bionic (3) rtime.3.gz

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

       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);
       }

SEE ALSO

       ntpdate(1), inetd(8)

COLOPHON

       This  page  is  part  of  release  4.15  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/.