I have a cluster of 10 virtualized ubuntu servers. For all of them, I installed the ntp-Daemon. Since I currently running some time sensitive experiments, I am interested in the offsets between my nodes.
I found that the command ntpdate can be used to obtain offsets between the machine clocks. However,running from the first node nodeA0, the command gives:
ubuntu@nodeA0:~$ sudo ntpdate -q nodeA0 nodeA1 nodeA2 nodeA3 nodeA4 nodeA5 nodeA6 nodeA7 nodeA8 nodeA9
server 192.168.1.75, stratum 3, offset -0.000016, delay 0.02570
server 192.168.1.93, stratum 3, offset -0.000190, delay 0.02725
server 192.168.1.245, stratum 3, offset -0.000390, delay 0.02623
server 192.168.1.63, stratum 2, offset -0.000917, delay 0.02646
server 192.168.1.61, stratum 3, offset 0.000015, delay 0.02692
server 192.168.1.107, stratum 2, offset -0.002031, delay 0.02669
server 192.168.1.132, stratum 3, offset -0.000462, delay 0.02655
server 192.168.1.175, stratum 3, offset -0.000317, delay 0.02719
server 192.168.1.92, stratum 3, offset -0.000237, delay 0.02638
server 192.168.1.98, stratum 3, offset -0.000586, delay 0.02786
1 Feb 10:33:21 ntpdate[3214384]: adjust time server 192.168.1.63 offset -0.000917 sec
My questions:
- As the offset gives the clock differences between the machines, I wonder, what unit that is? milliseconds or seconds? In the manpages, I couldn`t find any information regarding that.
- Asssuming the unit is milliseconds: Then I would have an offset of
0.016 ms for nodeA1 (the first). This seems too short - I read somewhere that NTP accuracy is in the magnitude of tens of milliseconds.
- Did I do anything wrong? Or what would be the optimal way to measure clock differences between two servers?
Edit: The command ntp -qd gives:
ubuntu@nodeA0:~$ ntpq -qn
remote refid st t when poll reach delay offset jitter
==============================================================================
0.ubuntu.pool.n .POOL. 16 p - 64 0 0.000 0.000 0.000
1.ubuntu.pool.n .POOL. 16 p - 64 0 0.000 0.000 0.000
2.ubuntu.pool.n .POOL. 16 p - 64 0 0.000 0.000 0.000
3.ubuntu.pool.n .POOL. 16 p - 64 0 0.000 0.000 0.000
ntp.ubuntu.com .POOL. 16 p - 64 0 0.000 0.000 0.000
*217.91.44.17 192.168.100.15 2 u 36 256 377 11.388 0.222 0.153
-162.159.200.1 10.100.8.32 3 u 81 128 377 7.829 -0.107 1.089
+80.153.195.191 192.168.100.15 2 u 92 128 377 14.382 -0.056 0.379
+144.76.43.40 213.239.239.164 3 u 109 128 377 7.119 0.331 0.440
-194.35.12.189 131.188.3.220 2 u 108 128 377 5.618 -0.213 0.192
