□ When linux is installed, like the picture above, there is a case that the password is stored in the passwd file
□ If the password policy is changed to shadow, each account's password of password file is changed to x
□ pwconv : It is linux command to change password policy(passwd → shadow)
□ pwunconv : It is linux command to change password policy(shadow → passwd)
It is also posted at here : http://cysecguide.blogspot.com/2016/09/method-of-changing-password.html