NTP
Keeping time is important. Especially when debugging an issue between servers. It is a pain comparing logfiles with a time skew. For that reason we will configure two NTP servers that all clients will synchronize their time to.
Configuring a redundant NTP server does not really make any sense. The DHCP server sends option ntp-servers to the DHCP clients, so if one NTP server is down, then the other will get the request instead.
Network
The NTP servers will have fixed IP-addresses. That is configured in the DHCP servers list of statically assigned IP-adresses by using the Domains MAC address.
- 192.168.1.40 ntp01
- 192.168.1.41 ntp02
Software
Disable the preinstalled ntp server
systemctl disable systemd-timesyncd
Set the Time
apt-get install sntp sntp pool.ntp.org hwclock --systohc
Install the NTP Daemon
apt-get install chrony
Configuration
Make sure chrony accepts connections from other hosts. Add the following line to /etc/chrony/chrony.conf
allow all
Restart chrony
service chrony restart
Debugging
Kiss of Death
The NTP-servers may run into to a synchronization loop. KoD (Kiss of Death) will be logged.
ntp01 /var/log/syslog
Jan 30 06:39:30 ntp01 ntpd[464]: receive: KoD packet from 192.168.1.41 has inconsistent xmt/org/rec timestamps. Ignoring.
ntp02 /var/log/syslog
Jan 30 07:04:15 ntp02 ntpd[511]: receive: KoD packet from 192.168.1.40 has inconsistent xmt/org/rec timestamps. Ignoring.
While getting its IP-address from a DHCP-server, the system will also ask the DHCP-server for any available NTP-servers. This causes the NTP server to synchronize time against the other NTP-server and vice versa, which again causes them to loose track of time. The solution is to tell the DHCP-client to not request the NTP information from the DHCP-server.
Make the following change in /etc/dhcp/dhclient.conf
request subnet-mask, broadcast-address, time-offset, routers,
domain-name, domain-name-servers, domain-search, host-name,
dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn, dhcp6.sntp-servers,
netbios-name-servers, netbios-scope, interface-mtu,
#rfc3442-classless-static-routes, ntp-servers;
rfc3442-classless-static-routes;