getsockopt(2) System Calls Manual getsockopt(2) getsockopt, setsockopt - C (libc, -lc) #include int getsockopt(int sockfd, int level, int optname, void optval[restrict *.optlen], socklen_t *restrict optlen); int setsockopt(int sockfd, int level, int optname, const void optval[.optlen], socklen_t optlen); getsockopt() setsockopt() , sockfd. ; . , . API level SOL_SOCKET. , , . , , TCP, level TCP; getprotoent(3). optval optlen setsockopt() . getsockopt() , . getsockopt() optlen , optval, . , optval NULL. optname . ; . . 4 . int optval. setsockopt() , , . socket(7) . . -1, errno . Netfilter ; , . EBADF sockfd . EFAULT , optval, . getsockopt() , optlen . EINVAL optlen setsockopt(). - optval (, IP_ADD_MEMBERSHIP, ip(7)). ENOPROTOOPT . ENOTSOCK sockfd . POSIX.1-2008. POSIX.1-2001, SVr4, 4.4BSD ( 4.2BSD). . ioctl(2), socket(2), getprotoent(3), protocols(5), ip(7), packet(7), socket(7), tcp(7), udp(7), unix(7) () Azamat Hackimov , Dmitry Bolkhovskikh , Vladislav , Yuri Kozlov , Kirill Rekhov ; GNU (GNU General Public License - GPL, 3 ) , - . - , , () () () <>. Linux 6.9.1 2 2024 . getsockopt(2)