Which command would you use if you want to trigger device events within udev?

The appropriate command to trigger device events within udev is "udevadm trigger." This command is specifically designed to instruct udev to process existing devices in the system and generate events for them as if they had just been added or removed. When you run this command, it essentially re-evaluates the current hardware devices and can apply rules defined in the udev configuration files, which can be beneficial for reapplying device changes without needing to physically remove or add hardware.

The command operates by examining the current state of devices in the system and applies the relevant actions based on the rules set up for those devices. This can be particularly useful for scenarios where you may have changed configurations or want to restart or refresh device handling without rebooting the system or recompiling configurations.

The other options do not exist or are not related to triggering device events in udev. For example, the command intended to start udev (which doesn't exist) is misrepresented in the first choice, while the others also do not correspond with actual udev commands recognized by the system. Therefore, "udevadm trigger" stands out as the correct answer based on its functionality regarding device event handling.