How do I free a busy tty device?

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How do I free a busy tty device?

Question:

Using the 'screen' command in terminal, I get the error "cannot open line '/dev/tty.usbserial' for R/W: resource busy". How do I release or free this resource?

Background:

I am connecting to a Raspberry Pi UART via a MAX3232 serial to TTL converter module. The RS232 serial port on my iMac is provided via a Prolific USB to Serial adaptor. Using a terminal window, I entered "screen /dev/tty.usbserial 115200". The first time I did this,and booted the raspberry pi, i got many beeps and scrolling blank spaces (eg there was some sort of connection, good). I then didn't know how to exit screen, so I command Q'd the session. Now when i re-open the session, and use 'screen' again, I get the error as stated above. I realise turning it off and on again will probably do it, but am after a commnad.

Cheers,

Les.

iMac, OS X Mavericks (10.9.2)

Posted on Apr 10, 2014 6:38 PM

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Answer 1

Top-ranking reply

Sefi G

Level 1

5 points

Jun 14, 2014 1:38 PM in response to Les 76

From terminal, run:

lsof | grep usbserial

If the port is in use, you will get a response like this (otherwise it will return nothing):

screen 27127 Sefi 5u CHR 18,0 0t0 605 /dev/tty.usbserial

Note the session number. In my case, it's 27127. Then run:

screen -x 27127 (obviously use your session number from the grep)

It will return you to your previous screen session. Then use ctr-A ctr-\ to close it properly (will ask you to confirm).

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Answer 2

Oct 30, 2017 12:50 PM in response to Les 76

I realize that this is several years old now, but I just ran into this today. To fix the resource busy message, you should be able to go to activity monitor and terminate the "screen" processes. This will release the screen process for you to be able to connect again.

I ran into the same problem with the blank screen as well. I was usually able to hit the enter key enough times and it would eventually show me a login prompt. I think a bad cable or interface is typically the issue with the serial connection but I can't be sure about that one.

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