USB-Serial adaptor on Mac OS X

I have a USB-Serial adaptor (prolific pl2303 chip) and MBP Mac OS 10.11.4 for connecting to console of switches, routers and firewalls via screen. Since somewhere between Mac OS 10.11.2 and 10.11.3, the setup is broken as screen will hang if I exit the screen session and then try to reconnect to the device via USB-Serial adaptor. I did upgrade to the latest firmware from prolific page for Mac but did not help…So I started posting for help on Internet forums…

janm on Stack Exchange really helped. Here is the workarounds: use cu instead of screen on Mac for the task. The catch though is by default cu needs to be run with sudo. So,

  1. Type in the password everytime you try to connect to console.
  2. Use one of the followings to get rid of the password prompts:

OPTION 1: Create cu configuration file like “/Users/test/cu.conf” with content below and also create the lock folder accordingly. Run the cu command as “cu -I /Users/test/cu.conf -l /dev/cu.usbserial -s 9600 –nostop

lockdir /Users/test/cu_lockdir

OPTION 2(HIGHLY NOT Recommended): Run “sudo visudo” and uncomment the line below and save and exit.

 %wheel ALL=(ALL) NOPASSWD: ALL

BTW, I also opened a bug report with Apple and provided necessary debug but have not heard back yet…I think the screen compiled with Mac OS X changed on handling port open/close.

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