Module paths tell PAM where to find the pluggable module to be used
with the module type specified. Usually, it is provided as the full
path to the module, such as
/lib/security/pam_stack.so. However, if the full
path is not given (in other words, the path does not start with a
/), then the module indicated is assumed to be in
the /lib/security/ directory — the default
location for PAM modules.
