doc: update chrony.conf man page for recent changes

diff --git a/doc/chrony.conf.adoc b/doc/chrony.conf.adoc
index e3b011018a37f804af849467b32392cdf49003bf..da86723be6e7db225bc5a2c6d6721e7e4fbd45e7 100644 (file)
--- a/doc/chrony.conf.adoc
+++ b/doc/chrony.conf.adoc
@@ -72,24 +72,27 @@ polling interval should not drop below 32 seconds. The default is 6 (64
 seconds), the minimum is -4 (1/16th of a second), and the maximum is 24 (6
 months). Note that intervals shorter than 6 (64 seconds) should generally not
 be used with public servers on the Internet, because it might be considered
-abuse.
+abuse. A sub-second interval will be enabled only when the server is reachable
+and the round-trip delay is shorter than 10 milliseconds, i.e. the server
+should be in a local network.
 *maxpoll* _poll_:::
 This option specifies the maximum interval between requests sent to the server
 as a power of 2 in seconds. For example, *maxpoll 9* indicates that the polling
 interval should stay at or below 9 (512 seconds). The default is 10 (1024
-seconds), the minimum is 0 (1 second), and the maximum is 24 (6 months).
+seconds), the minimum is -4 (1/16th of a second), and the maximum is 24 (6
+months).
 *iburst*:::
 With this option, the interval between the first four requests sent to the
-server will be 2 seconds instead of the interval specified by the *minpoll*
-option, which allows *chronyd* to make the first update of the clock shortly
-after start.
+server will be 2 seconds or less instead of the interval specified by the
+*minpoll* option, which allows *chronyd* to make the first update of the clock
+shortly after start.
 *burst*:::
 With this option, *chronyd* will shorten the interval between up to four
-requests to 2 seconds when it cannot get a good measurement from the server.
-The number of requests in the burst is limited by the current polling interval
-to keep the average interval at or above the minimum interval, i.e. the current
-interval needs to be at least two times longer than the minimum interval in
-order to allow a burst with two requests.
+requests to 2 seconds or less when it cannot get a good measurement from the
+server. The number of requests in the burst is limited by the current polling
+interval to keep the average interval at or above the minimum interval, i.e.
+the current interval needs to be at least two times longer than the minimum
+interval in order to allow a burst with two requests.
 *key* _ID_:::
 The NTP protocol supports a message authentication code (MAC) to prevent
 computers having their system time upset by rogue packets being sent to them.