Time Synchronization (chrony)

Accurate system time is critical for logging, certificate validation, distributed system coordination, and more. Enterprise Linux distributions use chrony as the default NTP client and server, replacing the legacy ntpd. This guide covers chrony installation, NTP source management, timezone configuration, and hardware clock synchronization.

chrony vs ntpd

Feature	chrony	ntpd
Sync speed	Fast convergence, works with intermittent connections	Slower convergence, needs persistent connection
Resource usage	Low memory and CPU	Relatively higher
VM support	Excellent, handles clock drift well	Average
EL default	Default since EL 7	Default in EL 6, removed in EL 8+
Accuracy	Microsecond level	Millisecond level

In EL 8/9, ntpd has been removed from the default repositories. chrony is the only recommended NTP implementation.

Installing chrony

chrony is typically pre-installed on EL distributions. If not, install it manually:

sudo dnf install chrony -y

sudo systemctl start chronyd
sudo systemctl enable chronyd

sudo systemctl status chronyd

Checking Synchronization Status

chronyc sources — View NTP Sources

chronyc sources -v

Column indicators explained:

^* — Currently synced source (active)
^+ — Acceptable alternative source
^- — Not considered for synchronization
^? — Connecting or unknown state

chronyc tracking — View Sync Details

chronyc tracking

Key fields to watch:

System time — Offset between system clock and NTP
Last offset — Offset of the last adjustment
RMS offset — Root mean square of offsets
Frequency — Clock frequency deviation (ppm)

chronyc sourcestats — View Source Statistics

chronyc sourcestats -v

Configuring NTP Servers

The main configuration file is /etc/chrony.conf.

View the Default Configuration

cat /etc/chrony.conf

Change NTP Servers

The default configuration usually points to the distribution’s NTP pool. You can modify it as needed:

sudo cp /etc/chrony.conf /etc/chrony.conf.bak

sudo vi /etc/chrony.conf

Example NTP server configuration:

# Use global NTP pool servers
pool 2.pool.ntp.org iburst
server time.cloudflare.com iburst
server time.google.com iburst

# Record the rate at which the system clock drifts
driftfile /var/lib/chrony/drift

# Allow the system clock to be stepped in the first three updates
makestep 1.0 3

# Enable kernel synchronization of the real-time clock
rtcsync

# Log directory
logdir /var/log/chrony

Key directive explanations:

server — Specify a single NTP server
pool — Specify an NTP server pool (auto-resolves multiple addresses)
iburst — Send burst requests during initial sync for faster convergence
makestep — Allow large time adjustments under specified conditions (params: threshold in seconds + max number of adjustments)
rtcsync — Write system time to hardware clock every 11 minutes

sudo systemctl restart chronyd

chronyc sources

Configure as an NTP Server

To serve time to other hosts on your local network:

echo 'allow 192.168.1.0/24' | sudo tee -a /etc/chrony.conf

sudo systemctl restart chronyd
sudo firewall-cmd --permanent --add-service=ntp
sudo firewall-cmd --reload

Timezone Management (timedatectl)

timedatectl is the systemd utility for managing time and timezone settings.

View Current Time Information

timedatectl status

List Available Timezones

timedatectl list-timezones

timedatectl list-timezones | grep America

Set the Timezone

sudo timedatectl set-timezone America/New_York

sudo timedatectl set-timezone UTC

Enable / Disable NTP Synchronization

sudo timedatectl set-ntp true

sudo timedatectl set-ntp false

Manually Set the Time

After disabling NTP synchronization, you can manually set the system time:

sudo timedatectl set-time '2026-03-25 14:30:00'

Hardware Clock Synchronization

The hardware clock (RTC) is an independent clock on the motherboard that keeps running when the system is powered off.

View the Hardware Clock

sudo hwclock --show

Sync System Clock to Hardware Clock

sudo hwclock --systohc

Sync Hardware Clock to System Clock

sudo hwclock --hctosys

Set Hardware Clock to UTC

sudo hwclock --systohc --utc

With the rtcsync directive enabled, chrony automatically syncs the system time to the hardware clock every 11 minutes, so manual intervention is rarely needed.

Force Immediate Synchronization

If the system time has drifted significantly and needs immediate correction:

sudo chronyc makestep

This command instantly adjusts the system time to match the NTP source, regardless of the offset.

Common Troubleshooting

Unable to Synchronize Time

systemctl is-active chronyd

sudo firewall-cmd --list-services | grep ntp

chronyc activity

View chrony Logs

journalctl -u chronyd --no-pager -n 50

Check Time Offset

chronyc tracking | grep "System time"

The offset should be at the millisecond or microsecond level. If the offset is too large (more than a few seconds), use chronyc makestep to force synchronization.

Best Practices

Keep chrony as the default time service — Do not install ntpd on EL 8/9
Use geographically close NTP sources — Reduces latency and improves accuracy
Configure multiple NTP sources — At least 3-4 sources for redundancy
Use the iburst option — Speeds up initial synchronization
Keep the makestep configuration — Allows large time adjustments at startup
Enable rtcsync — Keeps the hardware clock synchronized
Monitor time offset — Include chronyc tracking in your monitoring system