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44.12. USB Configuration

Many PCs support the Universal Serial Bus (USB). USB is a hot-swappable standard; devices can be plugged in and unplugged while the machine is running, and the system is supposed to recognize the new device or no longer recognize the now disconnected device.

Unixes deal with this requirement with low-level device drivers to actually interface with the devices and with a daemon, usbd, to monitor for changes on the fly or, on Linux, the hotplug facility (http://linux-hotplug.sourceforge.net).

Generally, there is very little configuration required for supported USB devices. If you have the correct kernel modules (Section 44.3) loaded (and on many platforms they're loaded by default), just plug in the device. Check your platform's supported hardware before buying a USB device, as such devices are changing rapidly at the time of this writing and may or may not have Unix drivers implemented yet.

Specific issues you might run into include that USB disks may need to use a special filesystem type (usbdevfs) and that specific devices may require tools to actually use the device. Webcams and scanners are a good example, as the device driver provides only low-level access to the device; you still need a tool that can pull images off of the device and do something useful with them. Extensive information is available on the Web about using many USB devices on the free Unixes (http://www.linux-usb.org for Linux and the USB chapter in the FreeBSD handbook are places to start), and it stays fairly up to date.


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