Linux Server Hacks, Volume Two

Hack #4. Customize Authentication with PAMs

Modern Linux systems use Pluggable Authentication Modules (PAMs) to provide flexible authentication for services and applications. Here are the gory details you'll need in order to use PAMs to quickly and flexibly secure your systems.

Many Linux applications require authentication of one type or another. In days gone by, each authentication-aware application was compiled with hardwired information about the authentication mechanism used by the system on which it was running. Changing or enhancing a system's authentication mechanism therefore required all such applications to be updated and recompiled, which is tedious even when you have the source code for all of the relevant applications on your system.

Enter PAMs, which provide a flexible and dynamic mechanism for authenticating any application or service that uses them. Applications or services compiled with the Linux-PAM library use text-format configuration files to identify their authentication requirements. Using PAMs on your system lets you modify authentication requirements or integrate new authentication mechanisms by simply adding entries to the PAM configuration file that is used by a specific application or service.

Though the information contained here may seem like overkill at first glance, knowing about PAMs and how PAM configuration files work is necessary background for the next four hacks, which explain how to integrate specific types of modern authentication into your ...