RTIME(3) Linux Programmer's Manual RTIME(3)

NAME
       rtime - get time from a remote machine

SYNOPSIS
       #include 

       int rtime(struct sockaddrin *addrp, struct rpctimeval *timep,
                 struct rpctimeval *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.  Oth‐
       erwise, 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->tvsec.   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.

NOTES
       Only IPv4 is supported.

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

       Libc5 uses the prototype
       int rtime(struct sockaddrin *, struct timeval *, struct timeval *);
       and requires  instead of .

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 
       #include 
       #include 
       #include 
       #include 
       #include 
       #include 

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

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

           memset(&name, 0, sizeof(name));
           sethostent(1);
           hent = gethostbyname(servername);
           memcpy(&name.sinaddr, hent->haddr, hent->hlength);

           ret = rtime(&name, &time1, usetcp ? NULL : &timeout);
           if (ret < 0)
               perror("rtime error");
           else {
            timet t = time1.tvsec;
               printf("%s\n", ctime(&t));
           }

           exit(EXITSUCCESS);
       }

SEE ALSO
       ntpdate(1), inetd(8)

COLOPHON
       This  page  is  part of release 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



GNU                               2012-08-03                          RTIME(3)