If you’re running a magento site and you might randomly run into your website throwing this error:
Service Temporarily Unavailable The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.
If you do, do not panic. When Magento is performing certain tasks it temporarily creates this file. Magento checks for its existence and if it’s there will send users to the page you described. By default, it is supposed to automatically delete the file after the task is complete. However, for some reason, it doesn’t get deleted all the time.
In Order to fix this, you’ll need to access the root folder of your Magento installation and look for this file : maintenance.flag. If you do find one, you can delete it.
In Magento 2 and higher versions, the maintenance.flag file is located in the /var folder of your Magento installation. The steps remain the same though. Access the folder and delete the file.
On a side note, if you would like to enable maintenence mode for your installation. You can follow One of these steps: