I have a server in a network receiving all its network information from
DHCP. The problem is that the
ntp-server being sent is not set to UTC. I want to use the configuration for
ntp found in
/etc/ntp.conf but the
DHCP information takes precedence. How can I force
ntpd to use the configuration in
/etc/ntp.conf as opposed to the one sent by
DHCP? What is the
Debian way to do this?
I suggest you edit/create /etc/dhclient.conf and uncomment the line "request" with something like this:
request subnet-mask, broadcast-address, routers, domain-name, domain-name-servers, host-name;
Especially, if "ntp-servers" is present, remove it. Under some distribution ( aka Fedora ) it is sent by default, so you have to put this line explicitely so that the default is overriden.
man dhclient.conf for extended informations.
You can also just remove this file:
/etc/dhcp/dhclient-exit-hooks.d/ntp, instead of editing your DHCP-requests. This file creates
ntp.conf.dhcp got created at a previous boot, be sure to remove it as well.
Not directly answering the question but that may come in handy.
On Debian (at least) the DHCP client is overriding the existing ntp service configuration.
It is controlled by the script
[contents from: /etc/dhcp/dhclient-exit-hooks.d/ntp] NTP_CONF=/etc/ntp.conf NTP_DHCP_CONF=/var/lib/ntp/ntp.conf.dhcp ... [hundreds of lines of scripts]
The DHCP client receive ntp servers from the DHCP server, it grabs the current ntp service configuration from NTP_CONF path and alters it to include ntp servers received over dhcp, it generates a new ntp configuration file into NTP_DHCP_CONF path, and finally it forces the ntp service to use this new configuration file.
This results in always using the ntp servers advertised over dhcp. Bypassing system configuration.
This is hard to debug if not known because the service configuration in '/etc/ntp.conf' is left untouched and is correct on visual inspection. However it is actually ignored and overridden stealthy.
You can use 'ntpq -pn' to debug what ntp servers are actually being used by the deamon.
If there IS a ntp server in your network being advertised by DHCP and you want to ignore it:
You will need to reconfigure the dhcp client in
/etc/dhclient.conf to skip the
ntp-servers dhcp option. Refer to the answer from @Oliver.
Then you can customize the system configuration in
If there WAS a ntp server advertised by DHCP at some point but not anymore:
The system ntp configuration might still be overridden by the dhcp client, forcing obsolete ntp servers advertised a long time ago. This dhcp overriding can survive for days, across
ntp service restart and
To put an end to it, you will need to remove
/var/lib/ntp/ntp.conf.dhcp and restart the ntp service on all your servers.
This is all undocumented, unexpected and hard to debug behavior. That caused me quite the headache today which is why I am documenting this in here.