I looked up the details of the right con ... / 2013-12-17

I looked up the details of the right configuration for ntpd to allow a reset of the packet counters without restarting ntpd for the ntp server project. Relevant part of /etc/ntp.conf:

keys /etc/ntp/ntp.keys
trustedkey 10
requestkey 10
controlkey 10

And in /etc/ntp/ntp.keys is one key 10. And it works:

ntpdc> syss
time since restart:     12
time since reset:       12
packets received:       10
packets processed:      8
current version:        8
previous version:       0
..
ntpdc> reset sys
Keyid: 10
MD5 Password: 
done!
ntpdc> syss
time since restart:     19
time since reset:       3
packets received:       2
packets processed:      1
current version:        1
previous version:       0
..

Learned from How do I configure remote administration - ntp faq and miscellaneous commands and options - ntpd.