Couldn't get a file descriptor referring to the console error

Hi:
When I tried to replace the command run by the instructor in Response Time Degradation, Part 3:
$ open rtd.html
Couldn’t get a file descriptor referring to the console
Why does this error occur?
Thanks,
RT

What is your os?
What was the original command which was changed
open is for Macos
Try xdg-open on Ubuntu