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On a listening socket I set the EPOLLIN bit however on client connections I set EPOLLIN | EPOLLOUT bits to struct epoll_event like so: struct epoll_event ev; ev.data.fd = fd; ev.events = EPOLLIN | EPOLLOUT; if (epoll_ctl(evs->epoll_fd, EPOLL_CTL_ADD, fd, &ev) < 0) ... And this is how I test bits: if ((events & EPOLLIN) == EPOLLIN) ... if ((events & EPOLLOUT) == EPOLLOUT) ... I've also tried like: if (events & EPOLLIN) ... if (events & EPOLLOUT) ... Both ways are ALWAYS true! However, whenever I call epoll_wait on my epoll fd, the active file descriptor returned ALWAYS has both bits set even though send() didn't return EAGAIN but when I try to recv() it returns EAGAIN. I have no idea what am I supposed to do when recv() returns EAGAIN, am I supposed to remove the EPOLLOUT flag or what? More code as requested by @Nikolai N Fetissov: static int get_active_fd(events *evs, int index, sstate_t *flags) { uint32_t events = evs->events[index].events; int fd = evs->events[index].data.fd;; if ((events & EPOLLERR) == EPOLLERR || (events & EPOLLHUP) == EPOLLHUP) { close(fd); return -1; } if (events & EPOLLIN) *flags |= DATA_IN; return fd; } void sockset_add(events *evs, int fd) { struct epoll_event ev; ... ev.data.fd = fd; ev.events = EPOLLIN; if (epoll_ctl(evs->epoll_fd, EPOLL_CTL_ADD, fd, &ev) < 0) eprintf("sockset_add(): epoll_ctl(%d) returned an error %d(%s)\n", fd, errno, strerror(errno)); } Then later where I call epoll_wait(): if (flags & DATA_IN) { /* try to read which is impossible because this is never set. */

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