rtime(3) — Linux manual page


rtime(3)                Library Functions Manual                rtime(3)

NAME         top

       rtime - get time from a remote machine

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <rpc/auth_des.h>

       int rtime(struct sockaddr_in *addrp, struct rpc_timeval *timep,
                 struct rpc_timeval *timeout);

DESCRIPTION         top

       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         top

       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 to indicate the error.

ERRORS         top

       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.

              The waiting time as defined in timeout has expired.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ rtime()                             │ Thread safety │ MT-Safe │

NOTES         top

       Only IPv4 is supported.

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

BUGS         top

       rtime() in glibc 2.2.5 and earlier does not work properly on
       64-bit machines.

EXAMPLES         top

       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 <errno.h>
       #include <netdb.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>
       #include <time.h>

       #include <rpc/auth_des.h>

       static int use_tcp = 0;
       static const char servername[] = "linux";

           int                 ret;
           time_t              t;
           struct hostent      *hent;
           struct rpc_timeval  time1 = {0, 0};
           struct rpc_timeval  timeout = {1, 0};
           struct sockaddr_in  name;

           memset(&name, 0, sizeof(name));
           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 {
               t = time1.tv_sec;
               printf("%s\n", ctime(&t));


SEE ALSO         top

       ntpdate(1), inetd(8)

Linux man-pages (unreleased)     (date)                         rtime(3)