To effectively disable a Linux user account so that it can't login using its password or keys, you can use the
Lock a Linux user
# usermod -e 0000-00-00 -L zma2
Unlock the user locked by the above one:
# usermod -e "" -U zma2
-U options lock/unlock the user's password and
-e set/clear the expiration dates so that the user can/cannot login using other ways than the password.