[Solved] evtest behave differently on two pc's

[peer]

pc1: Debian 12 Bookworm KDE X
pc2: Debian 12 Bookworm KDE Wayland

The output of the command evtest (owner root) is different on both pc's
pc1:

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evtest
No device specified, trying to scan all of /dev/input/event*
Not running as root, no devices may be available.
Available devices:
/dev/input/event0:      AT Translated Set 2 keyboard
/dev/input/event1:      Power Button
/dev/input/event10:     HUION 256C PEN STYLUS
/dev/input/event11:     RFID Reader RFID Reader
/dev/input/event12:     RFID Reader RFID Reader Keyboard
/dev/input/event14:     HDA ATI HDMI HDMI/DP,pcm=3
/dev/input/event15:     HDA ATI HDMI HDMI/DP,pcm=7
/dev/input/event16:     HDA ATI HDMI HDMI/DP,pcm=8
/dev/input/event17:     HDA ATI HDMI HDMI/DP,pcm=9
/dev/input/event18:     HDA ATI HDMI HDMI/DP,pcm=10
/dev/input/event19:     HDA ATI HDMI HDMI/DP,pcm=11
/dev/input/event2:      Power Button
/dev/input/event20:     HDA Digital PCBeep
/dev/input/event21:     HDA Intel PCH Front Mic
/dev/input/event22:     HDA Intel PCH Rear Mic
/dev/input/event23:     HDA Intel PCH Line
/dev/input/event24:     HDA Intel PCH Line Out
/dev/input/event25:     HDA Intel PCH Front Headphone
/dev/input/event26:     Huion Tablet
/dev/input/event27:     Huion Tablet
/dev/input/event29:     Huion keyboard
/dev/input/event3:      YICHIP Wireless Device
/dev/input/event30:     Huion mouse
/dev/input/event4:      YICHIP Wireless Device Mouse
/dev/input/event5:      YICHIP Wireless Device System Control
/dev/input/event6:      PC Speaker
/dev/input/event7:      YICHIP Wireless Device Consumer Control
/dev/input/event8:      HUION Huion Tablet_H640P Keyboard
/dev/input/event9:      Logitech USB Trackball
Select the device event number [0-30]: 

pc2:

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evtest
No device specified, trying to scan all of /dev/input/event*
Not running as root, no devices may be available.
Available devices:
Select the device event number [0-30]: 

On pc1 the devices are shown and I can execute the command without root
On pc2 the devices are not shown and I cannot execute the command without root

groupinf0:
pc1:

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groups
peer disk cdrom floppy sudo audio dip video plugdev input kvm netdev bluetooth lpadmin scanner libvirt libvirt-qemu

pc2:

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groups
peer cdrom floppy sudo audio dip video plugdev users netdev bluetooth lpadmin scanner

After this I added the group 'input' on pc2 and now the command evtest works also without on pc2.

My question:
When I look at the properties of the file evtest I see that the owner is 'root' and the group is 'root'. But members of the group 'input' also can execute the command without sudo. I discovered this by trial and error. How can I find which groups are able to execute the command (evtest) without sudo????

[fabien]

Hello,

When I look at the properties of the file evtest I see that the owner is 'root' and the group is 'root'.

I assume you mean the executable /usr/bin/evtest
The permissions of this file should be rwxr-xr-x (755) which means executable by anyone.

But members of the group 'input' also can execute the command without sudo. I discovered this by trial and error. How can I find which groups are able to execute the command (evtest) without sudo????

According to evtest's manual

The output of evtest shows the information presented by the kernel

namely in /dev/input/
and

evtest needs to be able to read from the device; in most cases this means it must be run as root.

However, files in /dev/input/ belong to root/input with permissions 660, e.g.

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$> ls -l /dev/input/event1
crw-rw---- 1 root input 13, 65 Apr 23 12:11 /dev/input/event1

and are therefore readable (and writable) by user root or group input. If your user is in the input group, evtest is “able to read from the device”.

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$> find /dev/ -group "input"

will show you all these files.

May also be relevant:

If evtest does not show any events even though the device is being used, the device may be grabbed by a process (EVIOCGRAB). This is usually the case when debugging a synaptics device from
within X. VT switching to a TTY or shutting down the X server terminates this grab and synaptics devices can be debugged.

The following command shows the processes with an open file descriptor on the device:

fuser -v /dev/input/eventX

[peer]

Yes, it has to do with the event files in /dev/input/
They have as owner: root and as group: input