I have a couple of FTDI based USB to Rs232 serial dongles. Sometimes when I plug them into my Ubuntu 10.04 laptop, they show up as /dev/ttyUSB0 and /dev/ttyUSB1, which is what I want to have happen. But sometimes they don't. When they don't, sometimes rebooting fixes the problem and sometimes it doesn't. They always show up in lsusb hanging off of Bus 5: Bus 005 Device 003: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC Bus 005 Device 002: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub I can see them if I do ls /dev/bus/usb/005 as 002 and 003. But if I pass /dev/bus/usb/005/002 to pyserial, which is what I'm using to access /dev/ttyUSBx, I get SerialException("Could not open port: [Errno 13] Permission denied: '/dev/bus/usb/005/002'",).