Which file on a Linux system is modified to set the maximum number of days before a password must be changed?

The file responsible for managing user account information, including password expiration settings, is /etc/shadow. This file contains hashed passwords and relevant account attributes for users, such as the maximum number of days before a password must be changed, minimum password age, and more. By modifying the contents of /etc/shadow, system administrators can enforce policies regarding password lifespan, helping to enhance security by ensuring users update their passwords within a specified timeframe.

In contrast, /etc/passwd contains basic user account information but does not hold password expiration data. The /etc/groups file lists the groups on the system and their members, while /etc/users is not a standard file on Linux systems. Hence, /etc/shadow is the correct choice for configuring password expiration policies.