ntpd est un daemon qui permet de garder sa machine à l'heure en se synchronisant sur des serveurs de temps. A noté que les machines virtuelles n'ont pas besoin de se synchroniser puisqu'elles utilisent l'horloge de leur hôte.

root@mazarini:~# apt-get install ntp

# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help

driftfile /var/lib/ntp/ntp.drift


# Enable this if you want statistics to be logged.
#statsdir /var/log/ntpstats/

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).
#server ntp.your-provider.example

# pool.ntp.org maps to about 1000 low-stratum NTP servers.  Your server will
# pick a different set every time it starts up.  Please consider joining the
# pool: <http://www.pool.ntp.org/join.html>
server 0.debian.pool.ntp.org iburst
server 1.debian.pool.ntp.org iburst
server 2.debian.pool.ntp.org iburst
server 3.debian.pool.ntp.org iburst


# 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.
restrict 127.0.0.1
restrict ::1

# 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.)
#broadcast 192.168.123.255

# 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!
#disable auth
#broadcastclient

# pool.ntp.org maps to about 1000 low-stratum NTP servers.  Your server will
# pick a different set every time it starts up.  Please consider joining the
# pool: <http://www.pool.ntp.org/join.html>
server 0.fr.pool.ntp.org iburst dynamic
server 1.fr.pool.ntp.org iburst dynamic
server 2.fr.pool.ntp.org iburst dynamic
server 3.fr.pool.ntp.org iburst dynamic
server ntp.online.net    iburst dynamic

Il faut choisir des serveurs proche de chez soi. Souvent, ce ne sont pas des machines mais des pools de machines qui tournent.

J'ai choisi de prendre les serveurs ntp de mon hébergeur et les 4 pools français. Il y a des pools définis par zone géographique.

La machine ntp.online.net correspond à un pool de machines.

iburst : interroger les serveurs plusieurs fois en cas de non réponse

dynamic : ne pas black-lister les serveurs indisponible

server ntp.online.net    iburst dynamic			      |	pool 0.debian.pool.ntp.org iburst
server 0.fr.pool.ntp.org iburst dynamic			      |	pool 1.debian.pool.ntp.org iburst
server 1.fr.pool.ntp.org iburst dynamic			      |	pool 2.debian.pool.ntp.org iburst
server 2.fr.pool.ntp.org iburst dynamic			      |	pool 3.debian.pool.ntp.org iburst
server 3.fr.pool.ntp.org iburst dynamic			      <

root@mazarini:~# /etc/init.d/ntp stop
root@mazarini:~# /etc/init.d/ntp start
root@mazarini:~# /etc/init.d/ntp restart

root@mazarini:~# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 gw-01.darksky.i 213.251.128.249  2 u   48   64    1    4.463    2.915   0.000
 ns0.luns.net.uk 158.43.192.66    2 u   47   64    1   22.373   -0.584   0.000
 62-210-28-176.r 84.255.209.79    4 u   46   64    1    0.452   -0.475   0.000
 ntp-2.arkena.ne 193.190.230.65   2 u   45   64    1    0.916    0.336   0.000
 ntp1.online.net 145.238.203.14   2 u   44   64    1    0.293    2.246   0.000
root@mazarini:~#

• Choix du pool de serveurs
  • Documentation online.net
  • NTP pool project