Problem with Plugable USB/Serial on Macbook Pro 10.11.5


I just installed my new Plugable USB/Serial adapter onto my Macbook Pro running 10.11.5. Installation seems to have gone ok. I used the drivers from the plugable site (PL2303_1.6.0_20151012.pkg)

After a fresh reboot of my mac, I’m able to use the adapter to connect to a device’s serial port (a Cisco ASA firewall) using this command:
screen /dev/cu.usbserial 9600

Here’s an example of the processes that are running after using screen after a fresh reboot:
$ ps -ef | grep usbserial
501 1139 723 0 2:42PM ttys000 0:00.00 grep usbserial
501 1052 1031 0 2:42PM ttys001 0:00.01 screen /dev/cu.usbserial 9600
501 1053 1052 0 2:42PM cu.usbserial 0:00.04 SCREEN /dev/cu.usbserial 9600

But, then I close that screen window (by closing the iTerm2 window/tab or by issuing in the screen window CTRL-A then CTRL-\ and entering y).

Now, when I try to run screen again, the screen command returns nothing. And, the screen processes become hung. I cannot even kill those processes. I have to do a hard power-cycle of my mac. Which leads me back to square one.

Here’s an example of the processes that are running that I cannot kill:
$ ps -ef | grep usbserial
501 1460 1459 0 2:45PM ?? 0:26.89 SCREEN /dev/cu.usbserial 9600
501 1507 723 0 2:45PM ttys000 0:00.00 grep usbserial
501 1459 1433 0 2:45PM ttys002 0:00.01 screen /dev/cu.usbserial 9600

Can someone help?


I just searched for a solution and found the info in the following link.…

I’ll try out the workaround when I get a chance.


Hi WW,

Thank you very much for sending the link to a solution. Could you please post again about how it worked?


David Plugable Support


Yes, this command worked for me (repeatedly).
sudo cu -l /dev/cu.usbserial -s 9600

I did not try the other suggestion from the above link (the one about doing “stty clocal < /dev/cu.usbserial”).

I have no idea where the fault lies when trying to use the screen command.


Hi WW,

Thanks for the information. I’m going to close this thread. If you have any other comments or questions, please contact us directly at Thanks!