NTPD – How to Prevent Listening on 0.0.0.0:123

debianlinuxntpd

ntpd listens on numerous interfaces by default, I only want it to listen on 127.0.0.1:123 since I only want the localhost to sync the time.

How to do that, I tried by editing /etc/default/ntp on Debian Wheezy:

NTPD_OPTS='-4 -I 127.0.0.1'

But it still listens globally on 0.0.0.0:123

Any ideas?

Best Answer

Remove all -I or --interface options from /etc/default/ntp and insert the following into your /etc/ntp.conf:

interface ignore wildcard
interface listen 127.0.0.1
interface listen ::1
# NOTE: if you want to update your time using remote machines,
# add at least one remote interface address:
#interface listen 2001:db8::1
#interface listen 192.0.2.1

An excerpt from the ntpd(1) manual page about the -i option:

This option also implies not opening other addresses, except wildcard and localhost. Please consider using the configuration file interface command, which is more versatile.

See also the Debian manual page (I could not find it in Arch Linux one) of ntp.conf(5).

Related Topic