PAM: pluggable authentication modules for linux
http://www.linux-pam.org/whatispam.html
A suite of shared libraries that enable the local system administrator to choose how applications authenticate users.
/etc/pam.conf (or a series of configuration files located in /etc/pam.d/)
/lib/security or /lib64/security
一般Unix系统就是终端输入用户名和密码，到/etc/passwd中认证下，linux 中这种方法delicated了
PAM主要是配置管理4个方面：
authentication management;
account management;
session management;
password management
http://www.91ri.org/5157.html
原文：http://www.cnblogs.com/kuipertan/p/4381505.html