====== Network Time Protocol Daemon (ntpd) ======
===== Présentation =====
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.
===== Installation =====
<code>
root@mazarini:~# apt-get install ntp
</code>

===== Configuration /etc/ntp.conf =====
==== Configuration initiale ====
<file>
# /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
</file>
==== Choisir son serveur de référence ====
<file>
# 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
</file>
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
==== Modifications ====
<file>
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			      <
</file>
===== Commandes =====
==== Gestion du daemon ====
<code>
root@mazarini:~# /etc/init.d/ntp stop
root@mazarini:~# /etc/init.d/ntp start
root@mazarini:~# /etc/init.d/ntp restart
</code>
==== Interrogation ====
<code>
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:~#
</code>
===== Références =====
  * Choix du pool de serveurs
    * [[http://documentation.online.net/fr/serveur-dedie/reseau/information-parametres-reseau-dedibox#serveurs_ntp|Documentation online.net]]
    * [[http://www.pool.ntp.org/fr/|NTP pool project]]