user name does not exist

[Ummon]

I was installing Vbox when I got to this command:

usermod -a -G vboxusers user_name

which for some reason gives me the error:

usermod: user 'user_name' does not exist. It does not matter what I put in place of user_name. Also, when I uninstalled and reinstalled I could no longer create 64-bit virtual machines. I tried searching the forums for answers, but it didn't seem to deal with my specific problem in fedora 24. Any help would be appreciated.

[mpack]

Try replacing the place holder "user_name" with your user name.

If you can't get "usermod" to work then that would be a question for a Fedora forum.