How to chroot ntp in Debian

Here are few simple steps to chroot ntp in debian. Add the following to file /usr/local/sbin/chroot-ntp and execute (alternatively you can download script from bitbucket site here):

#!/bin/bash

/etc/init.d/ntp stop

rootfs=/var/chroot/ntp
mkdir -p $rootfs/{etc,var/lib/ntp,var/log}

mv /etc/ntp.conf $rootfs/etc
ln -s $rootfs/etc/ntp.conf /etc/ntp.conf

if [ -e /var/lib/ntp/ntp.drift ]; then
    mv /var/lib/ntp/ntp.drift $rootfs/var/lib/ntp
fi
ln -s $rootfs/var/lib/ntp/ntp.drift \
    /var/lib/ntp/ntp.drift
chown -R ntp:ntp $rootfs/var/lib/ntp

mv /var/log/ntpstats $rootfs/var/log
ln -s $rootfs/var/log/ntpstats /var/log/ntpstats
chown -R ntp:ntp $rootfs/var/log/ntpstats

sed -e "s,'-g','-4 -i /var/chroot/ntp -g'," \
    /etc/default/ntp > /tmp/x && \
    mv /tmp/x /etc/default/ntp

sed -e "s,restrict -6,#restrict -6," \
    -e "s,restrict ::1,#restrict ::1," \
    /etc/ntp.conf > /tmp/x && \
    mv /tmp/x /etc/ntp.conf

/etc/init.d/ntp start

Verify that ntp uses the chroot (file /etc/default/ntp):

NTPD_OPTS='-4 -i /var/chroot/ntp -g'

Debian NTP Server

Let start by installing few packages:

apt-get -y install ntp ntpdate

The options passed to ntp daemon are set in /etc/default/ntp file. We are interested to turn off ipv6 for now:

NTPD_OPTS='-4 -g'

As well we are going restrict ntp daemon for use ipv4 only (file /etc/ntp.conf):

# 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

Restart ntp daemon so the changes take place:

/etc/init.d/ntp restart

Look which servers it uses for synchronization:

ntpq -4p

Client

Install ntpdate package:

apt-get -y install ntpdate

You can sync the client with you ntp server by issuing the following command (I assume your local htp server resolves to ntp.dev.local):

ntpdate -p 2 ntp.dev.local

Consider have a look at the following post (you just need to substitute the ntp server name with yours).

Sync time with external server in Debian

You can synchronize your local computer time with external time servers. You need install ntpdate:

apt-get -y install ntpdate

Try update your time manually:

deby:~# ntpdate pool.ntp.org
12 Jun 00:04:16 ntpdate[1903]: step time server 62.80.187.114 offset -291.468062 sec

Here is a script that syncs the time with external server, adjusts clock drift and finally sets the hardware clock to current system time (file /usr/local/sbin/sync-time).

#!/bin/bash

server=pool.ntp.org

# Sleep a random amount, not greater than 2 minutes
sleep_time=$(($RANDOM % 120))

echo "Sleeping for $sleep_time seconds..."
/bin/sleep $sleep_time

# Sync the time with external server
echo "Sync time with $server."
/usr/sbin/ntpdate -s $server || exit 1

# Adjusts clock drift
/sbin/hwclock --adjust

# Set the hardware clock to current system time
/sbin/hwclock --systohc

Here we are going to schedule a cron job on system startup (file /usr/local/sbin/sync-time, symbolic link from /etc/cron.d/sync-time):

#
# Regular cron job for time synchronization
#
PATH=/usr/local/sbin
HOME=/
LOG=/dev/null

# Every 23 hours, e.g. 2:11, 13:11, etc
11 */23 * * * root test -x /usr/local/sbin/sync-time && sync-time > $LOG

The next time your system restarts it will automatically synchronizes clock with external server. Please note that the system sync the time each time the network interface is up (see ntpdate script in /etc/network/if-up.d/).