Path: utzoo!utgpu!watserv1!watmath!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!rpi!uupsi!jpradley!jpr
From: jpr@jpradley.jpr.com (Jean-Pierre Radley)
Newsgroups: comp.sources.d
Subject: Re: Obtaining time info from Naval Observatory
Message-ID: <1991Jan10.010808.27118@jpradley.jpr.com>
Date: 10 Jan 91 01:08:08 GMT
References: <1991Jan09.003434.5379@esleng.uucp>
Reply-To: jpr@jpradley.UUCP (Jean-Pierre Radley)
Organization: NYC Public Unix
Lines: 129

In article <1991Jan09.003434.5379@esleng.uucp> dag@esleng.uucp (David A. Gilmour) writes:
>I have seen references to a program which can automatically obtain
>the time from the Naval Observatory and update the system clock.
>
>If anyone knows where I can get the source for this program I'd
>appreciate a note via mail.

It isn't all that long, so here goes:


|From: mike@whutt.UUCP (BALDWIN)
|Newsgroups: sci.astro,comp.dcom.modems,rec.ham-radio
|Subject: Re: N.B.S. Time Service
|Summary: I've got (a small) one
|Keywords: naval observatory
|Message-ID: <3507@whutt.UUCP>
|Date: 12 Jul 88 14:54:40 GMT
|References: <455@trane.UUCP> <303@macomw.ARPA> <56@stanton.TCC.COM> <12277@mimsy.UUCP>
|Distribution: na
|Organization: AT&T Bell Laboratories
|Lines: 108
 	In article <56@stanton.TCC.COM> donegan@stanton.TCC.COM
> 				(Steven P. Donegan) writes:
>
> 	I came across a dos based time service program that used a
> 	Hayes modem to autodial the Naval Observatory in the Wash. DC
> 	area (I think) and retrieved the REAL time (plus/minus a second
> 	or so). If anyone knows of source for a similar program that I
> 	could port to my UNIX system I'd appreciate having it.

I've been running such a program, which I wrote, at home for over six
months now.  It's written in C, and runs under System V (or any UNIX
system with an stime(2) system call).  It consists of a single program
called "utc" (universal time coordinated).  When invoked with options,
it reads the Naval clock and does one or both of these things:

	-s	sets the time via stime(2)
	-p	prints the time via ctime(3C)

If it can't read the time from the standard input, it exits non-zero.
When invoked without options, it prints the time in Naval clock format
for about a minute.  Thus, it can be installed as a login shell to provide
time service for your other systems without having them all call DC.
As a test, "utc | utc -p" should print the current time.  You can pipe
cu right into it, so set up a crontab entry to execute

	cu 1-202-653-0351 | utc -s

You may have to fix your cu to die properly when it receives a SIGPIPE.
I have my crontab entry run once a day, but it only calls DC if the
time hasn't been set in over a week.  A simple shell file accomplishes
this:

	LAST=/etc/.lastutc
	[ -z "`find $LAST -mtime -7 -print`" ] &&
	cu 1-202-653-0351 | utc -s && >$LAST

---8<--------8<---------- cut here for utc.c ------------8<--------------8<---
/*
 * The Naval Observatory clock (+1 202 653 0351) prints this every second:
 *
 *	*
 *	jjjjj ddd hhmmss UTC
 *
 * jjjjj	Julian date modulo 2400000
 * ddd		days since beginning of year
 * hhmmss	time of day in Universal Time Coordinated
 */

#include <stdio.h>
#include <time.h>
#include <sys/types.h>

#define	EPOCH		40587			/* UNIX starts JD 2440587, */
#define	leap(y, m)	((y+m-1 - 70%m) / m)	/* also known as 1/1/70 */
#define	TONE		'*'
#define	TIME		"\n%05ld %03d %02d%02d%02d UTC"

main(argc, argv)
int	argc;
char	*argv[];
{
	int	setflg = 0, prtflg = 0;
	int	y, d, h, m, s;
	long	j;
	time_t	now;
	int	c;

	while ((c = getopt(argc, argv, "sp")) != EOF)
		switch (c) {
		case 's': setflg++; break;
		case 'p': prtflg++; break;
		default:
			fprintf(stderr, "usage: %s [-s] [-p]\n", argv[0]);
			return 1;
		}
	if (setflg || prtflg) {
		while ((c = getchar()) != TONE)
			if (c == EOF)
				return 1;
		if (scanf(TIME, &j, &d, &h, &m, &s) != 5)
			return 1;
		now = (((j - EPOCH) * 24 + h) * 60 + m) * 60 + s;
		if (setflg && stime(&now) == -1)
			perror(argv[0]);
		if (prtflg)
			fputs(ctime(&now), stdout);
	} else {
		for (c = 0; c < 60; c++) {
			time(&now);
			s = (now % 60);
			m = (now /= 60) % 60;
			h = (now /= 60) % 24;
			d = (now /= 24) % 365;
			j = now + EPOCH;
			y = (now /= 365);
			d += 1 - leap(y, 4) + leap(y, 100) - leap(y, 400);
			putchar(TONE);
			printf(TIME, j, d, h, m, s);
			putchar('\n');
			fflush(stdout);
			sleep(1);
		}
	}
	return 0;
}
-- 

 Jean-Pierre Radley	    NYC Public Unix	jpr@jpr.com	CIS: 72160,1341