device /dev/ttyusb0 lock failed: operation not permitted

I found I was able to fix the situation on my CentOS box by running minicom -S <device> -o and the do the normal exit key sequence (CTRL-a, x).

In your situation it would have been

sudo minicom -S ttyusb0 -o

This cleared the lock files minicom had placed in /var/lock/

Good luck Ash

I ran into a similar issue with using gtkterm from a remote terminal. I had shutdown the terminal without explicitly terminating gtkterm. The result was that subsequent gtkterm sessions gave me the error:

Device /dev/ttyUSB0 is locked.

Checking the process list via ps did not show any gtkterm processes still running.

I corrected this by simply deleting /run/lock/LCK..ttyUSB0. After doing that, gtkterm was able to open ttyUSB0 successfully.