Why are dots in username & groupname no longer allowed?

[redhat at barendse.to (Remco Barendse)]

On Fri, 6 Jan 2006, Adam Gibson wrote:

> Josh Kelley wrote:
>> On 1/5/06, Johnny Hughes <mailing-lists@xxxxxxxxxxxx> wrote:
>>> BUT, the I think that the real reason that dots should not be allowed in
>>> user names is because this doesn't allow dots:
>>> 
>>> RFC 4282 - The Network Access Identifier
>>> 
>>> There is no requirement to follow this for usernames; however, I think
>>> we should.
>> 
>> Unless I'm misreading the RFC, it does allow dots in usernames?
>> 
>>    nai         =  username
>>    nai         =/ "@" realm
>>    nai         =/ username "@" realm
>> 
>>    username    =  dot-string
>>    dot-string  =  string
>>    dot-string  =/ dot-string "." string
>
> I don't know myself but Fedora Core 4 allows dots in usernames.  useradd 
> asdf.adsf under Fedora Core 4 works just fine as well as userdel asdf.asdf . 
> I wonder which direction RHEL will follow in the future since Fedora is 
> usually the test ground for newer stuff in RHEL.

It seems it's really a bug in RHEL 3, RHEL 2.1 allows a dot, so does RHEL 
4.x (and IMHO a dot should be allowed, I don't care if a package from the 
previous millennium doesn't work anymore)

I wonder if I could just install shadow-utils from RHEL4 on my CentOS 3.x 
boxes (maybe it will work after rebuilding the RPM)