Manpages - rtime.3

rtime - get time from a remote machine

  #include <rpc/auth_des.h>

  int rtime(struct sockaddr_in *addrp, struct rpc_timeval *timep,
   struct rpc_timeval *timeout);

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.

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.

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.

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

Only IPv4 is supported.

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

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

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);
  }

*ntpdate*(1), *inetd*(8)

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