username best practices and other conventions

[Miloslav Trmac]

Hello,
Dax Kelson napsal(a):
> Since, well forever, I've understood the UNIX and Linux username best
> practices to be:
I don't know about best practices, but FWIW these are the hard limits in
shadow-utils and libuser:

> (a) all lowercase
> (b) alphanumeric with exception that first char must not be a number
[a-zA-Z0-9.-_]*, first char must not be -.  First char can be a number,
in fact the user name can be completely numeric (which of course a
stupid thing to do).
> (c) 8 char max length
UT_NAMESIZE - 1 (31) bytes.

> The origin of (a) I believe comes from the fact that historically there
> was a one-to-one mapping between email addresses and usernames and since
> email addresses are not case sensitive, usernames that only differ by
> case cause email ambiguities.
One other possible reason is that traditional UNIX supported
uppercase-only terminals (by mapping all characters to uppercase on
output and to lowercase on input), and getty would switch to the
uppercase-only mode when the username was entered in all uppercase.  I
have seen this behavior on Debian about five years ago.
	Mirek