I needed to configure a cisco switch, but I don’t have a COM port on my laptop. Fortunately I had a USB to serial convertor. When I tried connecting my Linux system to the switch using screen (screen /dev/tty.usbserial), I got the following errors:
Cannot open line '/dev/tty.usbserial' for R/W: Resource busy Sorry, could not find a PTY.
I could find a lot of information on the web that involved changing permissions on certain files. I tried that but it didn’t fix the problem. So I fiddled around a bit and found quite fast the cause of these errors. Apparently the screen process was already running, because I launched it before I installed the driver for the convertor. First, find the PID of the running process:
ps ax|grep -i screen 1093 .usb Ss+ 0:00.02 SCREEN /dev/tty.usbserial
Next, kill it:
sudo kill 1093
Try to invoke the command again. It should work now!