[chrony-users] Regarding socket permissions

Hi,

Hopefully this isn't appropriate for this channel, I have had a hard time finding an answer externally.

I have a C++ application which would like to send timing information to `chrony`, the goal is sync between an MCU and a linux machine. I think I need to input this as a REFCLOCK.

I see in the chrony code (I'm using v3.5 on ubuntu 20) that after creating the socket it attempts to set the permissions to 666 (R/WR for all) while the owner is root. My problem is that trying to access this socket from the C++ script continuously returns error (13) permission denied.

Current the chrony config is

refclock SOCK /var/run/chrony.ttyACM0.sock

Very basic just to start with. I thought perhaps I could change this to a less restricted location, like

refclock SOCK /tmp/chrony.ttyACM0.sock

Which then results in

chronyd[3550180]: Fatal error : bind(/tmp/chrony.ttyACM0.sock) failed : Permission denied

The connection function is

// acquire a connection to an existing Unix-domain socket
socket_t netlib_localsocket(const char * sockfile, int socktype)
{
  int sock;

  if ((sock = socket(AF_UNIX, socktype, 0)) < 0) {
    return -1;
  } else {
    struct sockaddr_un saddr;

    memset(&saddr, 0, sizeof(struct sockaddr_un));
    saddr.sun_family = AF_UNIX;
    (void)strlcpy(saddr.sun_path, sockfile, sizeof(saddr.sun_path));

    if (connect(sock, (struct sockaddr *)&saddr, SUN_LEN(&saddr)) < 0) {
      (void)close(sock);
      return -2;
    }

    return sock;
  }
}

My C++ application is based off of GPSD, which I can't use directly because I'm not strictly using GPS or NMEA messages and I can't give 100% control of the serial port to any external program. The same application works with SHM, I was attempting with sockets instead as I understand there should be some advantages regarding latency with polling vs interrupt based communications.

Curious if any of you had an idea of what could be wrong..

Best regards,

Morten