On a Debian Linux machine I had the problem, that a reboot was no longer possible. Some time after issuing the “reboot” command, I got the message:
Failed to set wall message, ignoring: Transport endpoint is not connected
Call to Reboot failed: Transport endpoint is not connected
In this case I was able to force a reboot of the machine by issuing the following command:
echo b | sudo tee /proc/sysrq-trigger
Just as a reminder, if I need that again in future 😉
Debian Linux: Force Reboot