How do I disable a linux account?

[amurleopard]

Also see:
chage - change user password expiry information

-E, --expiredate EXPIRE_DATE
	   Set the date or number of days since January 1, 1970 on which the user's account will
	   no longer be accessible. The date may also be expressed in the format YYYY-MM-DD (or
	   the format more commonly used in your area). A user whose account is locked must
	   contact the system administrator before being able to use the system again.

	   Passing the number -1 as the EXPIRE_DATE will remove an account expiration date.

This will disable the user account.

$ chage -E0 testuser

This will disable all method of access by Linux Pluggable Authentication Modules (PAM). For information on PAM see this wikepedia link: https://en.wikipedia.org/wiki/Linux_PAM