Configuración Server  NTP en Debian

Instalar el paquete ntp

#apt-get install ntp

Configurar el archivo que se encuentra en /etc/ntp.conf

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 # pick a different set every time it starts up.  Please consider joining the # pool: <http://www.south-america.pool.ntp.org> server 0.south-america.pool.ntp.org server 1.south-america.pool.ntp.org server 2.south-america.pool.ntp.org server 3.south-america.pool.ntp.org # Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for details # 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

Configuración clientes NTP en Linux

Hay que poner en el cron

#crontab -e

* */6 * * *     root /usr/sbin/ntpdate 10.10.120.87

Configuración clientes NTP en maquinas virtuales con XEN

Para poder utilizar cliente NTP sobre una maquina virtual XEN hay que modificar el parámetro del kernel y establecerlo en 1 de xen.independent_wallclock

El reloj local de una maquina XEN por default viene sincronizado con la reloj físico del host para poder utilizar y sincronizar con un servidor NTP debe modificarse el parámetro del kernel y debe de ser

#echo 1 > /proc/sys/xen/independent_wallclock

Luego editamos el archive  /etc/sysctl.conf de la maquina virtual y agregamos las siguientes lineas

# Set independent wall clock time xen.independent_wallclock=1

Luego en el cron colocamos que se sincronice cada 6 hs con el servidor nuestro

* */6 * * *     root /usr/sbin/ntpdate 10.10.120.87