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I'm trying to get the v4l2loopback kernel module to work on a Debian Buster instance in Google Cloud.

I've tried the following three approaches (with the current kernel's headers installed):

  1. apt-get install v4l2loopback-dkms
  2. apt-get install v4l2loopback-source module-assistant && module-assistant auto-install v4l2loopback-source
  3. Clone the github repository and compile by hand.

In all cases, the kernel is successfully installed/compiled, but when I attempt to load the it I get a list of Unknown symbol messages from dmesg. Specifically, those are:

[ 1260.269419] v4l2loopback: Unknown symbol video_ioctl2 (err -2)
[ 1260.277130] v4l2loopback: Unknown symbol v4l2_get_timestamp (err -2)
[ 1260.284609] v4l2loopback: Unknown symbol v4l2_ctrl_handler_init_class (err -2)
[ 1260.293824] v4l2loopback: Unknown symbol video_devdata (err -2)
[ 1260.301289] v4l2loopback: Unknown symbol v4l2_ctrl_new_custom (err -2)
[ 1260.308415] v4l2loopback: Unknown symbol video_unregister_device (err -2)
[ 1260.372483] v4l2loopback: Unknown symbol video_device_alloc (err -2)
[ 1260.380400] v4l2loopback: Unknown symbol v4l2_device_register (err -2)
[ 1260.388960] v4l2loopback: Unknown symbol __video_register_device (err -2)
[ 1260.396973] v4l2loopback: Unknown symbol v4l2_ctrl_handler_free (err -2)
[ 1260.405559] v4l2loopback: Unknown symbol v4l2_device_unregister (err -2)
[ 1260.424848] v4l2loopback: Unknown symbol video_device_release (err -2)

I don't know enough about kernel modules to really understand what this means, nor how to fix it.

This seems to be a specific issue related to the machine (Linux 4.19.0-17-cloud-amd64), because I can install the v4l2loopback modeul without any problems on my local machine.

Any suggestions on how to proceed?

What should be changed to successfully load the kernel?

Can you suggest additional information that might be useful?

Osvaldo
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Ingo
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  • Does this answer your question? [modprobe: ERROR: could not insert 'v4l2loopback': Unknown symbol in module, or unknown parameter (see dmesg)](https://stackoverflow.com/questions/68994307/modprobe-error-could-not-insert-v4l2loopback-unknown-symbol-in-module-or-u) – razimbres Dec 03 '21 at 18:00
  • Are you using a custom image or official GCP public image? – rriovall Dec 03 '21 at 21:20
  • @rriovall, I'm using a custom image built on top of the "debian-10" public one. – Ingo Dec 06 '21 at 10:25
  • @razimbres, that reply is for Ubuntu20.04 in AWS and although it appears that that should work with only minor modifications on Debian Buster in GCP, it doesn't. The `linux-modules-extra` package is not available. – Ingo Dec 06 '21 at 10:27
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    @razimbres pointer solves it partly: Switching to an Ubuntu 20.04 base image on GCP allows me to load the module. Thank you! – Ingo Dec 06 '21 at 15:16

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