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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  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);
   }

SEE ALSO

   ntpdate(1), inetd(8)

COLOPHON

   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at
   https://www.kernel.org/doc/man-pages/.



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