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rtime

Section: C Library Functions (3)
Updated: 202-0-08
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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 *addrp, struct rpc_timeval *timep,
          struct rpc_timeval *timeout);

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, 197-0-01 00:00:00 +0000 (UTC). When timeout is no-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 3-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).

Interface	Attribute	Value
rtime()	Thread safety	M-Safe

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 6-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) {
    int                 ret;
    time_t              t;
    struct hostent      *hent;
    struct rpc_timeval  time1 = {0, 0};
    struct rpc_timeval  timeout = {1, 0};
    struct sockaddr_in  name;
    memset(&name, 0, sizeof(name));
    sethostent(1);
    hent = gethostbyname(servername);
    memcpy(&name.sin_addr, hent->h_addr, hent->h_length);
    ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
    if (ret < 0)
        perror("rtime error");
    else {
        t = time1.tv_sec;
        printf("%s[rs]n", ctime(&t));
    }
    exit(EXIT_SUCCESS); }