TestOut Linux Pro Practice Test 2025 - Free Linux Pro Practice Questions and Study Guide

The command that changes the runlevel to single-user mode is "systemctl isolate rescue.target." This command utilizes the systemctl tool to transition the system to the specified target, which, in this case, is the rescue target. The rescue target is designed for single-user mode, where only the essential services are started, allowing for maintenance tasks, troubleshooting, or recovery operations without the interference of multi-user services or graphical interfaces.

Using the isolate command effectively switches the current state of the system to the specified target immediately, making it the appropriate choice for changing to single-user mode. This operational method aligns with systemd's approach to managing system states through targets, providing a clean and clear method for system state changes.

The other commands listed serve different purposes. Setting a default target establishes what the system should boot into by default but does not immediately transition the system to that state. Starting a single-user target is also not the correct approach since the system may remain in its current state without isolating from other services. Enabling a target deals with making it available at boot time but does not affect the current state of the system.