/etc/shadow stores actual password in encrypted format for user’s account with additional properties related to user password.
The password expiration information for a user is contained in the last 6 fields. Password expiration for a select user can be disabled by editing the /etc/shadow file
However I recommend using chage command. The chage command changes the number of days between password changes and the date of the last password change.
This information is used by the system to determine when a user must change his/her password.
To list current aging type chage command as follows:
# chage -l vivek
Last password change : August 23, 2013 Password expires : never Password inactive : never Account expires : never Minimum number of days between password change : 0 Maximum number of days between password change : 99999 Number of days of warning before password expires : 7
To disable password aging / expiration for user foo, type command as follows and set:
Minimum Password Age to 0
Maximum Password Age to 99999
Password Inactive to -1
Account Expiration Date to -1
Interactive mode command:
# chage username
# chage -I -1 -m 0 -M 99999 -E -1 username
- Understanding /etc/shadow file (robdurdle.com)