Last night as I was upgrading my new server, I ran the command

shutdown -h 00:10. Before the shutdown could complete, something interrupted my ssh session. As a result, when I tried to log back in, I received the following message:

The system is going down on Thu Jun 2 00:10:36 2011

and was immediately disconnect.

The problem was, it was already half an hour after the time in the message, and I had rebooted the server already.

After some research into the shutdown command, I discovered that there is a file created in /etc/ that is created upon issuing the shutdown command. This file, named nologin prevents normal users from logging in as long as it exists.

In order to allow my regular user to log on again, I had to log in as root, and then delete the file with:

rm /etc/nologin

As soon as this file was gone, my server once again allowed me to log in as before.