mike@whutt.UUCP (BALDWIN) (07/12/88)
Posting-number: Volume 3, Issue 79
Submitted-by: "BALDWIN" <mike@whutt.UUCP>
Archive-name: utc
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 1-201-653-0351 | 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<---
echo x - utc.c
sed 's/^X//' << \EOF > utc.c
X/*
X * The Naval Observatory clock (+1 202 653 0351) prints this every second:
X *
X * *
X * jjjjj ddd hhmmss UTC
X *
X * jjjjj Julian date modulo 2400000
X * ddd days since beginning of year
X * hhmmss time of day in Universal Time Coordinated
X */
X
X#include <stdio.h>
X#include <time.h>
X#include <sys/types.h>
X
X#define EPOCH 40587 /* UNIX starts JD 2440587, */
X#define leap(y, m) ((y+m-1 - 70%m) / m) /* also known as 1/1/70 */
X#define TONE '*'
X#define TIME "\n%05ld %03d %02d%02d%02d UTC"
X
Xmain(argc, argv)
Xint argc;
Xchar *argv[];
X{
X int setflg = 0, prtflg = 0;
X int y, d, h, m, s;
X long j;
X time_t now;
X int c;
X
X while ((c = getopt(argc, argv, "sp")) != EOF)
X switch (c) {
X case 's': setflg++; break;
X case 'p': prtflg++; break;
X default:
X fprintf(stderr, "usage: %s [-s] [-p]\n", argv[0]);
X return 1;
X }
X if (setflg || prtflg) {
X while ((c = getchar()) != TONE)
X if (c == EOF)
X return 1;
X if (scanf(TIME, &j, &d, &h, &m, &s) != 5)
X return 1;
X now = (((j - EPOCH) * 24 + h) * 60 + m) * 60 + s;
X if (setflg && stime(&now) == -1)
X perror(argv[0]);
X if (prtflg)
X fputs(ctime(&now), stdout);
X } else {
X for (c = 0; c < 60; c++) {
X time(&now);
X s = (now % 60);
X m = (now /= 60) % 60;
X h = (now /= 60) % 24;
X d = (now /= 24) % 365;
X j = now + EPOCH;
X y = (now /= 365);
X d += 1 - leap(y, 4) + leap(y, 100) - leap(y, 400);
X putchar(TONE);
X printf(TIME, j, d, h, m, s);
X putchar('\n');
X fflush(stdout);
X sleep(1);
X }
X }
X return 0;
X}
EOF
exit 0
--
Michael Scott Baldwin research!mike attmail!mike mike@att.arpa
AT&T Bell Laboratories +1 201 386 3052