Rules for User name:
- First character of a username must be a lower-case letter, or the underscore '_' character.
- Subsequent characters of a username may be lower-case letters, underscore, or dash '-' character.
- The very last character of a username is permitted to be a dollar sign '$'
- Maximum total length is 32 characters
Put another way (straight from the code of 'useradd' linux utility):
- User/group names must match [a-z_][a-z0-9_-]*[$]
Description can be any text, maximum length is 64 characters.
Password can be any combination of upper/lower case letters, digits, and punctuation. Maximum length is set to 40 characters.
If you're getting a "failed to add entry for user" error, check the description. Make sure there are no odd characters such as quotes or colon.