Linux environment key detection

When I recently upgraded labwc to v0.6.5, I found that the screenshot button print had no response no matter how I pressed it.

reasons may be:

  • The linked screenshot software failed;
  • The button is broken;
  • Problems caused by upgrading labwc.

The screenshot software I use is a combination of grip + slurp + ksnip, which is implemented by calling the script. There is no problem in actual testing.

5NOW=$(date +"%Y-%m-%d-%H%M%S")
6grim -g "$(slurp )" -t png $HOME/Pictures/grim-$NOW.png
7QT_QPA_PLATFORM=xcb /usr/bin/ksnip $HOME/Pictures/grim-$NOW.png

Could it be that the button is broken? My equipment costs ¥1800. Each button is worth a few dollars at least. It can’t fail so easily!

The question is, how to detect whether the print key is valid in a Linux environment? At this time, I thought of xev and wev, which correspond to event detection under the X and Wayland environments respectively. The tragedy is that when using these two command line tools to detect, nothing is output when the print button is pressed. I even flipped the keycap and pressed it, but nothing happened!

In desperation, I could only roll back to labwc. After logging in again, everything was normal. This is a big joke, there is this magical problem, targeting specific buttons and sniping at fixed points.

Ordinary people may not pursue it at this time, but when I go to bed at night, I am thinking, how can I easily detect that the button is valid?

Summarized as follows:

1. Use xev and wev

The X environment uses xev, and Wayland uses wev. Although my problem cannot be detected due to special unknowns, it is still very useful.

As shown below, I pressed the key next to Enter and 1 (it's called grave, I found out by looking at the output below 😊) The core information of the button, such as button name, key, etc., will be displayed in real time. One item will be displayed each when pressed and released.

 1➜ ~wev
 2[07: wl_seat] name: seat0
 3[07: wl_seat] capabilities: pointer keyboard
 4[10: xdg_toplevel] configure: width: 0; height: 0
 5[09: xdg_surface] configure: serial: 39874
 6[14: wl_keyboard] keymap: format: 1 (xkb v1), size: 63738
 7[14: wl_keyboard] repeat_info: rate: 25 keys/sec; delay: 600 ms
 8[14: wl_keyboard] enter: serial: 39879; surface: 3
 9' sym: Return (65293), utf8: '
10[14: wl_keyboard] modifiers: serial: 0; group: 0
11                       depressed: 00000000
12                       latched: 00000000
13                       locked: 00000000
14[11: wl_data_device] data_offer: id: 4278190080
15[4278190080: wl_data_offer] offer: mime_type: TEXT
16[4278190080: wl_data_offer] offer: mime_type: text/plain
17[4278190080: wl_data_offer] offer: mime_type: text/plain;charset=utf-8
18[4278190080: wl_data_offer] offer: mime_type: STRING
19[4278190080: wl_data_offer] offer: mime_type: UTF8_STRING
20[11: wl_data_device] selection: id: 4278190080
21[13: wl_pointer] enter: serial: 39882; surface: 3, x, y: 197.863281, 79.218750
22[13: wl_pointer] frame
23[10: xdg_toplevel] configure: width: 0; height: 0
24                       activated
25[09: xdg_surface] configure: serial: 39877
26[14: wl_keyboard] key: serial: 39883; time: 24157739; key: 36; state: 0 (released)
27                       sym: Return (65293), utf8: ''
28[14: wl_keyboard] key: serial: 39884; time: 24162044; key: 49; state: 1 (pressed)
29                       sym: grave (96), utf8: '`'
30[14: wl_keyboard] key: serial: 39885; time: 24162200; key: 49; state: 0 (released)
31                       sym: grave (96), utf8: ''
32[14: wl_keyboard] key: serial: 39886; time: 24172492; key: 36; state: 1 (pressed)
33' sym: Return (65293), utf8: '
34[14: wl_keyboard] key: serial: 39887; time: 24172621; key: 36; state: 0 (released)
35                       sym: Return (65293), utf8: ''
36[14: wl_keyboard] key: serial: 39888; time: 24183338; key: 49; state: 1 (pressed)
37                       sym: grave (96), utf8: '`'
38[14: wl_keyboard] key: serial: 39889; time: 24183480; key: 49; state: 0 (released)

2. Use showkey command

If you have entered the system graphical interface, you need to run sudo showkey, as shown below. 99 is the print key.

 1➜ ~ sudo showkey
 2[sudo] password for mephisto:
 3kb mode was ?UNKNOWN?
 4[ if you are trying this under X, it might not work
 5since the X server is also reading /dev/console ]
 7press any key (program terminates 10s after last keypress)...
 8keycode 28 release
 9keycode 99 press
10keycode 99 release
11keycode 99 press
12keycode 99 release
13keycode 1 press
14keycode 1 release

If you are in the terminal environment (you can press Ctl + Alt + F1-F7, F1-F7 to select one to switch to the terminal environment for testing), enter the password and run it directly without sudo. At this time, any keystrokes will be intercepted and you can only wait 10 seconds to exit automatically. I have never experienced this before.

In other words, showkey is the ultimate trick. It is not affected by various environments and can be used to detect whether the keys are physically damaged.

Some people may ask, shouldn't it be better if I just find a place where I can type characters and see if the characters on the screen are correct? This cannot detect various function keys such as print.

Some people will say that I am an embedded engineer and it is indeed possible to write programs to detect and solve problems. But showkey has been around for a long time, and it doesn’t waste time to use it.

In summary, use xev and wev for simple keyboard detection, and showkey in special cases.

Finally, the screenshot triggered by the new version of labwc is invalid. It is estimated that there is an exception when the script is added. There is no simple debugging method, so roll back to solve it first. labwc is a binary program, and it is not troublesome to replace it directly.

Lastmod: Tuesday, September 26, 2023

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