From 4fc6a1b42403f2100db4ec62ba4ea160dcc86e9d Mon Sep 17 00:00:00 2001 From: Miroslav Lichvar Date: Mon, 28 Nov 2016 16:42:31 +0100 Subject: [PATCH] doc: update FAQ --- doc/faq.adoc | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/doc/faq.adoc b/doc/faq.adoc index 0a1ac71..41bf92e 100644 --- a/doc/faq.adoc +++ b/doc/faq.adoc @@ -148,9 +148,14 @@ network. It's better to use more than one server, three or four is usually recommended as the minimum, so `chronyd` can detect servers that serve false time and combine measurements from multiple sources. +If you have a network card with hardware timestamping supported on Linux, it +can be enabled by the *hwtimestamp* directive in the _chrony.conf_ file. It +should make local receive and transmit timestamps of NTP packets much more +accurate. + There are also useful options which can be set in the `server` directive, they -are `minpoll`, `maxpoll`, `polltarget`, `maxdelay`, `maxdelayratio` and -`maxdelaydevratio`. +are `minpoll`, `maxpoll`, `polltarget`, `maxdelay`, `maxdelayratio`, +`maxdelaydevratio`, and `xleave`. The first three options set the minimum and maximum allowed polling interval, and how should be the actual interval adjusted in the specified range. Their @@ -189,6 +194,16 @@ with local NTP server server ntp.local minpoll 2 maxpoll 4 polltarget 30 maxdelaydevratio 2 ---- +If your server supports the interleaved mode, the `xleave` option should be +added to the `server` directive in order to receive server's more accurate +hardware or kernel transmit timestamps. When combined with local hardware +timestamping, a sub-microsecond accuracy may be possible. An example could be + +---- +server ntp.local minpoll 2 maxpoll 2 xleave +hwtimestamp eth0 +---- + === What happened to the `commandkey` and `generatecommandkey` directives? They were removed in version 2.2. Authentication is no longer supported in the @@ -376,7 +391,8 @@ to serve time to clients in the network which support the broadcast client mode === Can `chronyd` keep the system clock a fixed offset away from real time? -This is not possible as the program currently stands. +Yes. Starting from version 3.0, an offset can be specified by the `offset` +option for all time sources in the _chrony.conf_ file. === What happens if the network connection is dropped without using ``chronyc``'s `offline` command first?