NewsForge: Hardening Linux Authentication and User Identity

“PAM is an authentication mechanism that originated on Solaris,
but is used on various systems, including Linux. The Linux PAM
implementation allows a system administrator to choose how users
authenticate to various services. New modules can be added by an
administrator at any time, offering overall flexibility in how
authentication happens.

“Traditionally, Linux and other Unix-like systems simply
authenticated users against an entry in the file /etc/passwd.
Everyone had read-only access to the password file, and the
encrypted passwords were available to anyone with access to the
system…”

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