When running ntpd on your server, you can check the time difference between your local system and its configured NTP servers using the ntpq utility:

ntpq -p

This will display a table showing the time offset (in milliseconds) between your server and each NTP peer in the offset column.

For a one-time comparison with a specific NTP server like ntp.ubuntu.com:

ntpdate -q ntp.ubuntu.com

Sample output:

server 91.189.94.4, stratum 2, offset 0.003647, delay 0.04618
25 Apr 16:23:44 ntpdate[1234]: adjust time server 91.189.94.4 offset 0.003647 sec

To see your server's current time drift and synchronization status:

ntpstat

For more detailed synchronization information:

ntptime

If using chrony instead of ntpd:

chronyc tracking
chronyc sources

Here's a bash script to log time differences periodically:

#!/bin/bash
while true; do
    offset=$(ntpdate -q ntp.ubuntu.com | grep offset | awk '{print $10}')
    echo "$(date) - Time offset: $offset seconds" >> /var/log/ntp_offset.log
    sleep 3600
done

For significant time differences (> 5 minutes), you may need to force a time update:

service ntpd stop
ntpdate ntp.ubuntu.com
service ntpd start

---

When you need to verify the time synchronization between your local server and an NTP server like ntp.ubuntu.com, the ntpq utility (included with ntpd) provides the most accurate comparison:

ntpq -pn

This will display output similar to:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*time.cloudflare 10.11.12.13     3 u   12   64  377    1.234   -0.567   0.891
 ntp.ubuntu.com  .POOL.          16 u    - 1024    0    0.000    0.000   0.000

Focus on these columns in the output:

• offset: The time difference in milliseconds between your server and the NTP server
• delay: Network round-trip time to the server
• jitter: Variation in network latency

If you need a quick one-time comparison without relying on the running ntpd daemon:

ntpdate -q ntp.ubuntu.com

Sample output:

server 91.189.89.198, stratum 2, offset 0.002345, delay 0.14567
28 Apr 15:20:21 ntpdate[1234]: adjust time server 91.189.89.198 offset 0.002345 sec

For regular monitoring, you can create a simple bash script:

#!/bin/bash
OFFSET=$(ntpq -pn | awk '/^*/ {print $9}')
THRESHOLD=100 # milliseconds
if (( $(echo "$OFFSET > $THRESHOLD" | bc -l) )); then
  echo "WARNING: Time offset too large - $OFFSET ms"
  exit 1
else
  echo "Time sync OK - Offset: $OFFSET ms"
  exit 0
fi

Remember that:

• Network conditions affect measurement accuracy
• Large offsets may indicate ntpd hasn't fully synchronized yet
• Firewalls can interfere with NTP traffic (UDP port 123)

When using ntp.ubuntu.com (part of the NTP Pool Project):

• The actual server IP may change due to DNS rotation
• Multiple servers are used for redundancy
• Consider using specific pool zone servers (e.g., 0.ubuntu.pool.ntp.org) for better consistency