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I know that it is a "bad" idea, I know that it is not secure, I know. I searched the net for an answer and all I saw was whining that it's not good. But I like using Linux because it lets me make the system I want and like to use. The end of intro.

I try to change password:

ruslan:~% passwd
Changing password for ruslan.
(current) UNIX password:
Enter new UNIX password:
Retype new UNIX password:
You must choose a longer password

If I try sudo passwd ruslan then I can set any password I want so I don't need password complexity checks for passwd on my system.

After googling I've found that there should be PAM module pam_cracklib that tests password for complexity and it can be configured. But my PAM password settings doesn't include pam_cracklib:

% cat /etc/pam.d/passwd | grep '^[^#]'
@include common-password
% cat /etc/pam.d/common-password | grep '^[^#]'
password    [success=1 default=ignore]  pam_unix.so obscure sha512
password    requisite           pam_deny.so
password    required            pam_permit.so
password    optional    pam_gnome_keyring.so 

I guess that pam_unix makes this test... Oops... Guys, the moment I finished to write this sentence I've got an enlightenment and typed man pam_unix in terminal where I've found needed options for pam_unix module.

I just removed option obscure and added minlen=1 and now I'm happy. So now I have this line in /etc/pam.d/common-password:

password    [success=1 default=ignore]  pam_unix.so minlen=1 sha512

and I can set any password I want.

I decided to keep this post for people who might need this solution also. Sorry and thanks.

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AskUbuntu works best if you create and accept the last part as an answer. –  Rinzwind Mar 17 '12 at 11:29
    
I can't answer my own question for 8 hours after asking, will wait :) –  khrf Mar 17 '12 at 11:47
    
I simply wanted to change my pwd to 123. Couldn't do that with passwd. Tried "sudo passwd <user_name>" and it worked like charm. Didn't need rest of the mumbo-jumbo. Thanks for that part! : ) –  zeFree Oct 2 '13 at 13:22
    
@zeFree, the key point of my solution is allowing any user (not having sudo permissions) to use simple passwords –  khrf Oct 4 '13 at 20:29
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2 Answers 2

up vote 11 down vote accepted

Ok, I will answer my question :)

I've found that pam_unix module performs password complexity check and it can be configured.

man pam_unix:

   minlen=n
       Set a minimum password length of n characters. The default value is
       6. The maximum for DES crypt-based passwords is 8 characters.

   obscure
       Enable some extra checks on password strength. These checks are
       based on the "obscure" checks in the original shadow package. The
       behavior is similar to the pam_cracklib module, but for
       non-dictionary-based checks.

so the final line with pam_unix module in my /etc/pam.d/common-password file is:

password    [success=1 default=ignore]  pam_unix.so minlen=1 sha512

It allows me to set any password with minimal length of 1.

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Open common-password config file for editing

sudo gedit /etc/pam.d/common-password

Comment this line :

#password   [success=2 default=ignore]  pam_unix.so obscure use_authtok try_first_pass sha512

Also comment this line, otherwise password setting will ask you to pass a mix of upper/lower case letters :

#password   requisite           pam_passwdqc.so enforce=everyone max=18 min=disabled,8,8,1,1 retry=2 similar=deny

now just add this line into the same file:

password    [success=1 default=ignore]  pam_unix.so **minlen=1** sha512

this should do it...

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