TeamCity agent "unauthorized" / not authorized on the server in CI

A newly connected or re-registered agent appears under Unauthorized agents. TeamCity does not send builds to an unauthorized agent, so it stays idle until an administrator authorizes it.

What this error means

The agent connects but never runs builds; Administration, Agents shows it under "Unauthorized" with a status like "Agent has been unauthorized: ...".

TeamCity

Agent "Agent-1" is not authorized.
Status: Agent has been unauthorized: New agent auto-authorization is disabled.

Common causes

A new agent awaiting authorization

By default, a freshly registered agent is unauthorized until an administrator approves it, which limits which hosts can run builds.

The agent was manually or automatically unauthorized

An administrator revoked authorization, or an automatic policy unauthorized it (for example, after a token or name change).

How to fix it

Authorize the agent

Open Administration, Agents, Unauthorized.
Select the agent and click Authorize, confirming it belongs to a trusted host.
Assign it to the correct agent pool so eligible builds can use it.

Verify the agent identity before authorizing

Confirm the name and authorizationToken in buildAgent.properties match the intended host so you do not authorize an unexpected machine.

buildAgent.properties

# <agent>/conf/buildAgent.properties
name=Agent-1
authorizationToken=<token>

How to prevent it

Decide an explicit authorization policy for new agents.
Keep agent names and tokens stable so re-registration does not deauthorize them.
Document which hosts are trusted to run builds for each pool.