How do I change the minimum number of days between password change?

amurleopard

Also see:
chage - change user password expiry information

       -m, --mindays MIN_DAYS
           Set the minimum number of days between password changes to
           MIN_DAYS. A value of zero for this field indicates that the user
           may change their password at any time.

Check the user password expiry information.

$ sudo chage -l testuser
Last password change                                    : Mar 23, 2018
Password expires                                        : never
Password inactive                                       : never
Account expires                                         : Jan 08, 1970
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

Change the minimum number of days between password change to 30 days

$ sudo chage -m 30 testuser

Check again.

$ sudo chage -l testuser
Last password change                                    : Mar 23, 2018
Password expires                                        : never
Password inactive                                       : never
Account expires                                         : Jan 08, 1970
Minimum number of days between password change          : 30
Maximum number of days between password change          : 99999
Number of days of warning before password expires       : 7