Can I use Network Time Protocol (NTP) on my RightScale EC2 servers?

Enabling the Independent Wallclock

Issue the following command:

# echo 1 > /proc/sys/xen/independent_wallclock

Overriding the value in /proc/sys/xen/independent_wallclock disables sync with the clock on the physical machine (default).

Important! The drift time will remain after running ntpdate or ntpd until the binary value in independent_wallclock is set to 1.

Installing NTP

If you don't have NTP installed on your instance you must install it first:

# apt-get -y install ntp || yum -y install ntp

Using ntpdate

For a once off sync with a remote NTP server, you can use ntpdate, e.g.:

root@sandbox:~# ntpdate ntp.nasa.gov time-b.nist.gov
30 Jun 04:05:58 ntpdate[19740]: adjust time server 198.123.30.132 offset -0.001006 sec

Notice the time adjustment. If a large drift remains after running ntpdate twice, the independent wallclock has not been enabled.

Using ntpd

For regular sync with remote NTP servers, use ntpd.

#!/bin/bash -ex
if grep 'server ntp.ubuntu.com' /etc/ntp.conf > /dev/null 2>&1; then
    sed -i 's/server ntp.ubuntu.com/#server ntp.ubuntu.com/g' /etc/ntp.conf
fi
cat <<EOF>> /etc/ntp.conf
server time.rightscale.com
server pool.ntp.org
EOF

service ntp restart || service ntpd restart

Example service restart showing the initialization of ntpd then a subsequent sync according to the frequency in the configuration:

root@sandbox:~# service ntp restart; tail -f /var/log/messages
 * Stopping NTP server ntpd                                                                                                                                                                                                                 [ OK ]
 * Starting NTP server ntpd                                                                                                                                                                                                                 [ OK ]
Jun 30 04:11:16 sandbox ntpd[20173]: ntpd 4.2.4p8@1.1612-o Tue Apr 19 07:08:18 UTC 2011 (1)
Jun 30 04:11:16 sandbox ntpd[20174]: precision = 1.000 usec
Jun 30 04:11:16 sandbox ntpd[20174]: Listening on interface #0 wildcard, 0.0.0.0#123 Disabled
Jun 30 04:11:16 sandbox ntpd[20174]: Listening on interface #1 wildcard, ::#123 Disabled
Jun 30 04:11:16 sandbox ntpd[20174]: Listening on interface #2 lo, 127.0.0.1#123 Enabled
Jun 30 04:11:16 sandbox ntpd[20174]: Listening on interface #3 eth0, 10.161.110.239#123 Enabled
Jun 30 04:11:16 sandbox ntpd[20174]: Listening on interface #4 lo, ::1#123 Enabled
Jun 30 04:11:16 sandbox ntpd[20174]: Listening on interface #5 eth0, fe80::1031:3fff:fe01:6d01#123 Enabled
Jun 30 04:11:16 sandbox ntpd[20174]: kernel time sync status 2040
Jun 30 04:11:16 sandbox ntpd[20174]: frequency initialized 17.284 PPM from /var/lib/ntp/ntp.drift
Jun 30 04:15:34 sandbox ntpd[20174]: synchronized to 174.129.253.100, stratum 2
Jun 30 04:15:34 sandbox ntpd[20174]: kernel time sync status change 2001