Which FortiGate command can be used to reset the device to factory defaults?

Using the command "exec factoryreset" is indeed the correct method to reset a FortiGate device to its factory defaults. When this command is executed, it initiates a process that clears all configurations and restores the device to its original state as it was when first received. This is crucial for scenarios where complete reconfiguration is needed or if the device is being prepared for a different environment.

The command directly specializes in handling the reset operation without confusing it with other commands that may have different outcomes. It clearly indicates the action of factory resetting, making it straightforward for administrators who need to perform this task.

In contrast, options like "reset factory" do not exist as a valid command in FortiGate’s CLI, which makes it evident that it's not a recognized method for resetting the device. Similarly, "system reset" and "clear configuration" can imply different functionalities—such as resetting system parameters or clearing specific configurations—rather than removing all settings entirely. Hence, utilizing "exec factoryreset" is the most effective and direct approach to ensure full restoration to factory conditions.