Using 'su' without specifying a username defaults to which user?

• A. Root user
• B. Guest user
• C. Admin user
• D. Current user

Answer: (A)

When the 'su' command is executed without specifying a username, it defaults to switching to the root user. This is a fundamental aspect of Unix-like operating systems, where 'su' stands for "substitute user." The root user is the superuser account that has full control over the system, allowing for administrative tasks that regular users cannot perform.

This functionality emphasizes the importance of having root access, as it is essential for performing system-level operations such as software installation, system configuration changes, and managing user permissions.

Additionally, the absence of a specific username in the 'su' command means the system assumes that the intent is to access the root account, underscoring the command's primary purpose of privilege escalation in administrative contexts. As a result, using 'su' without any arguments directs the command to the root, which is critical for system administrators and anyone needing full system access.