Which command would fail if executed on a service that is already stopped?

The command that would fail if executed on a service that is already stopped is the command associated with reloading the service configuration, which is commonly referred to as "service reload." When a service is not running, it lacks an active process to accept configuration changes or to reload its operational parameters.

A reload operation typically expects the service to be running so that it can update its configuration without interruption. When the service is stopped, there is no running instance available to process the reload command, resulting in an error.

In contrast, stopping an already stopped service, starting a service, or restarting a service does not encounter this issue. Stopping a service ensures it is already inactive, starting it initiates the service regardless of its previous state, and restarting it entails stopping it and then starting it, which also circumvents the problem since the stop command is followed by a start action.

Thus, the reload command is the only one that inherently requires the service to be actively running, which is why it would fail in this scenario.