Ubuntu 20.04
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Set Password Rules2020/09/07
 
Set Password Rules with [pam_pwquality] module.
[1] Install password quality checking library.
root@dlp:~#
apt -y install libpam-pwquality
[2] Set number of days for password Expiration.
Users must change their password within the days.
This setting impacts only when creating a user, not impacts to exisiting users.
If set to exisiting users, run the command [chage -M (days) (user)].
root@dlp:~#
vi /etc/login.defs
# line 160: set password Expiration days (example below means 60 days)

PASS_MAX_DAYS
60
[3] Set minimum number of days available of password.
Users must use their password at least this days after changing it.
This setting impacts only when creating a user, not impacts to exisiting users.
If set to exisiting users, run the command [chage -m (days) (user)].
root@dlp:~#
vi /etc/login.defs
# line 161: minimum number of days available (example below means 1 day)

PASS_MIN_DAYS
1
[4] Set number of days for warnings before expiration.
This setting impacts only when creating a user, not impacts to exisiting users.
If set to exisiting users, run the command [chage -W (days) (user)].
root@dlp:~#
vi /etc/login.defs
# line 162: set number of days for warnings (example below means 7 day)

PASS_WARN_AGE
7
[5] Limit using a password that was used in past.
Users can not set the same password within the generation.
root@dlp:~#
vi /etc/pam.d/common-password
# line 26: add [remember=*] (example below means 5 gen)

password        [success=1 default=ignore]      pam_unix.so obscure use_authtok try_first_pass sha512 remember=5
[6] Set minimum password length.
Users can not set thier password length less than this parameter.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 11: uncomment and set minimum length (example below means 8 char)

minlen =
8
[7] Set minimum number of required classes of characters for the new password.
(kinds ⇒ UpperCase / LowerCase / Digits / Others)
root@dlp:~#
vi /etc/security/pwquality.conf
# line 34: uncomment and set parameter (example below means 2 kinds)

minclass =
2
[8] Set maximum number of allowed consecutive same characters in the new password.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 38: uncomment and set parameter (example below means 2 char)

maxrepeat =
2
[9] Set maximum number of allowed consecutive characters of the same class in the new password.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 43: uncomment and set parameter (example below means 4 kinds)

maxclassrepeat =
4
[10] Require at least one lowercase character in the new password.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 25: uncomment and set parameter (example below means 1 char)

lcredit =
-1
[11] Require at least one uppercase character in the new password.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 20: uncomment and set parameter (example below means 1 char)

ucredit =
-1
[12] Require at least one digit in the new password.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 15: uncomment and set parameter (example below means 1 char)

dcredit =
-1
[13] Require at least one other character in the new password.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 30: uncomment and set parameter (example below means 1 char)

ocredit =
-1
[14] Set maximum length of monotonic character sequences in the new password.
(ex ⇒ '12345', 'fedcb')
root@dlp:~#
vi /etc/security/pwquality.conf
# add to the end (example below means 2 characters are allowed but more than 3 characters are not allowed)

maxsequence = 2
[15] Set number of characters in the new password that must not be present in the old password.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 6: uncomment and set parameter (example below means 5 char)

difok =
5
[16] Check whether the words longer than 3 characters from the GECOS field of the user's passwd entry are contained in the new password.
root@dlp:~#
vi /etc/security/pwquality.conf
# line 47: uncomment and change to enabled

gecoscheck =
1
[17] Set space separated list of words that must not be contained in the password.
root@dlp:~#
vi /etc/security/pwquality.conf
# add to the end

badwords = denywords1 denywords2 denywords3
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