modprobe: FATAL: Module v4l2loopback not found in directory

Question

I run a debian 10 with kernel 5.9.0.0 I installed v4l2loopback from the official repo, as in sudo apt install v4l2*, which installed

sudo apt install v4l2*
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Note, selecting 'v4l2loopback-source' for glob 'v4l2*'
Note, selecting 'v4l2ucp' for glob 'v4l2*'
Note, selecting 'v4l2loopback-dkms' for glob 'v4l2*'
Note, selecting 'v4l2loopback-modules' for glob 'v4l2*'
Note, selecting 'v4l2loopback-utils' for glob 'v4l2*'

I have linux-headers-5.9.0-0.bpo.2-amd64 installed, and

uname  -a
Linux debian 5.9.0-0.bpo.2-amd64 #1 SMP Debian 5.9.6-1~bpo10+1 (2020-11-19) x86_64 GNU/Linux

When I try to modprobe for v4l2 though, this is what happens:

sudo modprobe v4l2loopback
modprobe: FATAL: Module v4l2loopback not found in directory /lib/modules/5.9.0-0.bpo.2-amd64

Folder exist, I can't see this module in it though. I tried purging v4l2, reinstalling, rebooting, nothing.

Any help?

Thanks!

EDIT: when trying to install them I actually have some error, here is the full output

sudo apt install v4l2loopback-dkms v4l2loopback-utils
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
  v4l2loopback-dkms v4l2loopback-utils
0 upgraded, 2 newly installed, 0 to remove and 1 not upgraded.
Need to get 0 B/54.6 kB of archives.
After this operation, 153 kB of additional disk space will be used.
Selecting previously unselected package v4l2loopback-dkms.
(Reading database ... 378603 files and directories currently installed.)
Preparing to unpack .../v4l2loopback-dkms_0.12.1-1_all.deb ...
Unpacking v4l2loopback-dkms (0.12.1-1) ...
Selecting previously unselected package v4l2loopback-utils.
Preparing to unpack .../v4l2loopback-utils_0.12.1-1_all.deb ...
Unpacking v4l2loopback-utils (0.12.1-1) ...
Setting up v4l2loopback-dkms (0.12.1-1) ...
Loading new v4l2loopback-0.12.1 DKMS files...
Building for 5.9.0-0.bpo.2-amd64
Building initial module for 5.9.0-0.bpo.2-amd64
Error! Bad return status for module build on kernel: 5.9.0-0.bpo.2-amd64 (x86_64)
Consult /var/lib/dkms/v4l2loopback/0.12.1/build/make.log for more information.
dpkg: error processing package v4l2loopback-dkms (--configure):
 installed v4l2loopback-dkms package post-installation script subprocess returned error exit status 10
Setting up v4l2loopback-utils (0.12.1-1) ...
Processing triggers for man-db (2.8.5-2) ...
Errors were encountered while processing:
 v4l2loopback-dkms
E: Sub-process /usr/bin/dpkg returned an error code (1)

The output is not very eloquent as to what the problem may be, I tried with a sudo dpkg --configure v4l2loopback-dkms but got the same error

Solution

I'll answer my own question. Since my kernel is 5.9.0.0, which I installed from buster-backports, while v4l2 was installed from buster repo, it was off.

I solved it by just installing that too from buster-backports and it works fine

Comments

[umläute]

installing everything starting with v4l2 is probably suboptimal. just install the packages you want (which is v4l2loopback-dkms and maybe v4l2loopback-utils). installing the DKMS-package will build the module - but this might fail! closely watch the apt output to see what it does (and where it succeeds or fails)

[arteteco]

thanks @umläute, I actually have troubles starting from the installation, I edited my question to add the details

[arteteco]

thanks @umläute, don't waste time re-reading my question, I found the problem and posted the solution. I just had to install v4l2 from buster-backports, where I got my kernel from.