What is the logic behind the user name restrictions in *buntu?

In Fedora, I use my preferred account name, which happens to be a fully qualified domain name. By using a fully qualified domain name as my user name across most of my accounts (both on my own computer and across the web), I minimize the chance that my usual user name is taken.

There are some services that do not allow this, due to character restrictions, and that is fine. But in Fedora, my usual name works. This is proof that GNU/Linux CAN handle user names that begin with a digit (as mine does) and contain dots. However, *buntu does not allow this, and I have to use a permutation of my name. Ignoring the outright disallowing of dots, *buntu even does fine with digits, but not at the beginning ... Strange.

Is this a problem? No, not really. I'm not looking for a solution. I just want to know WHY this is. Is this purely arbitrary, or is there some reason for these odd restrictions? Why is *buntu unable to offer as much flexibility in this area?

Solution 1:

Just to test you could use sudo adduser --force-badname '<whatever-name-you-want>' and add it the relevant groups needed by you (eg. sudo, netdev, sambashare etc)

Log in, look around, see if nothing breaks. If everything is fine then you could even keep using that username.