RTIME(3)                            Linux Programmer's Manual                            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
   Multithreading (see pthreads(7))
       The rtime() function is thread-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 3.74 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 http://www.kernel.org/doc/man-pages/.



GNU                                         2014-05-28                                   RTIME(3)