,  POSIX.1-2008,  SVr4,  4.4BSD  (these  system calls first
     appeared in 4.2BSD).


     POSIX.1 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.
     For background on the socklen_t type, see accept(2).


     Several  of the socket options should be handled at lower levels of the


     ioctl(2), socket(2), getprotoent(3),  protocols(5),  ip(7),  packet(7),
     socket(7), tcp(7), udp(7), unix(7)


     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at

Linux 2017-09-15 GETSOCKOPT(2)

/data/webs/external/dokuwiki/data/pages/man/setsockopt.txt · Last modified: 2019/05/17 09:32 by

Was this page helpful?-10+1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki