Why does util-linux runuser (su) fork?
The `runuser` or `su` command in the util-linux package is used for switching to another user account on a Unix-like system. When a user runs `su`, it often appears that the command forks or spawns a new process. This behavior has a fundamental purpose and is linked to the way Unix-like systems handle user authentication and privilege separation. The process of forking in the context of `runuser` or `su` can be explained in detail: 1. **User Authentication:** When a user runs the `runuser` or `su` command, they typically want to execute commands or access resources with the privileges of a different user account. To do this, the system must perform user authentication to ensure that the user requesting the switch is allowed to become the target user. 2. **Password Verification:** Traditionally, the authentication process involves verifying the user's password. The user running `su` is asked to provide the password for the target user account. The system then needs to check if the