Slackware alatt:
man useradd
...
Usernames must start with a lower case letter or an underscore, followed by lower case letters, digits, underscores, or dashes. They can end with a dollar sign. In regular expression terms:
[a-z_][a-z0-9_-]*[$]?
...
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A főnököm mindig megtartja amit ígér, ha pénzt ígér azt is!