getsockopt(2) System Calls Manual getsockopt(2) getsockopt, setsockopt - (libc -lc) #include int getsockopt(socklen_t *restrict optlen; int sockfd, int level, int optname, void optval[_Nullable restrict *optlen], socklen_t *restrict optlen); int setsockopt(socklen_t optlen; int sockfd, int level, int optname, const void optval[optlen], socklen_t optlen); getsockopt() setsockopt() sockfd. . . 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.1-2024. 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) 3 . . : . 6.18 29 2025 getsockopt(2)