188.8.131.52.1. Stacking Module Interfaces
Module interface directives can be
, or placed upon one another, so that multiple modules are used together for one purpose. If a module's control flag uses the "sufficient" or "requisite" value (refer to Section 184.108.40.206, “Control Flag”
for more information on these flags), then the order in which the modules are listed is important to the authentication process.
Stacking makes it easy for an administrator to require specific conditions to exist before allowing the user to authenticate. For example, the
reboot command normally uses several stacked modules, as seen in its PAM configuration file: