It just returns an empty line 
core-ssh:~# echo $HASSIO_TOKEN
core-ssh:~#
When I had that variable missing it wasn’t working, I configured it and it worked immediately . To fix I copied the HASSIO_TOKEN from the correctly working shell, which in my case was zsh vs bash so it was easy to obtain - simply log into the zsh shell and run the previous command:
echo $HASSIO_TOKEN
to set on missing shell save the output of that command into your shell startup params (.bash_profile, .bashrc etc.)
Little update on this: I just figured out the following on my Hassio System-Logfile (Webfrontend -> Hassio -> System):
18-10-13 14:41:48 WARNING (MainThread) [hassio.api.security] No API token provided for /host/shutdown
It seems that ryanb33 pointed out the actual problem. I’m going to give his solution a try in the next days. But how do i use another shell? Sorry, i’m a little unix-noob 
@blackmesa Did you get this figured out? I am experiencing this same issue and am unsure how to proceed.
Thanks!
Hey folks,
I never solved this problem with the missing API token. Because just a few days after my last posting my file system on the sd card got broken (https://community.home-assistant.io/t/my-hassio-crashed-over-night-file-system-seems-to-be-read-only/73374. Due to that error i got to set up my hassio-system again. This time I used the new version based on HassOS instead of ResinOs. I works perfectly with none of the issues I experienced before 
That’s what I ended up ding as well oh well the newer versions are very slick!
This power outage and getting HASSIO totally broken happened to me several times now. I had to flash a new IMG on the SD card and restore from backup
Yes, this happened to me several times. I suspect Docker to be the root cause. You need an UPS for running Docker based systems. At least this is what some suggest in the WWW. Docker is made for data centers, not for devices that can have power outages without proper shutdown.