You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.

162 lines
3.9 KiB

/* gpsdate - small utility to set system RTC based on gpsd time
* (C) 2013 by sysmocom - s.f.m.c. GmbH, Author: Harald Welte
* All Rights Reserved
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
/* The idea of this program is that you run it once at system boot time,
* to set the local RTC to the time received by GPS. Further synchronization
* during system runtime is then handled by ntpd, interfacing with gpsd using
* the ntp shared memory protocol.
* However, ntpd is unable to accept a GPS time that's off by more than four
* hours from the system RTC, so initial synchronization has to be done
* externally. 'ntpdate' is the usual option, but doesn't work if you're
* offline. Thus, this gpsdate utilith was created to fill the gap.
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <syslog.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <gps.h>
#define NUM_RETRIES 60 /* Number of gpsd re-connects */
#define RETRY_SLEEP 1 /* Seconds to sleep between re-connects */
static struct gps_data_t gpsdata;
static void callback(struct gps_data_t *gpsdata)
struct timeval tv;
time_t time;
int rc;
if (!(gpsdata->set & TIME_SET))
tv.tv_sec = gpsdata->fix.time;
/* FIXME: use the fractional part for microseconds */
tv.tv_usec = 0;
time = tv.tv_sec;
rc = settimeofday(&tv, NULL);
if (rc == 0) {
syslog(LOG_NOTICE, "Successfully set RTC time to GPSD time:"
" %s", ctime(&time));
} else {
syslog(LOG_ERR, "Error setting RTC: %d (%s)\n",
errno, strerror(errno));
static int osmo_daemonize(void)
int rc;
pid_t pid, sid;
/* Check if parent PID == init, in which case we are already a daemon */
if (getppid() == 1)
return -EEXIST;
/* Fork from the parent process */
pid = fork();
if (pid < 0) {
/* some error happened */
return pid;
if (pid > 0) {
/* if we have received a positive PID, then we are the parent
* and can exit */
/* FIXME: do we really want this? */
/* Create a new session and set process group ID */
sid = setsid();
if (sid < 0)
return sid;
/* Change to the /tmp directory, which prevents the CWD from being locked
* and unable to remove it */
rc = chdir("/tmp");
if (rc < 0)
return rc;
/* Redirect stdio to /dev/null */
/* since C89/C99 says stderr is a macro, we can safely do this! */
#ifdef stderr
freopen("/dev/null", "r", stdin);
freopen("/dev/null", "w", stdout);
freopen("/dev/null", "w", stderr);
return 0;
int main(int argc, char **argv)
char *host = "localhost";
int i, rc;
openlog("gpsdate", LOG_PERROR, LOG_CRON);
if (argc > 1)
host = argv[1];
for (i = 1; i <= NUM_RETRIES; i++) {
printf("Attempt #%d to connect to gpsd at %s...\n", i, host);
rc = gps_open(host, DEFAULT_GPSD_PORT, &gpsdata);
if (!rc)
if (rc) {
syslog(LOG_ERR, "no gpsd running or network error: %d, %s\n",
errno, gps_errstr(errno));
gps_stream(&gpsdata, WATCH_ENABLE|WATCH_JSON, NULL);
gps_mainloop(&gpsdata, 5000000, callback);