rtime(3)

NAME#

rtime - get time from a remote machine

LIBRARY#

Standard C library (libc, -lc)

SYNOPSIS#

#include <rpc/auth_des.h>

int rtime(struct sockaddr_in *\naddrp\n, struct rpc_timeval *\ntimep\n,\n
\n          struct rpc_timeval *\ntimeout\n);

DESCRIPTION#

This function uses the Time Server Protocol as described in RFC 868 to obtain the time from a remote machine.

The Time Server Protocol gives the time in seconds since 00:00:00 UTC, 1 Jan 1900, and this function subtracts the appropriate constant in order to convert the result to seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

When timeout is non-NULL, the udp/time socket (port 37) is used. Otherwise, the tcp/time socket (port 37) is used.

RETURN VALUE#

On success, 0 is returned, and the obtained 32-bit time value is stored in timep->tv_sec. In case of error -1 is returned, and errno is set to indicate the error.

ERRORS#

All errors for underlying functions (sendto(2), poll(2), recvfrom(2), connect(2), read(2)) can occur. Moreover:

EIO

The number of returned bytes is not 4.

ETIMEDOUT

The waiting time as defined in timeout has expired.

ATTRIBUTES#

For an explanation of the terms used in this section, see attributes(7).

NOTES#

Only IPv4 is supported.

Some in.timed versions support only TCP. Try the example program with use_tcp set to 1.

BUGS#

rtime() in glibc 2.2.5 and earlier does not work properly on 64-bit machines.

EXAMPLES#

This example requires that port 37 is up and open. You may check that the time entry within /etc/inetd.conf is not commented out.

The program connects to a computer called "linux". Using "localhost" does not work. The result is the localtime of the computer "linux".

#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <rpc/auth_des.h>
static int use_tcp = 0;
static const char servername[] = "linux";
int
main(void)
{
\n
    int                 ret;
\n
    time_t              t;
\n
    struct hostent      *hent;
\n
    struct rpc_timeval  time1 = {0, 0};
\n
    struct rpc_timeval  timeout = {1, 0};
\n
    struct sockaddr_in  name;
\n
    memset(&name, 0, sizeof(name));
\n
    sethostent(1);
\n
    hent = gethostbyname(servername);
\n
    memcpy(&name.sin_addr, hent->h_addr, hent->h_length);
\n
    ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
\n
    if (ret < 0)
\n
        perror("rtime error");
\n
    else {
\n
        t = time1.tv_sec;
\n
        printf("%s\n", ctime(&t));
\n
    }
\n
    exit(EXIT_SUCCESS);
}

SEE ALSO#

ntpdate(1), inetd(8)