Brand new MBP running latest MacOS Catalina 10.15.1, using USB-C to serial device found here:

Get following errors in quick succession when attempting to use the screen command:

Cannot open line '/dev/ttyUSBtoSerial for r/w: resource busy
Sorry, could not find a PTY

Things I have tried:

Adding my user to dialer, tty, and wheel group (Some googling suggested adding user to dialout group but could not find said group on my mac).

Manually installing D2XX drivers found from amazon page.

Verified no screen sessions were still opened with Activity Monitor.

Verified proper permissions were set on the tty device itself.

Coworker was able to use same cable on a MBP successfully.



Job #1 - is to determine if the USB device is being recognized in any form, you can do that by looking for the USB VID and PID (described below). When you plug the cable in, you should see the device appear in the list, and go away when you unplug.

The VID number will tell you the ACTUAL chip type, ie: FTDI, SiLAB, Prolific, or Microchip there are many chips in these cables. Your comments imply you believe this is an FTDI cable, this will confirm. Otherwise you are going after the WRONG driver.

Job #2 - Using the VENDOR ID - determine if the driver is loaded or not, or is present. For example once you confirm it is an FTDI cable, then the existing Apple provided driver should be present, same with SiLABs (apple provides this driver).

To do the above:

First verify that this is an FTDI cable, there are many other chips (Microchip, SiLab, and Prolific) - some vendors (example: Adafruit, and others) have been known to change the chip inside with different cable builds.

The GUI method on macOS is: 🍎 -> About this Mac -> System Report, under hardware click on USB.

There are multiple "root hubs" - my MacPro has a total of 5 (some hubs are built in and hidden inside your Mac and not exposed externally)

Plug & Unplug your device, in the menubar of System Information -> File -> Refresh (CMD-R) to update the list displayed.

Look for the "Vendor ID (VID)" (who makes the USB device) and "Product ID (PID)". for example FTDI = VID: 0403, PID = 6010 (for the FTD2232H, the PID might vary depending on the chip).

As an alternative you can open Terminal and type: ioreg -p IOUSB -l -w 0 and get a lot of of details.

You can do the same thing with Windows in the Device Manager. On Linux, you can use lsusb to print the USB devices.

This will verify that your device is even "half recognized".

Part 1 - is that the OS can find the VID and PID

Part 2 - is the driver for that USB device

Note that FTDI has a built in driver in Catalina, no external driver required.

  • Can you please edit your post to focus on your actual recommendation on how to solve the problem? Right now it‘s a bit hard to understand
    – nohillside
    Dec 2 '19 at 13:23
  • Edited per your request Dec 2 '19 at 15:32

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