GitHub Actions "The runner is using an unsupported OS"

The self-hosted host runs an OS version the runner agent no longer supports (for example an end-of-life Linux release), so GitHub blocks it from running jobs.

What this error means

The runner logs "##[error]The runner is using an unsupported OS" and fails to register or stops acquiring jobs.

github-actions

##[error]The runner is using an unsupported operating system. Update the host OS to a supported version.

Common causes

End-of-life host OS

The host runs a distro release past its support window, which the current runner agent refuses to run on.

Missing OS dependencies

The OS lacks libraries (glibc, libicu) the runner needs, which presents as an unsupported-OS failure.

How to fix it

Move to a supported base

Check the runner release notes for the supported OS matrix.
Upgrade the host (or container base image) to a supported release.
Install required dependencies the agent needs.
Re-register the runner and confirm it reaches Idle.

Use maintained managed images

Managed runners are kept on supported, GitHub-parity OS images so you never hit an unsupported-OS block on your own hosts.

How to prevent it

Track host OS against the runner support matrix.
Rebuild runner images before the base OS goes end-of-life.
Keep required runtime libraries installed.