Go to Control Panel -> Server Administration -> Shutdown
Fill the messages, and click on Shutdown.
A message appears on the top of the screen, and a Cancel Shutdown button next to Shutdown button.
The Shutdown button should disappear, because no any sense. You can use Cancel Shutdown.
6.2.x git id: 8b37e24c5c6e8e1f072a47ac9e2a54ab0d90baa4