Sorry about the short notice. I went to install a package update, and saw that a new Ubuntu upgrade was available. I punched that button without thinking too hard about the consequences, and now the server is in the middle of an OS upgrade which will take I-don't-know-how-long.
It might be back tonight, but then I may not have time to bring everything back up tonight. To be (belatedly) safe, I'll say it will be back tomorrow afternoon. If it's sooner than that, I'll post here.
EDIT-ADD: Okay, I got everything back up at 7:45 pm Eastern. I think it's all okay now. Please report any unexpected problems.