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RedHat 9 (Linux i386) - man page for getsockopt (redhat section 2)

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

NAME
       getsockopt, setsockopt - get and set options on sockets

SYNOPSIS
       #include <sys/types.h>
       #include <sys/socket.h>

       int getsockopt(int s, int level, int optname, void *optval, socklen_t *optlen);

       int setsockopt(int s, int level, int optname, const void *optval, socklen_t optlen);

DESCRIPTION
       Getsockopt  and	setsockopt  manipulate the options associated with a socket.  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 socket level, level is specified
       as SOL_SOCKET.  To manipulate options at any other level the protocol number of the appro-
       priate  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  num-
       ber of TCP; see getprotoent(3).

       The  parameters	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 parameter, 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 parameter for optval.  For setsockopt, the param-
       eter should be non-zero to enable a boolean option, or zero if the option is  to  be  dis-
       abled.

       For a description of the available socket options see socket(7) and the appropriate proto-
       col man pages.

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EBADF  The argument s is not a valid descriptor.

       ENOTSOCK
	      The argument s is a file, not a socket.

       ENOPROTOOPT
	      The option is unknown at the level indicated.

       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.

CONFORMING TO
       SVr4, 4.4BSD (these system calls first appeared in  4.2BSD).   SVr4  documents  additional
       ENOMEM  and ENOSR error codes, but does not document the SO_SNDLOWAT, SO_RCVLOWAT, SO_SND-
       TIMEO, SO_RCVTIMEO options

NOTE
       The fifth argument of getsockopt and setsockopt is in reality an int [*] (and this is what
       BSD  4.*  and  libc4  and  libc5  have).   Some	POSIX  confusion  resulted in the present
       socklen_t.  The draft standard has not been adopted yet, but glibc2 already follows it and
       also has socklen_t [*]. 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), unix(7), tcp(7)

Linux Man Page				    1999-05-24				    GETSOCKOPT(2)


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