Understanding: /etc/shadow (User Account Management)

RHCSA exam focus on basic system administration, and questions asked in RHCSA are similar situations which you will face in real environment.

     /etc/shadow is not commonly used file, but is very important as far as User Administration and RHCSA is concern.

    /etc/shadow contains password related information for user and groups on the system. This file stores actual password in encrypted format for user's account with additional properties related to user password.

An example entry of /etc/shadow is given below:

rajesh:$1$J6/rsxw3$TEcDpPsW0gx9035DFNlUU/:15162:0:99999:7:::

Each entry in /etc/shadow contains 9 fields.

/etc/shadow

1. Username: It is used when user log-in. It should be between 1 to 32 character.
2. Password: It is a user's encrypted password. The password should be minimum of 6 to 8 characters long including special characters/digits.
3. Days since Unix epoch password was changed (Jan 1 1970).
4. Minimum: Days left before password may be changed.
5. Maximum: days after which password must be changed.
6. Warn: The days before password is to expire, that user is warned that his/her password must be changed.                                                                   
7. Inactive: The days after password expires, that account is disabled.
8. Days since Unix epoch, that account is disabled.
9. Reserve field (currently unused) .

Using this file you can manage password properties.