GETSOCKOPT(2)

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

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 con‐
       trolling 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 pro‐
       tocol 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) imple‐
       mentations 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 con‐
       fusion 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 3.23 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/.

Linux                                                                   2008-12-03