I don't know if those are the correct Linux commands, but assuming they are, then yes, you should see something on the screen immediately if your serial port/cable is working properly and you boot the empeg. The empeg spends about 10 seconds spewing stuff to the serial port on every boot. Less if it doesn't have the player software installed yet, but you should see at least something on the serial cable even if the player doesn't have any disk drives attached or has just had the builder image installed.
Things I've seen that can cause the serial port to not work. Check each of these:
1. Serial port not correctly configured in the computer's BIOS.
2. Serial port not correctly configured in the computers operating system control panel.
3. A different software process is grabbing the serial port (such as PalmSync).
4. Bad/frayed cable.
5. Incorrect type of cable (see below).
6. COM port speed and settings on the computer are not set correctly to match the COM port speed and settings of the car player (see below).
Cable type and speed needed for the empeg:
1. If plugging into the empeg directly, you need a crossover serial cable, also called a NULL MODEM cable. This is a standard serial cable but with the TX and RX wires reversed. The computer's com port speed should be set to 115200, 8N1, No Flow Control.
2. If plugging into an empeg car docking sled, you need a "straight-through" serial cable (RX/TX are already swapped on the sled). Com port speed should be set to 4800, 8N1, No Flow Control. Also, if plugging into the sled, make sure the serial connector has a ground wire attached to the correct points; some older MK2 models were missing a ground wire on the sled serial connector.