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

amurleopard

Also see:
chage - change user password expiry information

       -M, --maxdays MAX_DAYS
           Set the maximum number of days during which a password is valid.
           When MAX_DAYS plus LAST_DAY is less than the current day, the user
           will be required to change their password before being able to use
           their account. This occurrence can be planned for in advance by use
           of the -W option, which provides the user with advance warning.

           Passing the number -1 as MAX_DAYS will remove checking a password's
           validity.

 -W, --warndays WARN_DAYS
	   Set the number of days of warning before a password change is required. The WARN_DAYS
	   option is the number of days prior to the password expiring that a user will be warned
	   his/her password is about to expire.

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 120 testuser

Check again.

$ sudo chage -l testuser
Last password change                                    : Mar 23, 2018
Password expires                                        : Jul 21, 2018
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