I am trying to set up a small desktop machine that plays nicely with some Red Hat servers, and would like my username on the local machine to match my username on the servers. My username on these servers is in the format first.last, and neither ubuntu nor debian allow you to create a username with a dot in the graphical interface. I could useradd first.last just fine, but then on reboot the login screen on gdm prevented me from logging in as any of the users.
What is going on here? Can I really not have a dot in my username? Is there a workaround? This seems quite odd. from what I've read, this used to be a problem 10 years ago because useradd did not yet have support, but I haven't seen any posts more recent than 2004 that discuss this issue.