5.1. Finding the real devices

We will need this information later on, to be able to assign a given keyboard/mouse to a given X-server/Display.

To find the PHYS ID's (the addresses) or the name(quite oft it differs from the one labeled on the device) of your input devices you have to read the file /proc/bus/input/devices.

Here is what I have:

[svetljo@svetljo How-To]# cat /proc/bus/input/devices 
I: Bus=0011 Vendor=0002 Product=0002 Version=0034
N: Name="PS2++ Logitech Wheel Mouse"
P: Phys=isa0060/serio1/input0
H: Handlers=mouse0 ts0 
B: EV=7 
B: KEY=f0000 0 0 0 0 0 0 0 0 
B: REL=103 

I: Bus=0011 Vendor=0001 Product=0002 Version=ab02
N: Name="AT Set 2 keyboard"
P: Phys=isa0060/serio0/input0
H: Handlers=kbd 
B: EV=120003 
B: KEY=4 2000000 8061f9 fbc9d621 efdfffdf ffefffff ffffffff fffffffe 
B: LED=7 

I: Bus=0003 Vendor=046d Product=c303 Version=0700
N: Name="Logitech    USB Keyboard"
P: Phys=usb-00:10.1-1.1/input0
H: Handlers=kbd 
B: EV=120003 
B: KEY=10000 7f ffe00000 7ff ffbeffdf ffffffff ffffffff fffffffe 
B: LED=7 

I: Bus=0003 Vendor=046d Product=c303 Version=0700
N: Name="Logitech    USB Keyboard"
P: Phys=usb-00:10.1-1.1/input1
H: Handlers=kbd 
B: EV=100003 
B: KEY=1078 1800d100 1e0000 0 0 0 

I: Bus=0003 Vendor=05fe Product=0011 Version=0000
N: Name="Cypress Sem. PS2/USB Browser Combo Mouse"
P: Phys=usb-00:10.1-1.2/input0
H: Handlers=mouse1 ts1 
B: EV=7 
B: KEY=1f0000 0 0 0 0 0 0 0 0 
B: REL=103 

	Note
	/proc/bus/input/devices will provide the needed information for all devices except USB multimedia/office keyboards. For such USB multimedia/office keyboards you will have to gather additional information, for example with the help of lsusb. Under Ruby-2.6 for usb devices it will look like "usb-0000:00:10.x" not "usb-00:10.x"

• First we have to find the address of the USB keyboard:

  [root@svetljo How-To]# lsusb Bus 004 Device 001: ID 0000:0000 Bus 003 Device 001: ID 0000:0000 Bus 003 Device 002: ID 0409:55ab NEC Corp. Hub [iMac kbd] Bus 003 Device 003: ID 046d:c303 Logitech, Inc. Bus 003 Device 004: ID 05fe:0011 Chic Technology Corp. Browser Mouse Bus 002 Device 001: ID 0000:0000 Bus 001 Device 001: ID 0000:0000

  Here, my USB Logitech keyboard is Device 003 on Bus 003.

• Now we run lsusb with arguments -v -s [your USB keyboard device id in form Bus:Device], in my case, lsusb -v -s 003:003.

  ........ Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 3 Human Interface Devices bInterfaceSubClass 1 Boot Interface Subclass bInterfaceProtocol 1 Keyboard iInterface 0 ........ Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 3 Human Interface Devices bInterfaceSubClass 0 No Subclass bInterfaceProtocol 0 None iInterface 0 ........

So my USB keyboard has two interfaces (see bInterfaceNumber); the first one is the real keyboard (bInterfaceProtocol 1 Keyboard), the second (bInterfaceProtocol 0 None) - the additional keys. Hence the real USB keyboard is:

.....
N: Name="Logitech    USB Keyboard"
P: Phys=usb-00:10.1-1.1/input0
H: Handlers=kbd 
.....

The "P: Phys=" field (the physical descriptor/address) consorts of:

1. Bus type: "usb"

2. PCI function of the USB controller: "00:10.1 " ( for Ruby-2.6 "0000:00:10.1")

3. USB device id: "1.1"

4. The string: "/input"

5. Interface number: "0"