"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_-]*[$]?"
It is usually recommended to only use usernames that begin with a lower case letter or an underscore, followed by lower case letters, digits, underscores, or
dashes. They can end with a dollar sign. In regular expression terms: [a-z_][a-z0-9_-]*[$]?
On Debian, the only constraints are that usernames must neither start with a dash ('-') nor plus ('+') nor tilde ('~') nor contain a colon (':'), a comma (','),
or a whitespace (space: ' ', end of line: '\n', tabulation: '\t', etc.). Note that using a slash ('/') may break the default algorithm for the definition of the
user's home directory.(Not much point in continuing this, since the post has dropped from front page to 7th in half an hour, and will never be seen again.)
* http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_...
* http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_...
Valid portable user names can have digits and letters intermixed. They are simply restricted to not starting with a minus.
* https://github.com/systemd/systemd/issues/6237 (https://news.ycombinator.com/item?id=14681377)
In the actual bug report, as opposed to Mattias Geniar's article headlined here, this is already mentioned.
What happens when admin typos a username in this fashion? The system they think is conforming to least privilege suddenly is granting most privilege. Thanks systemd!
It's like the code is as self-righteous as its author.