adjtimex.c

// 2020, Georg Sauthoff <mail@gms.tf>
//
// Display some clock related system settings.
//
// SPDX-License-Identifier: GPL-3.0-or-later

#include <stdio.h>

#include <sys/timex.h>

int main()
{
    struct timex t = {0};

    int r = adjtimex(&t);
    if (r == -1) {
        perror("adjtimex");
        return 1;
    }

    // this flag is removed by NTP/daemons such as chrony/ptp4l
    // exception: the Solarflare PTPd doesn't remove this flag
    // with STA_UNSYNC unset the kernel writes to the RTC every 11 minutes
    printf("Clock is %ssynchronized (%s)\n", t.status & STA_UNSYNC ? "un" : "",
            t.status & STA_UNSYNC ? "STA_UNSYNC" : "STA_UNSYNC unset");

    printf("Maxerror: %ld us\n", t.maxerror);

    // the offset the kernel uses for CLOCK_TAI, 
    // i.e. clock_gettime(CLOCK_TAI) == clock_gettime(CLOCK_REALTIME) + tai_off
    printf("TAI offset: %d s\n", t.tai);

    printf("PPS frequency discipline (STA_PPSFREQ): %s\n",
            t.status  & STA_PPSFREQ ? "enabled" : "disabled");
    printf("PPS time discipline (STA_PPSTIME): %s\n",
            t.status  & STA_PPSTIME ? "enabled" : "disabled");

    return 0;
}