In Linux, what does the command 'shutdown -h now' do?

The command 'shutdown -h now' is used in Linux to halt, or stop, the system immediately. When you execute this command, it initiates a graceful shutdown process that ensures all running services are stopped, filesystems are unmounted, and active processes are terminated cleanly. The '-h' option specifically tells the system to halt the operation, which means it will stop all CPU functions and power down the hardware, depending on the system configuration.

This command is crucial for safely shutting down a machine without risking data corruption or loss. In contrast, commands that involve rebooting or changing the runlevel do not serve the purpose of simply halting the system, which is why those responses would not be applicable in this context.