Zeitserver einrichten

Mittels NTP Nutzen wir einen Standard zur Synchronisierung aller Uhren in unserem Netzwerk. NTP wurde als RFC 958 definiert um eine zuverlässige Zeitgabe über Netzwerke mit variabler Paketlaufzeit zu ermöglichen und bekam von der Internet Assigned Numbers Authority den UDP-Ports 123 zugewiesen.

yum install ntp

Die Konfiguration unseres Zeitservers erfolgt über die Datei /etc/ntp.conf:

# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
restrict default kod nomodify notrap nopeer noquery
 
# Permit all access over the loopback interface.  This could
# be tightened as well, but to do so would effect some of
# the administrative functions.
restrict 127.0.0.1 
restrict -6 ::1
 
# Hosts on local network are less restricted.
restrict 192.168.100.0 mask 255.255.255.0 nomodify notrap
 
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
server 0.centos.pool.ntp.org
server 1.centos.pool.ntp.org
server 2.centos.pool.ntp.org
 
#broadcast 192.168.1.255 key 42         # broadcast server
#broadcastclient                        # broadcast client
#broadcast 224.0.1.1 key 42             # multicast server
#multicastclient 224.0.1.1              # multicast client
#manycastserver 239.255.254.254         # manycast server
#manycastclient 239.255.254.254 key 42  # manycast client
#manycastserver 192.168.10.255
 
# Undisciplined Local Clock. This is a fake driver intended for backup
# and when no outside source of synchronized time is available. 
server  127.127.1.0
fudge   127.127.1.0 stratum 10
 
# Drift file.  Put this in a directory which the daemon can write to.
# No symbolic links allowed, either, since the daemon updates the file
# by creating a temporary in the same directory and then rename()'ing
# it to the file.
driftfile /var/lib/ntp/drift
 
# Key file containing the keys and key identifiers used when operating
# with symmetric key cryptography. 
keys /etc/ntp/keys
 
# Specify the key identifiers which are trusted.
#trustedkey 4 8 42
 
# Specify the key identifier to use with the ntpdc utility.
#requestkey 8
 
# Specify the key identifier to use with the ntpq utility.
#controlkey 8
restrict 0.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
restrict 1.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
restrict 2.centos.pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
#Specify alternate log file
logfile /var/log/ntp.log

Der NTP Server wird idealerweise mittels DHCP verbreitet. Dazu muss di eDatei /etc/dhcpd.conf angepasst werden:

option ntp-servers   192.168.100.1;   #IP Adresse anpassen

Abschließend restarten wir unseren DHCP-Server.

service dhcpd restart

service ntpd start

Damit der Zeitserver ntpd automatisch bei jedem Systemstart startet, kann die Einrichtung eines Start-Scriptes über folgenden Befehl erreicht werden:

chkconfig ntpd on

Mit dem Befehl

watch ntpq -np 

können wir uns abschließend den Status unseres Timeservers anzeigen lassen