There are a number of utilities available to check if NTP is doing it's job. The ntpq -p command will print out your system's current time status.
# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*cudns.cit.corne ntp0.usno.navy. 2 u 832 1024 377 43.208 0.361 2.646
LOCAL(0) LOCAL(0) 10 l 13 64 377 0.000 0.000 0.008
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The ntpdc -c loopinfo will display how far off the system time is in seconds, based upon the last time the remote server was contacted.
# ntpdc -c loopinfo offset: -0.004479 s frequency: 133.625 ppm poll adjust: 30 watchdog timer: 404 s |
ntpdc -c kerninfo will display the current remaining correction.
# ntpdc -c kerninfo pll offset: -0.003917 s pll frequency: 133.625 ppm maximum error: 0.391414 s estimated error: 0.003676 s status: 0001 pll pll time constant: 6 precision: 1e-06 s frequency tolerance: 512 ppm pps frequency: 0.000 ppm pps stability: 512.000 ppm pps jitter: 0.0002 s calibration interval: 4 s calibration cycles: 0 jitter exceeded: 0 stability exceeded: 0 calibration errors: 0 |
A slightly more different version of ntpdc -c kerninfo is ntptime
# ntptime ntp_gettime() returns code 0 (OK) time c35e2cc7.879ba000 Thu, Nov 13 2003 11:16:07.529, (.529718), maximum error 425206 us, estimated error 3676 us ntp_adjtime() returns code 0 (OK) modes 0x0 (), offset -3854.000 us, frequency 133.625 ppm, interval 4 s, maximum error 425206 us, estimated error 3676 us, status 0x1 (PLL), time constant 6, precision 1.000 us, tolerance 512 ppm, pps frequency 0.000 ppm, stability 512.000 ppm, jitter 200.000 us, intervals 0, jitter exceeded 0, stability exceeded 0, errors 0. |
Yet another way to see how well NTP is working is with the ntpdate -d command. This will contact an NTP server and determine the time difference but not change your system's time.
# ntpdate -d 132.236.56.250
13 Nov 14:43:17 ntpdate[29631]: ntpdate 4.1.1c-rc1@1.836 Thu Feb 13 12:17:20 EST 2003 (1)
transmit(132.236.56.250)
receive(132.236.56.250)
transmit(132.236.56.250)
receive(132.236.56.250)
transmit(132.236.56.250)
receive(132.236.56.250)
transmit(132.236.56.250)
receive(132.236.56.250)
transmit(132.236.56.250)
server 132.236.56.250, port 123
stratum 2, precision -17, leap 00, trust 000
refid [192.5.41.209], delay 0.06372, dispersion 0.00044
transmitted 4, in filter 4
reference time: c35e5998.4a46cfc8 Thu, Nov 13 2003 14:27:20.290
originate timestamp: c35e5d55.d69a6f82 Thu, Nov 13 2003 14:43:17.838
transmit timestamp: c35e5d55.d16fc9bc Thu, Nov 13 2003 14:43:17.818
filter delay: 0.06522 0.06372 0.06442 0.06442
0.00000 0.00000 0.00000 0.00000
filter offset: 0.000036 0.001020 0.000527 0.000684
0.000000 0.000000 0.000000 0.000000
delay 0.06372, dispersion 0.00044
offset 0.001020
13 Nov 14:43:17 ntpdate[29631]: adjust time server 132.236.56.250 offset 0.001020 sec
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If you want actually watch the system synchronize you can use ntptrace.
# ntptrace 132.236.56.250 cudns.cit.cornell.edu: stratum 2, offset -0.003278, synch distance 0.02779 dtc-truetime.ntp.aol.com: stratum 1, offset -0.014363, synch distance 0.00000, refid 'ACTS' |
If you need your system time synchronized immediately you can use the ntpdate remote-servername to force a synchronization. No waiting!
# ntpdate 132.236.56.250 13 Nov 14:56:28 ntpdate[29676]: adjust time server 132.236.56.250 offset -0.003151 sec |