UsePAM

UsePAM is a configuration option in OpenSSH's sshd_config that controls whether the SSH server uses the Pluggable Authentication Modules (PAM) framework for authentication, account management, and session setup. When set to yes, sshd delegates these tasks to PAM and consults the PAM stack defined for the sshd service (typically in /etc/pam.d/sshd). When set to no, sshd performs authentication using its built-in methods and bypasses PAM for login attempts.

Enabling UsePAM allows administrators to apply centralized authentication policies implemented by PAM modules, such as password complexity requirements, account lockout policies, and integration with external systems like LDAP, Kerberos, or two-factor authentication. It also affects how password changes are handled and how session environment settings are applied through PAM. Disabling UsePAM can simplify configuration or reduce dependencies in environments that do not use PAM, but it disables the system-wide authentication policies managed by PAM for SSH logins.

Configuration and considerations: The option resides in the sshd_config file and is specified as a boolean value (yes or no). In many distributions, UsePAM is enabled by default to leverage PAM-based authentication. Changing the setting requires restarting the SSH daemon for the change to take effect. Potential issues include misconfigurations in the PAM stack for sshd, which can prevent logins or cause unexpected behavior if PAM modules are unavailable or improperly configured.