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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, 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'",).

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Don't access /dev/bus/usb/* with pyserial It is a direct connection to your USB device so you need to talk USB to it, not serial.. –  Source Lab Sep 23 '10 at 12:42
    
@Source - makes sense. Thanks! –  mtrw Sep 24 '10 at 8:02
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up vote 3 down vote accepted

If you don't need the serial device for braille devices, you may wish to disable brltty (you can remove the package), which used to be the culprit for ttyUSB devices at least before Lucid.

I definitely hadn't seen USB RS232 dongles still get claimed by brltty since the Lucid release though.

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This is a pretty common issue among Arduino uC developers. –  Evan Plaice Sep 23 '10 at 13:06
    
Thanks for the tip. I'll try it the next time I see the problem and accept your answer then. –  mtrw Sep 24 '10 at 8:03
    
I went ahead and removed the brltty package and things seem to work. @Evan - the USB device in question is based on an FTDI interface, which I think is what's used in Arduino too. Maybe there's an issue specific to that USB chip. –  mtrw Sep 27 '10 at 22:20
    
@mtrw Arduino does use the FTDI chip as it's serial/USB interface. –  Evan Plaice Oct 5 '10 at 18:31
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