In Linux, understanding the concept of user identities (UIDs) is crucial for ensuring both security and appropriate access controls. There are several types of UIDs that Linux utilizes to manage process permissions: Real UID (RUID), Effective UID (EUID), Saved Set-User-ID (SUID), and Filesystem UID (FSUID). Each of these IDs plays a specific role in determining how a process interacts with the operating system and accesses resources.
- Real UID (RUID): This represents the actual user who initiated a process. The RUID is primarily used to identify the owner of the process for purposes like process management and accounting. It is a crucial component for auditing and tracking user activities.
- Effective UID (EUID): The EUID is critical for access control and permissions checks. It determines the access rights a process has for performing various operations. Notably, when a process runs a file with the SUID bit set, its EUID is temporarily set to the owner of the file, allowing it to perform actions with the permissions of that user.
- Saved Set-User-ID (SUID): This UID is a special type of identifier that a process uses to switch between user privileges. It allows a process to elevate its privileges (typically to root) to perform specific tasks and then revert to its original permissions. This mechanism is essential for programs that require higher…
