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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. 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 007: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC
Bus 005 Device 006: ID 0403:6001 Future Technology Devices International, Ltd FT232USB-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 006 and 007. But if I pass /dev/bus/usb/005/006 to pyserial, which handles /dev/ttyUSBx just fine, I get SerialException("Could not open port: [Errno 13] Permission denied: '/dev/bus/usb/005/006'",).

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Have you tried "sudo chmod 666 /dev/bus/005/*"? – Max Ried Jun 14 '11 at 14:26

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