rtime

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 or-
       der 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 at-
       tributes(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 ma-
       chines.

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 5.05 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/.

GNU                               2019-03-06                          RTIME(3)