PAM, pam − Pluggable Authentication Modules for Linux
This manual is intended to offer a quick introduction to Linux−PAM. For more information the reader is directed to the Linux−PAM system administrators' guide.
Linux−PAM is a system of libraries that handle the authentication tasks of applications (services) on the system. The library provides a stable general interface (Application Programming Interface − API) that privilege granting programs (such as login(1) and su(1)) defer to to perform standard authentication tasks.
The principal feature of the PAM approach is that the nature of the authentication is dynamically configurable. In other words, the system administrator is free to choose how individual service−providing applications will authenticate users. This dynamic configuration is set by the contents of the single Linux−PAM configuration file /etc/pam.conf. Alternatively, the configuration can be set by individual configuration files located in the /etc/pam.d/ directory. The presence of this directory will cause Linux−PAM to ignore/etc/pam.conf.
From the point of view of the system administrator, for whom this manual is provided, it is not of primary importance to understand the internal behavior of the Linux−PAM library. The important point to recognize is that the configuration file(s) define the connection between applications (services) and the pluggable authentication modules (PAMs) that perform the actual authentication tasks.
Linux−PAM separates the tasks of authentication into four independent management groups: account management; authentication management; password management; and session management. (We highlight the abbreviations used for these groups in the configuration file.)
Simply put, these groups take care of different aspects of a typical user's request for a restricted service:
account − provide account verification types of service: has the user's password expired?; is this user permitted access to the requested service?
authentication − authenticate a user and set up user credentials. Typically this is via some challenge−response request that the user must satisfy: if you are who you claim to be please enter your password. Not all authentications are of this type, there exist hardware based authentication schemes (such as the use of smart−cards and biometric devices), with suitable modules, these may be substituted seamlessly for more standard approaches to authentication − such is the flexibility of Linux−PAM.
password − this group's responsibility is the task of updating authentication mechanisms. Typically, such services are strongly coupled to those of the auth group. Some authentication mechanisms lend themselves well to being updated with such a function. Standard UN*X password−based access is the obvious example: please enter a replacement password.
session − this group of tasks cover things that should be done prior to a service being given and after it is withdrawn. Such tasks include the maintenance of audit trails and the mounting of the user's home directory. The session management group is important as it provides both an opening and closing hook for modules to affect the services available to a user.
/etc/pam.conf
the configuration file
/etc/pam.d
the Linux−PAM configuration directory. Generally, if this directory is present, the /etc/pam.conf file is ignored.
Typically errors generated by the Linux−PAM system of libraries, will be written to syslog(3).
DCE−RFC 86.0, October 1995. Contains additional features, but remains backwardly compatible with this RFC.
pam(3), pam_authenticate(3), pam_sm_setcred(3), pam_strerror(3), PAM(8)
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.