# PAM - Pluggable Authentication Modules
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### Basic Information
**PAM (Pluggable Authentication Modules)** acts as a security mechanism that **verifies the identity of users attempting to access computer services**, controlling their access based on various criteria. It's akin to a digital gatekeeper, ensuring that only authorized users can engage with specific services while potentially limiting their usage to prevent system overloads.
#### Configuration Files
* **Solaris and UNIX-based systems** typically utilize a central configuration file located at `/etc/pam.conf`.
* **Linux systems** prefer a directory approach, storing service-specific configurations within `/etc/pam.d`. For instance, the configuration file for the login service is found at `/etc/pam.d/login`.
An example of a PAM configuration for the login service might look like this:
```
auth required /lib/security/pam_securetty.so
auth required /lib/security/pam_nologin.so
auth sufficient /lib/security/pam_ldap.so
auth required /lib/security/pam_unix_auth.so try_first_pass
account sufficient /lib/security/pam_ldap.so
account required /lib/security/pam_unix_acct.so
password required /lib/security/pam_cracklib.so
password required /lib/security/pam_ldap.so
password required /lib/security/pam_pwdb.so use_first_pass
session required /lib/security/pam_unix_session.so
```
#### **PAM Management Realms**
These realms, or management groups, include **auth**, **account**, **password**, and **session**, each responsible for different aspects of the authentication and session management process:
* **Auth**: Validates user identity, often by prompting for a password.
* **Account**: Handles account verification, checking for conditions like group membership or time-of-day restrictions.
* **Password**: Manages password updates, including complexity checks or dictionary attacks prevention.
* **Session**: Manages actions during the start or end of a service session, such as mounting directories or setting resource limits.
#### **PAM Module Controls**
Controls dictate the module's response to success or failure, influencing the overall authentication process. These include:
* **Required**: Failure of a required module results in eventual failure, but only after all subsequent modules are checked.
* **Requisite**: Immediate termination of the process upon failure.
* **Sufficient**: Success bypasses the rest of the same realm's checks unless a subsequent module fails.
* **Optional**: Only causes failure if it's the sole module in the stack.
#### Example Scenario
In a setup with multiple auth modules, the process follows a strict order. If the `pam_securetty` module finds the login terminal unauthorized, root logins are blocked, yet all modules are still processed due to its "required" status. The `pam_env` sets environment variables, potentially aiding in user experience. The `pam_ldap` and `pam_unix` modules work together to authenticate the user, with `pam_unix` attempting to use a previously supplied password, enhancing efficiency and flexibility in authentication methods.
### References
* [https://hotpotato.tistory.com/434](https://hotpotato.tistory.com/434)
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