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Both the main TeamCity server and build messages processor can be started / stopped using regular TeamCity scripts (teamcity-server.bat, teamcity-server.sh) or Windows services.
The build messages processor uses the same approach to logging as the main server. You can check how the startup is doing in the <TeamCity installation directory>/logs/teamcity-server.log file. You can also open <processor URL> in your browser, there you should see regular TeamCity startup screens.
Enabling Build Messages Processor
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