NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | NOTES | BUGS | EXAMPLE | SEE ALSO | COLOPHON

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

NAME         top

       rtime - get time from a remote machine

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 appropriately.

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.

       ETIMEDOUT
              The waiting time as defined in timeout has expired.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌──────────┬───────────────┬─────────┐
       │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.

       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         top

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

EXAMPLE         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 <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         top

       ntpdate(1), inetd(8)

COLOPHON         top

       This page is part of release 4.10 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                              2015-03-02                         RTIME(3)