RTIME

NAME

rtime - get time from a remote machine

SYNOPSIS

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 midnight 1900-01-01, and this function subtracts the appropriate constant in order to convert the result to seconds since midnight 1970-01-01, the Unix epoch.

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, poll, recvfrom, connect, read) can occur. Moreover:

ETIMEDOUT: The waiting time as defined in timeout has expired.
EIO: The number of returned bytes is not 4.

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

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

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

  memset((char *)&name, 0, sizeof(name));
  sethostent(1);
  hent = gethostbyname(servername);
  memcpy((char *)&name.sin_addr, hent->h_addr, hent->h_length); 

  ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
  if (ret < 0)
    perror("rtime error");
  else
    printf("%s", ctime((time_t *)&time1.tv_sec));

  return 0;
}

NOTES

Only IPV4 is supported.

Some in.timed versions only support TCP. Try the above 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 does not work properly on 64bit machines.