Why can't I connect to a parallel port target interface?

Failure to connect to parallel port target interfaces may be caused by the following problems:

• The user does not have read permission for the parallel port device driver (e.g. /dev/parport0). Linux typically does not grant all users access to the parallel port device drivers by default. To permit a user to access to the parallel port device drivers the user can either be added to the lp group, or alternatively the read permissions of the parallel port device driver can be changed to allow all users to have read access to it. Either of these actions require super user level permissions.
• Another application or device driver already has exclusive control of the parallel port device driver.

Why can't I connect the terminal emulator window to the serial port?

Failure to connect the terminal emulator window may be caused by the following problems:

• You do not have permission to use the serial port device driver (e.g. /dev/ttyS0). To permit a user to access the serial port either add the user to the uucp group, or change the permissions of the serial port device driver to enable all users to have access to it. Either of these actions require super user level permissions.
• Another application already has the serial port open.

Why can't I connect to a USB target interface?

Failure to connect to a USB target interface may be caused by the following problems:

• Incorrect version of libusb installed, download the latest version from http:://libusb.sourceforge.net and install it into the /lib directory.
• An entry is required in the /etc/hotplug/usb.usermap file for the USB device. This entry will associate a script with the USB VID and PID of the USB device. On RedHat Linux an entry will have the name of the script, a bitmask defining the number of fields to match and the fields to match. For example

  crossconnect 0x0003 0x131B 0x0001 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0 0x0

  will execute the script /etc/hotplug/usb/crossconnect when a USB device with VID 0x131B and PID 0x0001 is connected. The script that is executed should enable user access to the USB device. For example the script

  #!/bin/bash
        if [ "${ACTION}" = "add" ] && [ -f "${DEVICE}" ]
        then
          chmod a+rw "${DEVICE}"
        fi

  enables user access to a USB device on RedHat Linux.