# Configure time servers


> Screens use NTP to keep their clocks accurate. Allow ntp.ubuntu.com, or point players at a time server on your own network.
A player keeps its clock through Network Time Protocol, and an accurate clock is a requirement rather than a nicety. Security depends on it, and so does playback: a screen with the wrong time runs your schedule at the wrong time.

By default players use `ntp.ubuntu.com`.

## On a corporate network

Either allow `ntp.ubuntu.com` through the firewall on port 123, or point players at a time server you already run.

## Adding your own servers

Time servers are set through the [Network Config Generator](/os/network-config-generator/), the same tool used for Wi-Fi and static addressing.

1. Open the [Network Config Generator](/os/network-config-generator/).
2. Turn on **Configure NTP settings**.
3. Enter your time server, and use the add button to list more than one.
4. Generate the file and apply the `network.yaml` from a USB drive, as in [Connect to Wi-Fi](/docs/screenlyos/networking/guides/connect-to-wifi/).

[ntppool.org](https://www.ntppool.org) is a source of public servers if you do not run your own.

Listing more than one is worth doing wherever the primary server is not guaranteed. A player that cannot set its clock reports an error rather than quietly carrying on, so a single unreachable server takes the screen out of service.

## If you see a time server error

See [Diagnostic errors](/docs/screenlyos/networking/reference/diagnostics-errors/) for what to check.