modprobe: ERROR: could not insert 'v4l2loopback': Unknown symbol in module, or unknown parameter (see dmesg)

[DazWilkin]

Describe the bug

Challenged to run the End-to-End example cloud (!) VMs (GCP, DigitalOcean). Specifically modprobe v4l2loopback:

sudo modprobe v4l2loopback exclusive_caps=1 video_nr=1,2
modprobe: ERROR: could not insert 'v4l2loopback': Unknown symbol in module, or unknown parameter (see dmesg)

I suspect the issue is that dependenct modules aren't included on cloud VM kernels but I prefer to use cloud VMs because they're disposable and I can keep my primary workstation untainted by random installs.

Output of kubectl get pods,akrii,akric -o wide

N/A

Kubernetes Version: [e.g. Native Kubernetes 1.19, MicroK8s 1.19, Minikube 1.19, K3s]

N/A

To Reproduce
Steps to reproduce the behavior:

1. Create cloud VM (GCP, DigitalOcean)
2. Set up mock video devices (link)
3. Attempt modprobe v4l2loopback

Expected behavior

No errors

dmesg:

v4l2loopback: loading out-of-tree module taints kernel.
v4l2loopback: module verification failed: signature and/or required key missing - tainting kernel
v4l2loopback: Unknown symbol video_ioctl2 (err -2)
v4l2loopback: Unknown symbol v4l2_ctrl_handler_init_class (err -2)
v4l2loopback: Unknown symbol video_devdata (err -2)
v4l2loopback: Unknown symbol v4l2_ctrl_new_custom (err -2)
v4l2loopback: Unknown symbol video_unregister_device (err -2)
v4l2loopback: Unknown symbol video_device_alloc (err -2)
v4l2loopback: Unknown symbol v4l2_device_register (err -2)
v4l2loopback: Unknown symbol __video_register_device (err -2)
v4l2loopback: Unknown symbol v4l2_ctrl_handler_free (err -2)
v4l2loopback: Unknown symbol v4l2_device_unregister (err -2)
v4l2loopback: Unknown symbol video_device_release (err -2)

NOTE the taint and module verification error are warnings only and may be ignored

Additional context

The solution I've found is:

sudo apt update && \
sudo apt -y install modules-extra-$(uname -r) && \
sudo apt -y install dkms

NOTE the installs may possibly be combined

Then:

curl http://deb.debian.org/debian/pool/main/v/v4l2loopback/v4l2loopback-dkms_0.12.5-1_all.deb ...
sudo dpkg -i v4l2loopback-dkms_0.12.5-1_all.deb
sudo modprobe v4l2loopback exclusive_caps=1 video_nr=1,2

Succeeds!

On GCP:

dkms status
v4l2loopback, 0.12.5, 5.4.0-1028-gcp, x86_64: installed

On DigitalOcean:

dkms status
v4l2loopback, 0.12.5, 5.4.0-51-generic, x86_64: installed

Hopefully this will help others that get stuck.

[kate-goldenring]

@DazWilkin, do you think we can close this since you added instructions for e2e on the cloud? Then, if we see more people hit this error, then we could add the additional install instructions to the normal e2e:

sudo apt update && \
sudo apt -y install modules-extra-$(uname -r) && \
sudo apt -y install dkms

[DazWilkin]

Yes, please do!

I prefer to let repo owners decide whether to close|ignore comments.

I hope that's OK?

Thanks for asking.

[vladimirvivien]

Small correction: it should be linux-modules-extra-$(uname -r) in the solutions above, as in:

sudo apt update && \
sudo apt -y install linux-modules-extra-$(uname -r) && \
sudo apt -y install dkms