Special characters in password

Question

I am looking for a list of the valid characters which can be used in a user account password on Ubuntu. man passwd just tells me:

As a general guideline, passwords should consist of 6 to 8 characters including one or more characters from each of the following sets:

lower case alphabetics

digits 0 thru 9

punctuation marks

Which is not helping much.

- There have to be some unspoken limits. Tried the same password 5 times and it still didn't work. I reinstalled Ubuntu each time. My full response can be found here: https://askubuntu.com/questions/176337/installed-perfectly-but-password-not-working-for-login-or-authentication/1429239#1429239 — Nicholas Reynolds, Sep 19 '22 at 15:39

score 2 · Answer 1 · edited Jan 24 '14 at 19:58

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Passwords allows the following:

Lowercase Alphabetical (a, b, c, etc.)
Uppercase Alphabetical (A, B, C, etc.)
Numerics (0, 1, 2, etc.)
Special Characters (@, %, !, etc.)

for more details have a look https://help.ubuntu.com/community/StrongPasswords

edited Jan 24 '14 at 19:58

Braiam

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answered Feb 02 '12 at 07:13

One Zero

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This doesn't tell me anything I don't already know.. I want a list of all allowed characters. – wim Feb 02 '12 at 07:32
http://distilledb.com/blog/archives/date/2009/03/06/typing-special-characters-in-ubuntu.page – One Zero Feb 02 '12 at 07:39
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Are you trying to say that ANY special character is allowed ? – wim Feb 02 '12 at 07:54
yes ...in my opinion don't use extra special special character – One Zero Feb 02 '12 at 08:06
Your link in your comment is now broken... You should delete it. – Alexis Wilke Sep 23 '18 at 05:41

David Foerster · Answer 2 · 2018-09-23T08:08:04.463

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User account passwords haven't been stored in Linux since a long time. Instead only password hashes are stored and the hash primitives can all operate on arbitrary (byte) strings. This means that the only limitation on characters in password is the character set of the character encoding used during password entry. By default Ubuntu uses UTF-8, which can encode a superset of all common character sets.

However, you can't enter arbitrary characters (easily) on a common keyboard and you may be restricted to use a different keyboard layout to authenticate with a password than when the password was created.

edited Sep 23 '18 at 08:08

answered Jan 17 '17 at 06:50

David Foerster

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Note that passwords have never been stored as is anywhere, including the `/etc/passwd` file. We only had hashes (way back it was using crypt() which is now considered insecure, but still it was a hash.) Now, though, we save the passwords in a separate file: `/etc/shadow`, which most people do not have access to. – Alexis Wilke Sep 23 '18 at 05:47
@AlexisWilke: Right. That practice started before Linux came into existence. Older Unices did store plain-text passwords though. – David Foerster Sep 23 '18 at 08:06

score 0 · Answer 3 · answered Jan 17 '17 at 04:10

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I suspect some characters are not allowed. I created a password with upper, lower case characters, numbers, and special characters. Wrote it down, tried to login and failed repeatedly. Went to recovery mode, reverted to a simple password and logged in again. I changed the password back to the above complicated one and could not login again. I do not know which of these characters offends the system, but here are the special characters i used. One of them is a problem. # ; . @ [

answered Jan 17 '17 at 04:10

david

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This answer could be improved by making it more specific by testing to find out which special character was not allowed. Some of the special characters in your answer are allowed to be used in passwords. – karel Jan 17 '17 at 05:28

Special characters in password

3 Answers3