Authentication fails

[pam-list@redhat.com (Ion Badoi)]

I set PAM authentication with RedHat 7.2 via /etc/passwd.
Why can't users authenticate?
At command squid -NCd1 the answer is: too few authenticator processes
are running
In /var/log/messages: PAM unable to dlopen(/lib/security/pam_unix.so)

Thanks!