Started Build Agent is not available on the server to run builds

First start of agent after installation or TeamCity server upgrade/plugin installation can take time as agent downloads updates form the server and auto-upgrades.
Regularly, agent should become connected in 1 to 10 minutes, depending on the agent/server network connection speed.

If the agent is not connected within that time, check the name of the agent (as configured in conf\buildAgent.properties file) and check the tabs under the Agents server UI section:

• the agent is under Connected - the agent is ready to run builds
• the agent is under Disconnected - the agent was connected to the server, but became disconnected. Check the "Inactivity reason" in the table. If the reason is "Agent has unregistered (will upgrade)", then wait for several more minutes
• the agent is under Unauthorized - all the agents connected to the server for the first time should be authorized by a server administrator

If the agent stays in the state for more than 10 minutes and you have a fast network connection between the agent and the server, please:

• check the agent process is running and the serverURL in conf\buildAgent.properties is correct;
• check that all the requirements are met;
• check agent logs (teamcity-agent.log, launcher.log, upgrade.log) for any related messages/errors;
• check server logs (teamcity-server.log) for any messages/errors mentioning agent name or IP.

If you cannot find the cause of the delayed agent upgrade in the logs, contact us and provide the full agent and server logs. Please also check/include the state of the agent processes (java ones) on the agent machine.