By default passwords do not expire on user accounts. If an expiration date has been added to an account and you wish to remove it, use the passwd command to change the maximum number of days between password changes to -1. This post describes how to turn off password aging when a maximum and possibly minimum value for password duration have been set.
Turn off a value for password duration by setting the number of days to -1.
# passwd -d tom tom 10/29/99 0 14
# passwd -x -1 tom Changing password for tom on geeklab.
# passwd -d tom tom