Issue
So, I'm trying to read a USB device in a brand new installation of Linux Mint.
The way I've done it before is to read the raw stream found in /dev/input/by-id
The device is being detected, and it is producing the expected device:
$ ls /dev/input/by-id/
usb-Generic_WebCam_SC-13HDL11939N_200901010001-event-if00
usb-Logitech_Logitech_Buzz_tm__Controller_V1-event-if00
But when I look at the file using
tail -f /dev/input/by-id/usb-Generic_WebCam_SC-13HDL11939N_200901010001-event-if00
No data is output to the terminal when I press some keys. I've tried it with sudo, I've tried changing the rights for the file. It basically waits where it is, unchanged.
There's a lot of questions about devices not appearing, or about IO errors when reading a file, but I can't find anyone else who's had the same problem.
Why might Linux Mint be detecting the device, but not reading the data from it?
Additional requested information:
# ls -lRa /dev/input/by-id
/dev/input/by-id:
total 0
drwxr-xr-x 2 root root 80 Jul 2 21:38 .
drwxr-xr-x 4 root root 360 Jul 2 21:38 ..
lrwxrwxrwx 1 root root 9 Jul 2 21:24 usb-Generic_WebCam_SC-13HDL11939N_200901010001-event-if00 -> ../event9
lrwxrwxrwx 1 root root 10 Jul 2 21:38 usb-Logitech_Logitech_Buzz_tm__Controller_V1-event-if00 -> ../event10
I tried tail -f on /dev/input/event10, too. Same result.
Also, the last few lines of dmesg
[ 263.440421] usb 2-1.1: new low-speed USB device number 5 using ehci-pci
[ 263.538270] usb 2-1.1: New USB device found, idVendor=054c, idProduct=0002
[ 263.538280] usb 2-1.1: New USB device strings: Mfr=3, Product=1, SerialNumber=0
[ 263.538285] usb 2-1.1: Product: Logitech Buzz(tm) Controller V1
[ 263.538290] usb 2-1.1: Manufacturer: Logitech
[ 263.585640] hidraw: raw HID events driver (C) Jiri Kosina
[ 263.597332] usbcore: registered new interface driver usbhid
[ 263.597338] usbhid: USB HID core driver
[ 263.615420] input: Logitech Logitech Buzz(tm) Controller V1 as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.1/2-1.1:1.0/0003:054C:0002.0001/input/input11
[ 263.668811] sony 0003:054C:0002.0001: input,hidraw0: USB HID v1.11 Joystick [Logitech Logitech Buzz(tm) Controller V1] on usb-0000:00:1d.0-1.1/input0
[ 811.582183] usb 2-1.1: USB disconnect, device number 5
[ 813.318275] usb 2-1.1: new low-speed USB device number 6 using ehci-pci
[ 813.416196] usb 2-1.1: New USB device found, idVendor=054c, idProduct=0002
[ 813.416207] usb 2-1.1: New USB device strings: Mfr=3, Product=1, SerialNumber=0
[ 813.416213] usb 2-1.1: Product: Logitech Buzz(tm) Controller V1
[ 813.416218] usb 2-1.1: Manufacturer: Logitech
[ 813.422041] input: Logitech Logitech Buzz(tm) Controller V1 as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.1/2-1.1:1.0/0003:054C:0002.0002/input/input12
[ 813.422335] sony 0003:054C:0002.0002: input,hidraw0: USB HID v1.11 Joystick [Logitech Logitech Buzz(tm) Controller V1] on usb-0000:00:1d.0-1.1/input0
I have found that it can be read using the evtest utility (https://wiki.ubuntu.com/DebuggingTouchpadDetection/evtest), but only as root, or using sudo.
Also as root or sudo, I am unable to see any data in the path mentioned above.
P.S. I am able to push control data to the lamps in these controllers via /sys/class/leds/
Solution
The problem here is with the tail program, not with the input devices themselves. tail is trying to read data until "the end of the file" before it starts printing anything -- but an input device has no "end of the file", so it will never print anything. cat, on the other hand, writes out data immediately as it comes in, so that works correctly. I don't know why tail worked for you with other input devices in the past.
Answered By - zwol