You can force Mango to start up in Safe Mode by creating an empty file named "SAFE" (no quotations) with no file extension in the root Mango installation directory. In a Linux/Windows/Mac environment, this is the directory the operator chose to install Mango in. In a MangoES unit, the directory is /opt/mango/
The SAFE file can be added via the Webmin File Manager with the "Create File" button or via the terminal using the "touch" command.
The Data Sources will be disabled in the database. If possible you might want to export the JSON of your data sources prior to this or use a previous Data Source export to import to re-enable the Data Source. This is helpful if you have some Data Sources disabled and it's hard to remember which ones.