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RTIME

Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME

rtime - get time from a remote machine

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, 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 appropriately.

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	MT-Safe

NOTES

Only IPv4 is supported.

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

Libc5 uses the prototype

    int rtime(struct sockaddr_in *, struct timeval *, struct timeval *);

and requires <sys/time.h> instead of <rpc/auth_des.h>.

BUGS

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

EXAMPLE

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 <stdio.h> #include <stdlib.h> #include <errno.h> #include <string.h> #include <time.h> #include <rpc/auth_des.h> #include <netdb.h>

static int use_tcp = 0; static char *servername = "linux";

int main(void) {
    struct sockaddr_in name;
    struct rpc_timeval time1 = {0,0};
    struct rpc_timeval timeout = {1,0};
    struct hostent *hent;
    int ret;

    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 {
        time_t t = time1.tv_sec;
        printf("%s\n", ctime(&t));
    }

exit(EXIT_SUCCESS); }

COLOPHON

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