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How to use USB devices when USB drivers un available?

Postby chandranjoy » Wed Sep 01, 2010 8:41 pm

USB when the drivers aren't available

As a way to save a few valuable pennies on newer PCs, manufacturers are increasingly getting rid of the good old PS/2 keyboard and mouse interfaces. As a result, some recent systems only ship with USB ports to which we need to connect a USB keyboard and mouse.

USB is all good, but what if the driver for your USB controller is not loaded? In practice, this is not a problem, as Red Hat loads the ehci- hcd and uhci-hcd drivers automatically at boot time.

There are situations, namely in emergency mode, where the USB drivers won't be available. So you won't even be able to enter a command. This is due to the fact that in emergency mode all drivers need to be provided in the initrd file under /boot, and USB is not there by default. The trick is to add those drivers, so that they will be available earlier. The 'mkinitrd' command can do precisely that with the '--with' argument (this only works under RHEL4/CentOS 4 or later):
mkinitrd --with=ehci-hcd --with=uhci-hcd /boot/newinitrd-`uname -r`.img `uname -r`

Add a new entry in your grub.conf file (always do backups!) that points to this new initrd image, and you're done! Your USB keyboard now works in emergency mode.

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