What chars can REALLY be in usernames?

[P E Smee]

We're now (at the whim of our management) engaged in the problem of
trying to find a form of username which will work on all of our
machines, so that (modulo case, which we can cope with) any given
person will have the same username on all the boxes he is registered
on.  This is a bit tricky as we have various Unix boxes, VAX/VMS, and
IBM VM/CMS to cater for.

As I said, we can make all the systems appear case-insensitive at the
user level, so it's ok that I might be named PAUL on CMS and paul on
Unix -- could still type 'paul' to get in.  Problem is, we have found
an FM which says that Unix names must be lowercase ALPHA only.  None of
us has, however, ever seen a Unix system which actually forces such a
strict limit.

So, the real, precise, question, is: has anyone out there ever seen a
real, commercially available modern Unix implementation which will
object to either or both of digits and underline characters in its
usernames?  And, if so, whose, and what chars does it allow?

-- 
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