docs: Add info about mode7 requirement for ntpd

Since ntpd-4.2.7p230 "mode 7" requests are ignored by default, and
that's what ntpd plugin uses currently. The ntp daemon must be
explicitly configured to enable mode7 requests.
This patch adds short information about that to collectd.conf manpage.

Related to collectd/collectd#932

Signed-off-by: Jakub Jankowski <shasta@toxcorp.com>

diff --git a/src/collectd.conf.pod b/src/collectd.conf.pod
index f4bd32a..d856d21 100644 (file)
--- a/src/collectd.conf.pod
+++ b/src/collectd.conf.pod
@@ -3751,6 +3751,18 @@ Default: C<Collectd notify: %s@%s>
 
 =head2 Plugin C<ntpd>
 
+The C<ntpd> plugin collects per-peer ntpd data such as time offset and time
+dispersion.
+
+For talking to B<ntpd>, it mimics what the B<ntpdc> control program does on
+wire - using B<mode 7> specific requests. This mode is deprecated with
+newer B<ntpd> releases (4.2.7p230 and later). For the C<ntpd> plugin to work
+correctly with them, the ntp daemon must be explicitly configured to
+enable B<mode 7> (which is disabled by default). Refer to the I<ntp.conf(5)>
+manual page for details.
+
+Available configuration options for the C<ntpd> plugin:
+
 =over 4
 
 =item B<Host> I<Hostname>