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NTP server

The university time server. Synchronise your clock against a source inside the TUKE network instead of public servers abroad. Available from the internet as well.

ntp.tuke.sk

  • Stratum 1

    The server is synchronised directly from GPS, not via another NTP server.

  • Low latency

    Round-trip time inside the university network is a few milliseconds.

  • Publicly available

    Works from the university network and from the internet, no registration.

  • Servers and workstations

    Suitable for virtual servers, workstations and network equipment.

Server parameters

Parameter Value
Address ntp.tuke.sk
IP address 147.232.3.100
Port 123/UDP
Stratum 1
Reference clock GPS
Protocol versions NTPv3 and NTPv4
Server precision approximately 4 µs
IPv6 Not available
NTS Not available
Availability Public, from the TUKE network and the internet

What stratum 1 means

Stratum indicates the distance from the reference clock. Stratum 1 is a server attached directly to a time source, here GPS. Common public pool servers are stratum 2 or 3, that is one or two steps further away.

Why use the university server

A shorter path

Traffic does not travel abroad. A shorter, more stable route means more accurate synchronisation.

A known source

You know who runs the server and where the time comes from.

Works without internet

Devices inside the university network can synchronise even when they have no outside access. It works from home just as well, the server is public.

Configuration on Ubuntu

Ubuntu ships with systemd-timesyncd by default. If you need more accurate synchronisation or several sources, use chrony.

Edit the configuration

sudo nano /etc/systemd/timesyncd.conf

Set:

[Time]
NTP=ntp.tuke.sk
FallbackNTP=ntp.ubuntu.com

Restart timesyncd

sudo systemctl restart systemd-timesyncd
sudo timedatectl set-ntp true

Check the timesyncd status

timedatectl timesync-status

The output should show Server: 147.232.3.100 (ntp.tuke.sk) and a non-zero Offset.

Install chrony

sudo apt update && sudo apt install -y chrony

Set the time source

sudo nano /etc/chrony/chrony.conf

Comment out the pool lines and add:

server ntp.tuke.sk iburst
driftfile /var/lib/chrony/chrony.drift
makestep 1.0 3
rtcsync

What those options do

iburst speeds up the first synchronisation after start. makestep 1.0 3 allows a step correction during the first three measurements if the offset exceeds one second.

Restart chrony

sudo systemctl restart chrony
sudo systemctl enable chrony

Check the chrony status

chronyc sources -v
chronyc tracking

In chronyc sources the server should carry an asterisk ^*, meaning the clock is being steered by it.

Without changing the configuration and without touching the system clock:

sudo chronyd -Q "server ntp.tuke.sk iburst"

The output shows how far off your clock is:

System clock wrong by -0.001626 seconds (ignored)

Configuration on Windows

In a command prompt started as administrator:

w32tm /config /manualpeerlist:"ntp.tuke.sk,0x8" /syncfromflags:manual /update
net stop w32time && net start w32time
w32tm /resync

Verification:

w32tm /query /status
w32tm /query /source

Domain-joined machines

A workstation joined to a domain takes its time from the domain controller and a manual setting is overwritten. Make the change on the controller instead.

Verifying synchronisation

A quick check that the system synchronises time at all:

timedatectl

Look for:

Line Expected value
System clock synchronized yes
NTP service active

Details about the source and offset:

chronyc tracking              # when using chrony
timedatectl timesync-status   # when using systemd-timesyncd

Troubleshooting

System clock synchronized: no

The service is not running or has no time source.

systemctl status chrony systemd-timesyncd
sudo timedatectl set-ntp true

Only one of them can run at a time. When you install chrony, Ubuntu disables systemd-timesyncd automatically.

Server unreachable or no reply

NTP uses UDP port 123. Check the firewall:

sudo ufw allow out 123/udp

Outbound UDP 123 is often blocked in containers and on some networks.

Time does not synchronise in a virtual machine

Virtual machines often take their time from the hypervisor. On VMware this is handled by VMware Tools, so an NTP client usually is not needed at all. If you configure one anyway, the two sources may conflict.

A large offset is not corrected

By default the clock is slewed gradually. Force a step correction with chrony's makestep, or manually:

sudo chronyc makestep

Frequently asked questions

Do I have to request access?

No. The server is publicly available, works from the university network and from the internet, and requires no registration.

Does the server support IPv6 or NTS?

No. IPv4 and plain unencrypted NTP are available. We verified that the domain has no AAAA record and that port 4460 for NTS is closed.

Should I add a fallback server?

On workstations it is sensible to keep the public pool as FallbackNTP. On servers inside the university network ntp.tuke.sk alone is usually enough.

How accurate is the server?

It reports a precision of roughly 4 µs and a root dispersion below 0.2 ms. The practical accuracy of your own machine will be an order of magnitude worse, limited by network latency.

Next steps

  • Ubuntu

    First steps after creating a virtual server.

    More info

  • All services

    An overview of TUKE cloud services.

    Open