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