我们在使用linux系统设置密码的时间 ，经常遇到这样的问题 ，系统提醒：您的密码太简朴 ，或者您的密码是字典的一部门 。那么系统是怎样实现对用户的密码的庞大度的检查的呢 ？
声明：login.defs主要是控制密码的有用期 。对密码举行时间治理 。此处不细谈
login.defs --shadow password suite configuration
可以rpm -ql cracklib检察
密码的庞大度的判断是通过pam模块控制来实现的 ，详细的模块是pam_cracklibpam_cracklib 的参数先容：
This option makes the module write information to syslog(3) indicating the behavior of the module (this option does not write password information to the log file).
The default action is for the module to use the following prompts when requesting passwords: "New UNIX password: " and "Retype UNIX password: ". The default word UNIX can be replaced with this option.
Prompt user at most N times before returning with error. The default is 1
This argument will change the default of 5 for the number of characters in the new password that must not be present in the old password. In addition, if 1/2 of the characters in the new password are different then the new password will be accepted anyway.
How many characters should the password have before difok will be ignored. The default is 23.
The minimum acceptable size for the new password (plus one if credits are not disabled which is the default). In addition to the number of characters in the new password, credit (of +1 in length) is given for each different kind of character (other, upper, lower and digit). The default for this parameter is 9 which is good for a old style UNIX password all of the same type of character but may be too low to exploit the added security of a md5 system. Note that there is a pair of length limits in Cracklib itself, a "way too short" limit of 4 which is hard coded in and a defined limit (6) that will be checked without reference to minlen. If you want to allow passwords as short as 5 characters you should not use this module.
(N >= 0) This is the maximum credit for having digits in the new password. If you have less than or N digits, each digit will count +1 towards meeting the current minlen value. The default for dcredit is 1 which is the recommended value for minlen less than 10.
(N < 0) This is the minimum number of digits that must be met for a new password.
(N >= 0) This is the maximum credit for having upper case letters in the new password. If you have less than or N upper case letters each letter will count +1 towards meeting the current minlen value. The default for ucredit is 1 which is the recommended value for minlen less than 10.
(N > 0) This is the minimum number of upper case letters that must be met for a new password.