Question: I know that Linux may, depending on configuration, allow the interactive user to reboot the server by pressing `Ctrl`-`Alt`-`Del` even without logging in. I have a **remote console** session over SSH to a remote server that I cannot log into, but I want to reboot it. Is it possible to somehow send the key combination `Control`-`Alt`-`Delete` over SSH (or `telnet`)? If so, how?

**Edit:** to clarify, I am not just connected to the server's `sshd` over `ssh` - I am connected via a KVM over IP switch, so it's a serial console. But this connection itself is over SSH and my question is how to send the `Ctrl`-`Alt`-`Del` key combination over it.

Answer: 
In a comment you mention (ttyS0) - this isn't the local console, it's a serial console.

I don't think you can do Ctrl-Alt-Del from the serial console.

<http://osdir.com/ml/linux.hardware.dell.poweredge/2003-01/msg00200.html> suggests a way getting magic-sysrq working over serial - maybe this would be sufficient for rebooting a server?
Is it possible the command has been disabled? I regularly disable it on my production servers, usually to protect them from me when I forget that I'm logging into a Linux machine instead of a Windows machine and accidentally press Ctrl-Alt-Del and subsequently reboot the machine.

On machines which I do leave it so that a non-technical person can reboot, I extend the time in Dan's example from "now" to "2 minutes" so there's a sliver of a chance the reboot can be aborted if needed.