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Linux 2.6 - man page for rtime (linux section 3)

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

NAME
       rtime - get time from a remote machine

SYNOPSIS
       #include <rpc/des_crypt.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.

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>

       int use_tcp = 0;
       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 3.55 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)


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