RTIME(3)                  (2020-12-21)                   RTIME(3)

     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 sec-
          onds 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).  allbox; lb lb lb l l l.
          Interface Attribute Value T{ rtime() T}   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.

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

     Page 1                         GNU              (printed 5/25/22)

     RTIME(3)                  (2020-12-21)                   RTIME(3)

     EXAMPLES
          This example requires that port 37 is up and open.  You may
          check that the time entry within /etc/inetd.conf is not com-
          mented 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);
          }

     SEE ALSO
          ntpdate(1), inetd(8)

     COLOPHON
          This page is part of release 5.10 of the Linux man-pages
          project.  A description of the project, information about
          reporting bugs, and the latest version of this page, can be

     Page 2                         GNU              (printed 5/25/22)

     RTIME(3)                  (2020-12-21)                   RTIME(3)

          found at https://www.kernel.org/doc/man-pages/.

     Page 3                         GNU              (printed 5/25/22)