Under Linux password related utilities and config file(s) comes from shadow password suite. The /etc/login.defs file defines the site-specific configuration for this suite. This file is a readable text file, each line of the file describing one configuration parameter. The lines consist of a configuration name and value, separated by whitespace.

You need to set default password expiry using /etc/login.defs file (password aging controls parameters):

1. PASS_MAX_DAYS : Maximum number of days a password may be used. If the password is older than this, a password change will be forced.
2. PASS_MIN_DAYS : Minimum number of days allowed between password changes. Any password changes attempted sooner than this will be rejected
3. PASS_WARN_AGE : Number of days warning given before a password expires. A zero means warning is given only upon the day of expiration, a negative value means no warning is given. If not specified, no warning will be provided.

Open file /etc/login.defs using text editor:
# vi /etc/login.defs
Setup (sample) values as follows:
PASS_MAX_DAYS 30
PASS_MIN_DAYS 1
PASS_WARN_AGE 7
Close and save the file.

See also:

• Understanding /etc/shadow file
• Read man page of login.defs for more information.

Please note that much of the functionality that used to be provided by the shadow password suite is now handled by PAM suite. Next time I will write about PAM configuration.