What is the command used to stop a designated unit?

The command used to stop a designated unit in a system that employs systemd as its init system is "systemctl stop." This command is utilized to stop a service or target unit, effectively halting its operation without shutting down or rebooting the entire system.

When you execute "systemctl stop [unit-name]," you tell the systemd manager to terminate the specified unit, which could be a service like a web server or a database. This is critical in managing services on a Linux system, allowing administrators to start, stop, reload, or check the status of services as needed, providing flexibility in system management and resource control.

The other options do not serve the purpose of stopping a service. For example, "systemctl halt" is used to halt the entire system, while "systemctl exit" and "systemctl finish" are not valid commands in this context. Understanding the specific use of the "stop" command is vital for effective service management in a Linux environment.