man3/rtime.3

.\" Copyright 2003 walter harms (walter.harms@informatik.uni-oldenburg.de)
.\"
.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
.\" Distributed under GPL
.\" %%%LICENSE_END
.\"
.\" Modified 2003-04-04 Walter Harms
.\" <walter.harms@informatik.uni-oldenburg.de>
.\"
.\" Slightly polished, aeb, 2003-04-06
.\"
.TH RTIME 3 2020-06-09 "GNU" "Linux Programmer's Manual"
.SH NAME
rtime \- get time from a remote machine
.SH SYNOPSIS
.nf
.B "#include <rpc/auth_des.h>"
.PP
.BI "int rtime(struct sockaddr_in *" addrp ", struct rpc_timeval *" timep ,
.BI "          struct rpc_timeval *" timeout );
.fi
.SH DESCRIPTION
This function uses the Time Server Protocol as described in
RFC\ 868 to obtain the time from a remote machine.
.PP
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).
.PP
When
.I timeout
is non-NULL, the udp/time socket (port 37) is used.
Otherwise, the tcp/time socket (port 37) is used.
.SH RETURN VALUE
On success, 0 is returned, and the obtained 32-bit time value is stored in
.IR timep\->tv_sec .
In case of error \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
All errors for underlying functions
.RB ( sendto (2),
.BR poll (2),
.BR recvfrom (2),
.BR connect (2),
.BR read (2))
can occur.
Moreover:
.TP
.B EIO
The number of returned bytes is not 4.
.TP
.B ETIMEDOUT
The waiting time as defined in timeout has expired.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR rtime ()
T}	Thread safety	MT-Safe
.TE
.SH NOTES
Only IPv4 is supported.
.PP
Some
.I in.timed
versions support only TCP.
Try the example program with
.I use_tcp
set to 1.
.PP
Libc5 uses the prototype
.PP
.nf
    int rtime(struct sockaddr_in *, struct timeval *, struct timeval *);
.fi
.PP
and requires
.I <sys/time.h>
instead of
.IR <rpc/auth_des.h> .
.SH BUGS
.BR rtime ()
in glibc 2.2.5 and earlier does not work properly on 64-bit machines.
.SH EXAMPLES
This example requires that port 37 is up and open.
You may check
that the time entry within
.I /etc/inetd.conf
is not commented out.
.PP
The program connects to a computer called "linux".
Using "localhost" does not work.
The result is the localtime of the computer "linux".
.PP
.EX
#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\en", ctime(&t));
    }

    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.\" .BR netdate (1),
.BR ntpdate (1),
.\" .BR rdate (1),
.BR inetd (8)