server time.bora.net iburst
server ntp2.kornet.net iburst
server 1.kr.pool.ntp.org iburst

[root@ol8 ~]# cat /etc/chrony.conf
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
#pool 2.rhel.pool.ntp.org iburst

server time.bora.net iburst
server ntp2.kornet.net iburst
server 1.kr.pool.ntp.org iburst

# Record the rate at which the system clock gains/losses time.
driftfile /var/lib/chrony/drift

# Allow the system clock to be stepped in the first three updates
# if its offset is larger than 1 second.
makestep 1.0 3

# Enable kernel synchronization of the real-time clock (RTC).
rtcsync

# Enable hardware timestamping on all interfaces that support it.
#hwtimestamp *

# Increase the minimum number of selectable sources required to adjust
# the system clock.
#minsources 2

# Allow NTP client access from local network.
#allow 192.168.0.0/16
allow 192.168.12.0/24

# Serve time even if not synchronized to a time source.
#local stratum 10

# Specify file containing keys for NTP authentication.
keyfile /etc/chrony.keys

# Get TAI-UTC offset and leap seconds from the system tz database.
leapsectz right/UTC

# Specify directory for log files.
logdir /var/log/chrony

# Select which information is logged.
#log measurements statistics tracking

[root@ol8 ~]# systemctl start chronyd
[root@ol8 ~]# systemctl enable chronyd
Created symlink /etc/systemd/system/multi-user.target.wants/chronyd.service → /usr/lib/systemd/system/chronyd.service.

[root@ol8 ~]# timedatectl
               Local time: Tue 2024-04-02 09:43:08 KST
           Universal time: Tue 2024-04-02 00:43:08 UTC
                 RTC time: Tue 2024-04-02 00:43:08
                Time zone: Asia/Seoul (KST, +0900)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

[root@ol8 ~]# chronyc sources
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^? time.bora.net                 2   6    40    22   -395ms[ -395ms] +/- 1563ms
^? 169.254.169.123               0   7     0     -     +0ns[   +0ns] +/-    0ns
^? 169.254.169.124               0   7     0     -     +0ns[   +0ns] +/-    0ns

[root@ol8 ~]# chronyc sourcestats
Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
==============================================================================
time.bora.net               1   0     0     +0.000   2000.000   -395ms  4000ms
169.254.169.123             0   0     0     +0.000   2000.000     +0ns  4000ms
169.254.169.124             0   0     0     +0.000   2000.000     +0ns  4000ms

[root@ol8 ~]# chronyc sources -v

  .-- Source mode  '^' = server, '=' = peer, '#' = local clock.
 / .- Source state '*' = current best, '+' = combined, '-' = not combined,
| /             'x' = may be in error, '~' = too variable, '?' = unusable.
||                                                 .- xxxx [ yyyy ] +/- zzzz
||      Reachability register (octal) -.           |  xxxx = adjusted offset,
||      Log2(Polling interval) --.      |          |  yyyy = measured offset,
||                                \     |          |  zzzz = estimated error.
||                                 |    |           \
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^? time.bora.net                 2   6    40    26   -395ms[ -395ms] +/- 1563ms
^? 169.254.169.123               0   7     0     -     +0ns[   +0ns] +/-    0ns
^? 169.254.169.124               0   7     0     -     +0ns[   +0ns] +/-    0ns

[root@ol8 ~]# chronyc tracking
Reference ID    : 00000000 ()
Stratum         : 0
Ref time (UTC)  : Thu Jan 01 00:00:00 1970
System time     : 0.000000000 seconds slow of NTP time
Last offset     : +0.000000000 seconds
RMS offset      : 0.000000000 seconds
Frequency       : 22.488 ppm slow
Residual freq   : +0.000 ppm
Skew            : 0.000 ppm
Root delay      : 1.000000000 seconds
Root dispersion : 1.000000000 seconds
Update interval : 0.0 seconds
Leap status     : Not synchronised