Manpage of GETSOCKOPT
GETSOCKOPTSection: Linux Programmer's Manual (2)
NAMEgetsockopt, 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);
DESCRIPTIONgetsockopt() 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, levelis 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 TCPprotocol, levelshould be set to the protocol number of TCP; see getprotoent(3).
The arguments optvaland optlenare 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(), optlenis 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, optvalmay be NULL.
Optnameand 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 intargument for optval. For setsockopt(), 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.
RETURN VALUEOn success, zero is returned for the standard options. On error, -1 is returned, and errnois set appropriately.
- The argument sockfdis not a valid file descriptor.
- The address pointed to by optvalis not in a valid part of the process address space. For getsockopt(), this error may also be returned if optlenis not in a valid part of the process address space.
- optleninvalid in setsockopt(). In some cases this error can also occur for an invalid value in optval(e.g., for the IP_ADD_MEMBERSHIPoption described in ip(7)).
- The option is unknown at the level indicated.
- The file descriptor sockfddoes not refer to a socket.
CONFORMING TOPOSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).
NOTESPOSIX.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_ttype, see accept(2).
BUGSSeveral of the socket options should be handled at lower levels of the system.
SEE ALSOioctl(2), socket(2), getprotoent(3), protocols(5), ip(7), packet(7), socket(7), tcp(7), udp(7), unix(7)
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