Re: Setting computer time from Internet

[Irving_Wolfe]

On Sat, Oct 23, 1999 at 04:22:48PM -0400, Denis Voitenko wrote:
> > > 13 * * * * rdate your.isps.rdate.server >/dev/null 2>&1 && clock -w
> 
> I could not find the rdate command on my Slackware 4. Where can I download
> the package? Freshmeat did not find it for me.

It's tiny, so here it is, as an attachment; I hope
the mailing-list system allows attachments.

Regards,
 - Irving
-
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#ifndef lint
static char sccsid[] = "@(#)rdate.c 1.1 92/07/30";
#endif

/* 
 * Copyright (c) 1983 by Sun Microsystems, Inc.
 */

/*
 *  rdate - get date from remote machine
 *
 *      sets time, obtaining value from host
 *      on the tcp/time socket.  Since timeserver returns
 *      with time of day in seconds since Jan 1, 1900,  must
 *      subtract 86400(365*70 + 17) to get time
 *      since Jan 1, 1970, which is what get/settimeofday
 *      uses.
 */
/* #define      TOFFSET (86400*(365*70 + 17)) */
/*
 * Some compilers complain if cast not included even if expr is
 * being assigned to a long.  Go figure...
 */
#define TOFFSET ((long)86400*(365*70 + 17))

/* original value was in 1983, so set sanity chk to a more recent value */
#define WRITTEN 891417600               /* tv_sec when built */

#include <signal.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>

int timeout();

main(argc, argv)
        int argc;
        char **argv;
{
        struct sockaddr_in server;
        struct sockaddr from;
        int s, i;
        u_long time;
        struct servent *sp;
        struct protoent *pp;
        struct hostent *hp;
        struct timeval timestruct;

        if (argc != 2) {
                fprintf(stderr, "usage: rdate host\n");
                exit(1);
        }
        if ((hp = gethostbyname(argv[1])) == NULL) {
                fprintf(stderr, "Sorry, host %s not in hosts database\n",
                    argv[1]);
                exit(1);
        }
        if ((sp = getservbyname("time", "tcp")) == NULL) {
                fprintf(stderr,
                    "Sorry, time service not in services database\n");
                exit(1);
        }
        if ((pp = getprotobyname("tcp")) == NULL) {
                fprintf(stderr,
                    "Sorry, TCP protocol not in protocols database\n");
                exit(1);
        }
        if ((s = socket(AF_INET, SOCK_STREAM, pp->p_proto)) == 0) {
                perror("rdate: socket");
                exit(1);
        }

        bzero((char *)&server, sizeof (server));
        bcopy(hp->h_addr, (char *)&server.sin_addr, hp->h_length);
        server.sin_family = hp->h_addrtype;
        server.sin_port = sp->s_port;

        if (connect(s, &server, sizeof (server)) < 0) {
                perror("rdate: connect");
                exit(1);
        }

        alarm(10);                      /* perhaps this should be larger? */
        signal(SIGALRM, timeout);

        if (read(s, (char *)&time, sizeof (int)) != sizeof (int)) {
                perror("rdate: read");
                exit(1);
        }
        time = ntohl(time) - TOFFSET;
        /* date must be later than when program was written */
        if (time < WRITTEN) {
                fprintf(stderr, "didn't get plausible time from %s\n",
                    argv[1]);
                exit(1);
        }
        timestruct.tv_usec = 0;
        timestruct.tv_sec = time;
        i = settimeofday(&timestruct, 0);
        if (i == -1)
                perror("couldn't set time of day");
        else
                printf("%s", ctime(&timestruct.tv_sec));
        exit(0);
        /* NOTREACHED */
}

timeout()
{

        fprintf(stderr, "couldn't contact time server\n");
        exit(1);
}