Does character 'ä' in usernames cause bugs in linux systems?

Question

I want to use my first name as an username but it contains character 'ä'. I found this thread.

Now I understand, why some some characters are disabled, but what about 'ä'? Can this character cause any problems?

Why are some unicode characters (ü, õ, ö, ä) disabled, when they are used in full names?

Answer 1

On a modern system (with full-out Unicode support), this shouldn't be a problem - with emphasis on "shouldn't". As quoted in that answer,

The default is NAME_REGEX="^[a-z][-a-z0-9]*\$"

Although this may be overly strict for current systems, it makes for easier administration - as in, "one less thing to worry about". Note that the username gets used in many places - e.g. your home directory would probably be of the form /home/username; most sane filesystems have full Unicode support, but as with anything computer-related, sanity under all circumstances is not guaranteed.

Note that there is the actual login name as used by the system (which falls under these rules), mapped to an UID in /etc/passwd, and there's "Full Name", which is a string (and most valid characters can be entered, although there's a "non-ASCII" warning).

What to do: Where applicable, I use the name without diacritics (or romanized, in case of non-Latin scripts) for username, and the real form for Full Name. The entry in your /etc/passwd might then look similar to this:

martrang:x:1001:1001:Märt Rang,,,:/home/martrang:/bin/bash

Answer 2

The last question is the easiest to answer: Tradition, practicality, simplicity (for the developer) and portability, if you want to be charitable, or alternatively backwardness, impracticality (for the user), ignorance and non-portability, if you don't. US-ASCII is simply the character set which has been used since the dawn of time (pre-web for the youngsters) pretty much everywhere.

In many, many applications there are simply no built-in support for characters outside of what you can see on an English keyboard (and sometimes not even that). In other words, the software may or may not support it, and you can only expect the unexpected.

Answer 3

Using non-ASCII login names is not generally supported and sounds like a recipe for trouble. While UTF-8 is becoming the de facto standard encoding, there are still many people who use other encodings (especially outside the English-speaking world, where people have been using other, incompatible 8-bit or 16-bit encodings for a long time). For example, you're likely to encounter applications that try to interpret your username according to the current locale's encoding, rather than (attempt to) translate it to the current locale's encoding. Your login name is also the left-hand part of your email address, and that is even more likely to cause problems since you're depending on your chosen encoding being supported and respected by all the systems that your mail goes through.

The login name is intended for computers. Use ASCII in your login name. The full name is intended for humans. Use UTF-8 in your full name.