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List:       busybox
Subject:    Re: ntpdate-like functionality in ntpd
From:       Miroslav Lichvar <mlichvar () redhat ! com>
Date:       2015-01-29 12:47:18
Message-ID: 20150129124718.GB9839 () localhost
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On Tue, Jan 27, 2015 at 07:27:18PM +0100, Guillermo Rodriguez Garcia wrote:
> Is there a way to make ntpd work just like ntpdate (just use the first
> response received to set the time)? This is to set the approximate
> time at boot as quickly as possible before starting other time sensitive
> services.

By default, ntpdate actually makes 4 measurements before it sets the
clock, but older versions didn't wait between queries so it appeared
like there was only one. With current versions, which use 2s polling
interval, it takes at least 6 seconds.

> The closest I can get is ntpd -nqp <server> but this seems to need
> 5 valid samples in order to set the time.

It seems it waits for the burst mode to end before it tries to select
a source. I'm not sure that is necessary.

--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -1084,7 +1084,7 @@ select_and_cluster(void)
 
        num_points = 0;
        item = G.ntp_peers;
-       if (G.initial_poll_complete) while (item != NULL) {
+       while (item != NULL) {
                double rd, offset;
 
                p = (peer_t *) item->data;


With this change ntpd -q will set the clock with just two samples,
that's about 1-2 seconds total time.

-- 
Miroslav Lichvar
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