/etc/pam.d/su

This file is used by the PAM (Pluggable Authentication Modules) system in Linux to configure the authentication policies for the su command. The su command is used to switch to another user account, usually the root user, in order to perform administrative tasks.

The /etc/pam.d/su file contains a set of rules that determine which authentication modules are used to authenticate the user when they run the su command. These rules can include requirements such as the use of a strong password, the presence of a valid user account, or the use of two-factor authentication.

The file typically contains a series of lines, each of which corresponds to a particular PAM module or set of modules. These modules are called in order, with each module providing a different type of authentication check. Each line specifies the name of the module, any parameters it requires, and whether or not it is required for authentication to be successful.

The /etc/pam.d/su file is an important part of securing a Linux system, as it determines who is allowed to run the su command and what authentication checks are required. It should be configured carefully to ensure that only authorized users are able to access administrative privileges on the system.