有时候我们的测试机器，只想设置个简单的密码，例如 hello 
但是这时候系统会报错

New Password: 
passwd: Password too short - must be at least 6 characters.
New Password: 
passwd: The password must contain at least 1 numeric or special character(s).

此时需要更改配置文件/etc/default/passwd 文件：
MAXWEEKS=
MINWEEKS=
PASSLENGTH=5

#MINDIFF=3
#MINALPHA=2
#MINNONALPHA=1
MINUPPER=0
MINLOWER=0
#MAXREPEATS=0
MINSPECIAL=0
MINDIGIT=0