In fact I have a time stamp project, so the time must be accurate and any manual change (By hacker for example) must be fixed rapidly. I can do that by ntpdate in cron and that permit a refresh on each minute or using ntp client.
However, ntp client doesn't work in the right manner. According to the last comment when is always less than poll which is not the case. In addition, when I change the time (date -s hh:mm:ss) with less than 1000 s difference, the adjustment did not happen in the next 64s.
I use ubuntu 10.10 and this is my ntp.conf file if needed:
# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help
# Enable this if you want statistics to be logged.
statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable
# You do need to talk to an NTP server or two (or three).
# Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for
# details. The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions>
# might also be helpful.
# Note that "restrict" applies to both servers and clients, so a configuration
# that might be intended to block requests from certain clients could also end
# up blocking replies from your own upstream servers.
# By default, exchange time with everybody, but don't allow configuration.
restrict -4 default kod notrap nomodify nopeer noquery
restrict -6 default kod notrap nomodify nopeer noquery
# Local users may interrogate the ntp server more closely.
# Clients from this (example!) subnet have unlimited access, but only if
# cryptographically authenticated.
#restrict 192.168.123.0 mask 255.255.255.0 notrust
# If you want to provide time to your local subnet, change the next line.
# (Again, the address is an example only.)
# If you want to listen to time broadcasts on your local subnet, de-comment the
# next lines. Please do this only if you trust everybody on the network!
Thank's for help