kovidgoyal/kitty · warning

Failed to write to %s wakeup fd with error: %s

Error message

Failed to write to %s wakeup fd with error: %s

What it means

Writing a wakeup byte to the loop's wakeup pipe/eventfd failed; this fd is how other threads and signal handlers rouse the select/epoll io loop, so a lost wakeup may delay processing until the next timeout. Suppressed when called from a signal handler.

Source

Thrown at kitty/loop-utils.c:132

    safe_close(ld->wakeup_read_fd, __FILE__, __LINE__);
#endif
    ld->wakeup_read_fd = -1;
    remove_signal_handlers(ld);
}


void
wakeup_loop(LoopData *ld, bool in_signal_handler, const char *loop_name) {
    while (true) {
#ifdef HAS_EVENT_FD
        static const int64_t value = 1;
        ssize_t ret = write(ld->wakeup_read_fd, &value, sizeof value);
#else
        ssize_t ret = write(ld->wakeup_fds[1], "w", 1);
#endif
        if (ret < 0) {
            if (errno == EINTR) continue;
            if (!in_signal_handler) log_error("Failed to write to %s wakeup fd with error: %s", loop_name, strerror(errno));
        }
        break;
    }
}


void
read_signals(int fd, handle_signal_func callback, void *data) {
#ifdef HAS_SIGNAL_FD
    static struct signalfd_siginfo fdsi[32];
    siginfo_t si;
    while (true) {
        ssize_t s = read(fd, &fdsi, sizeof(fdsi));
        if (s < 0) {
            if (errno == EINTR) continue;
            if (errno == EAGAIN) break;
            log_error("Call to read() from read_signals() failed with error: %s", strerror(errno));
            break;

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Ignore if it appears only during shutdown - benign
2. Upgrade kitty; wakeup race handling improves over time
3. Check for fd leaks (EMFILE) by comparing with ulimit -n
4. Report upstream with a reproducer if it recurs during normal use

When it happens

Trigger: wakeup_io_loop / wakeup_talk_loop / wakeup_write_loop writing to the wakeup fd when it is closed (EBADF), full (EAGAIN on a non-blocking pipe), or under fd exhaustion (EMFILE).

Common situations: Shutdown races where the io loop closes while another thread signals it; fd leaks from other software.

Related errors

• Trying to send data when to pipe is nil
• Too few arguments to pipe function
• Call to read() from read_signals() failed with error: %s
• This must be run as kitten ask
• This should be run as kitten broadcast

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/02a2a92c0514f227. Report an issue: GitHub.