Null characters (^@) appear in console at boot
 

Hi everyone,

I am running arch linux on an HP Spectre x360 laptop (model 13-4101dx), with an intel processor.

When I boot the computer and arrive at the login screen in the console, the computer starts typing null characters (^@) in the console by itself. This issue persists for about 1 minutes, and it makes it difficult to type the username/password. The same issue has been reported by several others on HP laptops (as well as desktops), and it seems to be due a bug causing a kernel module (peaq_wmi) to send a steady stream of null characters (caret notation) to the console every few seconds. It does not appear to be a hardware issue, as this is a frequently reported bug and others have tried disconnecting keyboards to desktops, and the issue persists.

https://bbs.archlinux.org/viewtopic.php?pid=1739030
https://bbs.archlinux.org/viewtopic.php?id=222316
https://bbs.archlinux.org/viewtopic.php?id=230330
https://www.reddit.com/r/archlinux/c...n_login_field/
https://bugzilla.redhat.com/show_bug.cgi?id=1497861

The solution given in several of those threads is to blacklist the culprit module (seems to be input_polldev in their case, which peaq_wmi depends on). However, the input_polldev module doesn't seem to be running on my computer, so I'm not sure which module is causing the issue here.

Separately, in one of the earlier threads, a user wrote:

https://bbs.archlinux.org/viewtopic.php?id=222316

However, I'm not sure which button this is referring to.

If I could figure out the key causing this issue, I might be able to use xmodmap to assign 'NoSymbol' to that button by running the following code, where XXX is the corresponding key number.

My confusion stems from the fact that in those previous threads, the users suggest blacklisting "input_polldev" as the solution (or, alternatively, to assign 'NoSymbol' to the key causing the null byte to be sent to the console), but I don't seem to be running the module and don't know which key the "lid virtual button" is referring to.

That's why I'm struggling a bit with how to proceed.

As a current work around, I am using a display manager (LXDM) to login, and these characters don't appear there. But ideally I'd drop the display manager.

Any input would be much appreciated, thank you.

what i read is that you haven't actually tried any of the solutions you found, you were just "wondering".
am i correct?
if i am, i suggest you do just that.
if i am not, show us something.

Hi Ondoho,
As I indicated in my 1st post, I've come across two apparent solutions/workarounds.

1) Disable the kernel module "input_polldev" or (2) disable the "lid virtual button" using xmodmap.

As I showed in my lsmod in the 1st post, "input_polldev" isn't running on my computer, so I can't disable it. I instead tried disabling a number of other potential culprits (all the hid_sensor_* modules and ax25), to no avail. And I don't know what the "lid virtual button" is referring to (which is why I posted my xmodmap -pk output above), so I'm not sure what to do there.

I ran libinput debug-events to try to see what was going on, and I think I identified the spurious input. The null bytes (series of three ^@ in a row) showed up after I switched to tty2 login prompt, closed the lid, and opened it. This is what was captured by libinput:

I'm probably missing something obvious, but the KEY_WLAN doesn't correspond to any key in xmodmap -pk, so I'm not sure how to disable this event from occurring.

does it have a wifi on/off switch (or something similar)?

Only an airplane mode button. When I click that button while libinput debug-events is running, it shows this though:

you posted an xmodmap -pk list. There is an XF86RFKill (line 255) and also a XF86WLAN (line 246).
I don't know if it was usable, but you can try to remap that event to something else. Probably.

Thanks for spotting the WLAN key, which might be related to KEY_WLAN. Would you recommend I try the following command:

I cannot recommend you anything, because I don't know if that helps. But if you don't have any idea it is just a bit better than nothing. At least if you can't find anything else to do. By the way from here it looks like a keyboard (hardware) related error, but again, I'm unsure.

The reason I don't think it's a keyboard error is that it's a bug reported by numerous users of the HP Spectre x360 laptop (see threads in original post). Everyone is reporting same null bytes being sent to login console, and it appears to be due to a faulty module that is null bombing the console.

In any case, this didn't solve the issue (the xmodmap -pk in the 1st post already indicates that this keycode already has NoSymbol assigned to it, I think):