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