TeamCity Maintenance Mode
If on the TeamCity startup you see the TeamCity Maintenance page, that means the TeamCity instance requires technical maintenance which for security reasons is to be performed by a system administrator who has access to the computer where TeamCity server is installed. In most cases this page appears if the data format doesn't correspond to the required format; for example, during upgrade TeamCity will display this page before converting the data to the newer format. If you do not have access to the computer where TeamCity is installed, inform your system administrator that TeamCity requires technical maintenance.
If you are a TeamCity system administrator, to confirm that enter the Maintenance Authentication Token into the corresponding field on this page. This token can be found in the teamcity-server.log file under TeamCity Server Logs.
After you have provided this token, you can review the details on what kind of maintenance is required. The need in technical maintenance may be caused, for example, by one of the following:
TeamCity Data Upgrade
When upgrading your TeamCity instance, the newly installed version of TeamCity checks if the TeamCity data directory and database use the old data format when it is started for the first time. If the newer version requires data conversion, this page is displayed with data format details. Please, review them carefully.
If you haven't backed your data up, do it at this point. Once TeamCity converts the data, downgrade won't be possible. If you need to return to earlier TeamCity version, you will be able to do so only by restoring the data from corresponding backup. Please refer to the TeamCity Data Backup section for instructions. When you are sure you have your data backed up, click Upgrade.
TeamCity Data Format is Newer
TeamCity has detected that the data format corresponds to more recent TeamCity version than you try to run. Since downgrade is not supported, TeamCity cannot start until you provide the data that matches the format of the TeamCity version you want to run. To do so, please restore the required data from backup. Refer to the Restoring TeamCity Data from Backup page for the instructions.
TeamCity Startup Error
If on TeamCity startup a critical error was encountered, this page will display the error message. Please, fix the error cause and restart the TeamCity server.