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: 
You can use the Sysrq trigger in order to make an immediate reset (it's like pressing ALT-BREAK-b):

`echo b >/proc/sysrq-trigger`

BEFORE that, you might want to sync all filesystems, to not lose any data:

`echo s >/proc/sysrq-trigger`

This might only work if CONFIG\_MAGIC\_SYSRQ is enabled in your kernel. The possible keys are explained at [Wikipedia](http://en.wikipedia.org/wiki/Magic_SysRq_key) btw.
Look into a remote KVM switch to reboot without SSH access. 
<http://en.wikipedia.org/wiki/KVM_switch#Remote_KVM_devices>