I hope this forum is still alive. I just found this and have followed the procedure for installing Prolific USB to Serial Adapter very carefully several times with mixed results. Usually when I do this the serial port does't work. The messages I get at end of dmesg are: [ 4955.155747] usb 7-1: USB disconnect, device number 6 [ 4955.156133] generic ttyUSB0: generic converter now disconnecteby hec1152 - RepRap Host