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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.  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->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); }